Laser system having a multi-pass amplifier and methods of use

<u>Cross-Reference to Related Applications</u>

0001The present application claims priority to <patcit id="pcit0001" dnum="US62430862" dnum-type="L"><text>United States Provisional Patent Application Serial No. 62/430,862, entitled "Laser System Having Novel Multi-Stage Amplifier and Methods of Use," filed on December 6, 2016</text></patcit>.

<u>Background</u>

0002Laser systems are presently used in a wide variety of applications. In the past, conventional optically-pumped solid-state lasers utilized broadband arc lamps or flashlamps to laterally or transversely pump the solid-state laser medium in a resonant cavity. Over time diode-pumped solid state laser systems have become the preferred optically-pumped laser systems for most applications.

0003While presently available diode-pumped solid state laser systems have proven useful in the past, a number of shortcomings have been identified. For example, some high power applications require high power pumping of the laser gain media. Typically, a gain media receives a pump signal within a confined region of a facet formed on the gain media. As a result, undesirable effects such as thermal lensing within the gain media have proven to be problematic. In addition, injecting a seed signal into the gain media within the confines of a compact facet has led to a decrease the operational lifetime of some gain media.

0004In light of the foregoing, there is an ongoing need for a laser system having a multi-stage amplifier.

0005An example of a laser system is disclosed in <patcit id="pcit0002" dnum="US20111243166A1"><text>US 20111243166 Al</text></patcit>. The laser system comprises a laser amplifier including a laser active slab with a source of pump power to amplify an input laser beam, the laser active slab including a block of laser active material designed to minimize parasitic amplified spontaneous emission. The source of pump power may be one or more laser diode bars producing a gain sheet in the laser active slab. Lateral faces may of the slab include optical coatings highly transmitting at a wavelength of the pump power and highly reflecting at a lasing wavelength to provide a folded path for the input laser beam though the gain sheet. The laser amplifier includes external mirrors highly reflecting at the lasing wavelength positioned and oriented to provide one or more additional zig-zag passes through the gain sheet for the input laser beam and to provide a multi-pass-amplified laser.

<u>Summary</u>

0006Various embodiments of laser systems having a multi-stage amplifier are disclosed in herein. In some embodiments, a laser system that utilizes a single multi-pass amplifier for use in various laser systems will be described in detail in the following paragraphs. In other embodiments, a laser system that utilizes a first amplifier and/or pre-amp and at least one multi-pass amplifier for use in various laser systems will be described in detail in the following paragraphs. In one aspect, the present application is directed to a laser system disclosed in claim 1.

0007Preferred embodiments of the laser system are disclosed in the dependent claims.

0008The first mirror and second mirror may comprise a curved mirror configured to reflect the at least one amplifier output signal within the output wavelength range.

0009Other features and advantages of the laser system having a multi-pass amplifier and method of use as described herein will become more apparent from a consideration of the following detailed description.

<u>Brief Description of the Drawings</u>

0010The novel aspects of the laser system having a multi-stage amplifier as disclosed herein will be more apparent by consideration of the following figures, wherein: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Figure 1</figref> shows a schematic diagram of an embodiment of a laser system having a multi-stage amplifier architecture;</li><li><figref idref="f0001">Figure 2</figref> shows a schematic diagram of another embodiment of a laser system having a multi-stage amplifier architecture wherein multiple first amplifier stages are included therein;</li><li><figref idref="f0002">Figure 3</figref> shows a schematic diagram of another embodiment of a laser system having a multi-stage amplifier architecture wherein multiple second amplifier stages are included therein ;</li><li><figref idref="f0002">Figure 4</figref> shows a schematic diagram of another embodiment of a laser system having a multi-stage amplifier architecture wherein multiple first amplifier stages and multiple second amplifier stages are included therein;</li><li><figref idref="f0003">Figure 5</figref> shows a schematic diagram of another embodiment of a laser system having a multi-stage amplifier architecture wherein multiple seed multiple first amplifier stages and second amplifier stages;</li><li><figref idref="f0003">Figure 6</figref> shows a schematic diagram of an embodiment of a seed laser system used in an embodiment of a laser system having a multi-stage amplifier architecture;</li><li><figref idref="f0004">Figure 7</figref> shows a schematic diagram of an embodiment of a first amplifier stage used in an embodiment of a laser system having a multi-stage amplifier architecture;</li><li><figref idref="f0005">Figure 8</figref> shows a schematic diagram of an embodiment of a second amplifier stage used in an embodiment of a laser system having a multi-stage amplifier architecture;</li><li><figref idref="f0006">Figure 9</figref> shows a schematic diagram of an embodiment of a second amplifier stage used in an embodiment of a laser system having a multi-stage amplifier architecture wherein a first reflector and at least a second reflector are used to seed the gain media device;</li><li><figref idref="f0007">Figure 10</figref> shows a schematic diagram of an embodiment of a second amplifier stage used in an embodiment of a laser system having a multi-stage amplifier architecture the gain media device is being pumped by multiple pump sources;</li><li><figref idref="f0008">Figure 11</figref> shows a schematic diagram of an embodiment of a first reflector and at least a second reflector used in an embodiment of a laser system having a multi-stage amplifier wherein the first reflector and second reflector are angled relative to the gain media device;</li><li><figref idref="f0008">Figure 12</figref> shows a schematic diagram of an embodiment of a first reflector and at least a second reflector used in an embodiment of a laser system having a multi-stage amplifier wherein the first reflector and second reflector are curved;</li><li><figref idref="f0009">Figure 13</figref> shows an elevated perspective view of an embodiment of a reflector in an embodiment of a laser system having a multi-stage amplifier wherein the reflector includes areas of high reflectance and areas of high transmission;</li><li><figref idref="f0010">Figure 14</figref> shows a schematic diagram of an embodiment of a second amplifier stage used in an embodiment of a laser system having a multi-stage amplifier architecture incorporating an embodiment of the reflector device shown in <figref idref="f0009">Figure 13</figref>;</li><li><figref idref="f0011">Figure 15</figref> shows graphically the effect of the thermal lens on amplified seed signal as it passes through gain media device multiple times for three different values of the thermal lens used in an embodiment of a laser system having a multi-stage amplifier;</li><li><figref idref="f0012">Figure 16</figref> shows graphically the effects of a variation in the distance between reflectors used in an embodiment of a laser system having a multi-stage amplifier;</li><li><figref idref="f0013">Figure 17</figref> show graphically the effects of using reflectors curved in the vertical direction on the size the variation of amplified seed signal used in an embodiment of a laser system having a multi-stage amplifier;</li><li><figref idref="f0014">Figure 18</figref> shows an elevated perspective view of a reflector in a laser system having a multi-stage amplifier wherein the reflector includes a single area of high reflectance and a single of high transmission; and</li><li><figref idref="f0015">Figure 19</figref> shows a schematic diagram of an embodiment of a second amplifier stage used in a laser system having a multi-stage amplifier architecture incorporating the reflector device shown in <figref idref="f0014">Figure 18</figref>.</li></ul>

<u>Detail Description</u>

0011Various embodiments of multi-stage laser amplifiers for use in various laser systems will be described in detail in the following paragraphs. <figref idref="f0001 f0002 f0003">Figures 1-5</figref> show various embodiments of laser systems incorporating multi-stage amplifier configurations. As shown in <figref idref="f0001">Figure 1</figref>, in one embodiment the laser system 10 includes at least one seed source 20 configured to output at least one seed signal 56 to at least one first amplifier stage 60. <figref idref="f0001">Figure 1</figref> shows the seed source 20 outputting a single seed signal 56 to a single first amplifier stage 60. In contrast, <figref idref="f0001">Figures 2</figref> and <figref idref="f0002">3</figref> shows a single seed source 20 outputting multiple seed signals 56 to a multiple first amplifier stages 60a, 60b. In addition, <figref idref="f0002">Figure 3</figref> shows a single seed source 20 outputting a single seed signal to a single first amplifier stage 60 which outputs multiple amplified signals 86 to multiple 2^nd amplifier stages 100a and 100b. In addition, <figref idref="f0002">Figure 4</figref> shows a single seed source 20 outputting multiple seed signals for multiple 1^st amplifiers stages a 60a and 60b and multiple 2^nd stages 100a and 100b. In addition, as shown in <figref idref="f0003">Figure 5</figref>, multiple seed sources 20a, 20b may be used to deliver multiple seed signals 56 to one or more first amplifier stages 60a, 60b. Those skilled in the art will appreciate that any number of seed sources may be configured to output any number of seed signals to any number of first amplifier stages 60.

0012As shown in <figref idref="f0001">Figure 1</figref>, optionally one or more optical systems, devices, or components 58 (hereinafter "optical device") may be positioned anywhere within the various embodiments of the laser systems 10 shown in <figref idref="f0001 f0002 f0003">Figures 1-5</figref>. More specifically, <figref idref="f0001">Figures 1</figref> and <figref idref="f0002">4</figref> show various embodiments of a laser system having one or more optical systems 58 positioned therein, however, it is understood that any number of optical systems and/or device 58 may be used throughout the various embodiments of laser systems shown in <figref idref="f0001 f0002 f0003">Figures 1-5</figref>. In one embodiment, the optical device 58 comprises one or more wavelength filters. Exemplary wavelength filters include, without limitation, one or more dichroic mirrors, wavelength selective devices, optical filters, and the like. In another embodiment, the optical device 58 comprises one or more lenses. In another embodiment, the optical device 58 comprises one or more sensors. Those skilled in the art will appreciate that any variety of optical devices may be used in the present laser system, including, without limitations, lenses, filters, mirrors, sensors, modulators, polarizers, waveplates, masks, attenuators, wavelength filters, spatial filters, and the like.

0013Referring again to <figref idref="f0001">Figure 1</figref>, the first amplifier stage 60 may be configured to receive the seed signal 56 from the seed source 20 and amplify the seed signal 56 to produce at least one amplified seed signal 86. In one embodiment, the first amplifier stage 60 is configured to output a single amplified seed signal 86 to a single second amplifier stage 100 (See <figref idref="f0001">Figures 1</figref> and <figref idref="f0003">5</figref>). In contrast, <figref idref="f0001">Figure 2</figref> shown multiple first amplifier stages 60a, 60b each outputting a single amplified seed signal 86 to a single second amplifier stage 100. In the alternative, <figref idref="f0002">Figure 3</figref> shows an embodiment of a laser system 10 having a single first amplifier stage 60 outputting multiple amplified seed signals 86 to multiple second amplifier stages 100a, 100b. Any number of first amplifier stages 60 may be used within the laser system 10. Further, in the embodiment shown in <figref idref="f0001">Figures 2</figref>, the multiple first amplifier stages 60a, 60b are shown in a parallel configuration. However, those skilled in the art will appreciate that the first amplifier stages 60a, 60b may be sequentially positioned (in series). Similarly, the various components of the laser system 10, including the seed source 20a, 20b, first amplifier stage 60a, 60b, and/or second amplifier stage 100a, 100b, if present, may be configured in either a parallel architecture or sequentially in a serial configuration or any combination thereof.

0014As shown in <figref idref="f0001">Figure 1</figref>, the laser system 10 may include at least one second amplifier stage 100 therein. In the illustrated embodiment, the second amplifier stage 100 may be in communication with one or more first amplifier stages 60 positioned within the laser system 10. <figref idref="f0001">Figures 1 and 2</figref> show an embodiment of a laser system having a single second amplifier stage 100 positioned therein. Optionally, as shown in <figref idref="f0002 f0003">Figures 3-5</figref>, various embodiments of laser systems having multiple second amplifier stages 100a, 100b positioned therein. In one embodiment, the second amplifier stages 100a, 100b are in communication with a single first amplifier stage 60. Optionally, multiple second amplifier stages 100a, 100b are in communication with one or more first amplifier stages 60a, 60b (See <figref idref="f0001">Figures 2</figref>, <figref idref="f0002">4</figref> and <figref idref="f0003">5</figref>). Any number of second amplifier stages 100 may be used in the laser system 10. Further, any number of additional amplifier stages may be used with the laser system 10.

0015As shown in <figref idref="f0001 f0002 f0003">Figures 1-5</figref>, at least one amplified output signal 110 may be emitted from the one or more second amplifier stages 100 positioned within the laser system 10. As shown in <figref idref="f0001">Figures 1 and 2</figref>, a single amplified output signal 110 is emitted from the second amplifier stage 100. In the alternative, <figref idref="f0002 f0003">Figures 3-5</figref> show various embodiments of a laser system 10 wherein multiple amplified output signals 110 are emitted from numerous second amplifier stages 100 positioned within the laser system 10. In the illustrated embodiments, the amplified output signal 110 is directed into one or more optical systems or devices 200 configured to output at least one output signal 250. In one embodiment, optical system 200 comprises one or more isolators. In another embodiment, the optical system 200 comprises one or more modulators. Optionally, the optical system 200 may comprise at least one telescope. Further, the optical system 200 may comprise one or more laser systems, amplifiers, and the like. For example, the optical system 200 may comprise one or more additional multi-stage amplifiers. The additional multi-stage amplifier 200 may include one or more single pass amplifiers. Optionally, the additional multi-stage amplifier 200 may include a one or more multi-pass amplifiers. In another embodiment, the optical system 200 may include at least one single stage amplifier. Optionally, the optical system 200 may include one or more nonlinear optical crystals. Optionally, the laser system 10 need not include an optical system 200.

0016<figref idref="f0003">Figure 6</figref> shows a schematic view of an embodiment of a seed source 20 for use with the laser system 10 shown in <figref idref="f0001">Figure 1</figref>. As shown, the seed source 20 includes at least one seed laser 22 therein. In one embodiment, the seed laser 22 comprises a diode laser system. For example, the seed laser 22 may comprise one or more gain switched diode laser system. In another embodiment, the seed laser comprises one or more fiber amplified diode laser sources. Further, the seed source 20 may comprise an injection seed diode laser system. Optionally, the seed source 22 may comprise one or more fiber lasers devices. In short, any type of laser system may be used as the seed laser 22 in the seed source 20.

0017The seed laser 22 may be configured to output at least one seed signal 24 having a wavelength from about 400 nm to about 1400 nm. For example, in one embodiment, the seed laser 22 outputs a seed signal 24 having a wavelength from about 600 nm to about 1200 nm. For example, the seed signal 24 may have a wavelength of about 1064 nm. In yet another embodiment, the seed signal 24 has a wavelength of about 1030 nm. Further, the seed laser 22 may be configured to output a pulsed output. For example, the seed laser 22 may be configured to output a seed signal 24 having a repetition rate of 100 kHz or more. In another embodiment, the seed laser 22 may be configured to output a seed signal 24 having a repetition rate of 1MHz or more. Optionally, the seed laser 22 may be configured to output a seed signal 24 having a repetition rate of 15MHz or more. For example, the seed laser 22 may be configured to output a seed signal 24 having a repetition rate of about 20 MHz. Optionally, the seed laser 22 may be configured to output a seed signal 24 having a repetition rate of 10 kHz.

0018Referring again to <figref idref="f0003">Figure 6</figref>, the seed laser 22 may be configured to output a seed signal 24 having any desired pulse width. In one embodiment, the seed laser 22 may be configured to output a seed signal 24 having a pulse width of less than about 100 ps. In another embodiment, the seed laser 22 may be configured to output a seed signal 24 having a pulse width of less than about 50 ps. Optionally, seed laser 22 may be configured to output a seed signal 24 having a pulse width of less than about 25 ps. In another embodiment, the seed laser 22 may be configured to output a seed signal 24 having a pulse width of less than about 1 ps. Further, the seed laser 22 may be configured to output a seed signal 24 having a power of about 1µW to about 200 µ W. For example, the seed laser 22 may be configured to output a seed signal 24 having a power of about 40 µ W to about 80 µ W. In another embodiment, the seed laser 22 may be configured to output a seed signal 24 having a power of about 65µ W to about 85 µ W.

0019Referring again to <figref idref="f0003">Figure 6</figref>, the seed source 20 may include one or more optical filters 26 configured to filter the seed signal 24 to produce at least one filtered or chirped signal 32 (hereinafter "filter signal"). In one embodiment, the optical filter 26 comprises at least one Bragg reflector. For example, the optical filter 26 may comprise at least one chirped fiber Bragg grating. In the illustrated embodiment, the optical filter 26 is in communication with at least one sensor or control device 28 via at least one conduit 30. For example, during use the control device 28 may be configured to permit the user to selectively vary the range of wavelength transmission through the optical filter 26. As such, the wavelength characteristics of the chirped signal 32 may be easily varied. Optionally, the optical filter 26 may be configured to permit the user to selectively adjust any variety characteristics of the chirped signal 32.

0020As shown in <figref idref="f0003">Figure 6</figref>, a first amplifier 34 may be included within the seed source 20 to amplify the chirped signal 32. In one embodiment, the first amplifier 34 comprises at least one fiber amplifier. In one embodiment, the type of first amplifier 34 and second amplifier 42 (if present) used in the seed source 20 may dependent on the type of amplifier stage 60 and second amplifier stage 100 used in the laser system 10. For example, a Yb:fiber amplifier operating at a wavelength of about 1030 nm may be used as the first amplifier 34 in the seed source 20 if the first and second amplifier stages 60, 100 include Yb:YAG. In contrast, a Yb:fiber amplifier operating at a wavelength of about 1064 nm may be used as the first amplifier 34 in the seed source 20 if the first and second amplifier stages 60, 100 include Nd:YVO₄. Optionally, any variety of devices may be used in the seed source 20. The first amplifier 34 is configured to amplify the signal 32 to produce at least one amplified seed signal 36, which may be directed into at least one modulator system or device 38.

0021Referring again to <figref idref="f0003">Figure 6</figref>, the modulator device 38 is configured to alter the repetition frequency of the pulsed amplified seed signal 36 to produce at least one modulated amplified seed signal 40. In one embodiment, the modulator device 38 is configured to output a modulated seed signal 40 having a repetition rate of about 5 kHz to about 1000 kHz. In another embodiment, the modulator device 38 is configured to output a modulated amplified seed signal 40 having a repetition rate of about 100 kHz to about 500 kHz. Optionally, the modulator device 38 is configured to output a modulated amplified seed signal 40 having a repetition rate of about 250 kHz to about 350 kHz. For example, the modulator device 38 is configured to output a modulated amplified seed signal 40 having a repetition rate of about 333 kHz. In one embodiment, the modulator device 38 is configured to output a modulated seed signal 40 having a repetition rate greater than 1000 kHz. In one embodiment, the modulator device 48 comprises an acousto-optic modulator. Optionally, any variety of alternate devices may be used, including, without limitations, electro-optic modulators, amplitude modulators, phase modulators, liquid crystal modulators and the like. In an alternative embodiment seed source 20 does not include modulator device 38.

0022As shown in <figref idref="f0003">Figure 6</figref>, at least one second amplifier 42 may be included within the seed source 20 to amplify the modulated amplified seed signal 40 to produce at least one amplified modulated signal 44. In one embodiment, the second amplifier 42 comprises at least one Yb:fiber amplifier. Optionally, any variety of devices may be used in the seed source 20. For example, solid-state amplifiers may optionally be used in place of or in addition to fiber amplifiers. Further, any number of additional amplifiers may be used in the seed source 20. The amplified modulated signal 44 may be directed into at least one isolator 46 positioned within or in communication with the seed source 20. In one embodiment, the isolator 46 is configured to reduce or eliminate back reflections of the amplified modulated signal output 56 in the seed source 20. Those skilled in the art will appreciate that any number of isolators 46 may be used anywhere within the seed source 20. The isolator 46 may be configured to output at least one seed signal 56 to at least one first amplifier stage 60 of the laser system 10. In one embodiment, the seed signal 56 has a pulse width of about 1ps to about 100 ps and a pulse energy of about 10 µJ to about 70 µJ. For example, the seed signal 56 may have a pulse width of about 20 ps and a pulse energy of about 40 µJ. Further, the seed signal 56 may have a repetition rate of about 300 kHZ to about 450 kHz and a power of about 5mW to about 100 mW. Optionally, any variety of additional optical elements or devices may be used in the seed source 20, including, without limitations, lenses, mirrors, fold mirrors, planar mirror, curved mirror, dichroic filters, notch filters, gratings, sensors, optical filters, attenuators, modulators, circulators, fiber Brag gratings, laser diodes, volume Bragg gratings, and the like. In the illustrated embodiment, the various components of the seed source 20 are positioned within at least one housing 50. Those skilled in the art will appreciate that the various components of the seed source 20 may be positioned within multiple housings or may, in the alternative, be located within another subsystem of the laser system 10.

0023<figref idref="f0004">Figure 7</figref> shows an embodiment of the first amplifier stage 60 shown in <figref idref="f0001 f0002 f0003">Figures 1-5</figref> above. As shown, the first amplifier stage 60 may include at least one housing 62 configured to contain the various components of the first amplifier stage 60 therein. Optionally, the first amplifier stage 60 need not include a housing 62. At least one first amplifier pump source 64 may be used to generate at least one pump signal 76. In the illustrated embodiment, the first amplifier pump source 64 comprises a fiber coupled diode pump source configured to output at least one pump signal 76 having a wavelength from about 600 nm to about 1000 nm; although those skilled in the art will appreciate that any variety of pump source may be used within the first amplifier pump source 64. In one embodiment, the pump signal 76 has a wavelength of about 900 nm to about 1000 nm. For example, the pump signal 76 may have a wavelength of about 940 nm. In another embodiment, the pump signal 76 may have a wavelength of about 969 nm. Optionally, the pump signal 76 may have a wavelength of about 808 nm. In another embodiment, the pump signal 76 may have a wavelength of about 880 nm. Further, the pump source 62 may be configured to output a continuous wave pump signal or, in the alternative, a pulsed pump signal. For example, the pump signal 76 may have a repetition rate of about 1 kHz to 100MHz or more. For example, in one embodiment the pump signal 76 has a repetition rate of about 10 kHz. In another embodiment, the pulse signal 76 has a repetition rate of about 50 MHz to about 125 MHz.

0024Referring again to <figref idref="f0004">Figure 7</figref>, at least one fiber optic conduit 66 may be used to deliver the pump signal 76 to a desired location. Optionally, the pump source 64 need not include a fiber optic conduit 66. The fiber optic conduit 66 terminates with at least one pump signal delivery system 70. In one embodiment, the pump signal delivery system 70 comprises a cleaved fiber optic face. In another embodiment, the pump signal delivery system 70 may include one or more lenses, mirrors, filters, sensors, positioning devices (such a v-grooves, chucks, and the like), and similar devices. In the illustrated embodiment, at least one optical component 72 is coupled to the pump signal delivery system 70, although the pump signal delivery system 70 may include such an element therein or may operate without including such a device.

0025As shown, the pump signal 76 is directed out of the pump signal delivery system 70, traverse through at least one reflector 74, and is incident upon at least one gain media 82 positioned within the first amplifier stage 60. In one embodiment, the reflector 74 comprises at least one dichroic mirror configured to transmit at least one optical signal having a wavelength of less than about 1000 nm there through, while reflecting substantially all light having a wavelength of greater than about 1000 nm. Those skilled in the art will appreciate that any variety of optical reflectors configured to transmit at least one optical signal having a wavelength of less than about 1000 nm there through, while reflecting substantially all light having a wavelength of greater than about 1000 nm may be used in the present system. Further, the reflector 74 may be configured to transmit at least one optical signal having a wavelength of less than about 1000 nm there through, while reflecting substantially all light having a wavelength of greater than about 1020 nm. In another embodiment, Further, the reflector 74 may be configured to transmit at least one optical signal having a wavelength of less than about 1000 nm there through, while reflecting substantially all light having a wavelength of greater than about 1020 nm. In another embodiment, the reflector 74 may be configured to transmit multiple optical signals. For example, the reflector 74 may be configured to transmit at least one optical signal having a wavelength of less than about 1000 nm and at least one optical signal having a wavelength of greater than about 1100 nm, while substantially reflecting all light having a wavelength of about 1064 nm. In another embodiment, the reflector 74 may be configured to transmit at least one optical signal having a wavelength of less than about 1000 nm and at least one optical signal having a wavelength of greater than about 1100 nm, while substantially reflecting all light having a wavelength of about 1030 nm.

0026Referring again to <figref idref="f0004">Figure 7</figref>, optionally at least optical element 80 may be positioned anywhere within the first amplifier stage 60. Exemplary optical elements 80 include, without limitations, fold mirrors, planar mirror, curved mirrors, lenses, thermal management devices, fans, chillers, filters, and the like. As shown, the pump signal 76 traverses through the optical element 80 and is incident on the gain media 82. In one embodiment, the gain media 82 comprises at least one slab, rod, disk, or similar body constructed of a desired gain material. Exemplary gain materials include, without limitations, Nd:YVO₄, Nd:GdVO₄, Nd:YAG, Nd:YLF, Nd:glass, Yb:YAG, Yb:KGW, Yb:CaF₂, Yb:CALGO, Yb:Lu₂O₃, Yb:S-FAP, Yb:glass, semiconductor gain media, ceramic laser materials, and the like.

0027As shown in <figref idref="f0004">Figure 7</figref>, at least one seed signal 56 from at least one seed source (See <figref idref="f0001 f0002 f0003">Figures 1-5</figref>) is incident on the gain media 82 which amplifies the seed signal 56 to output at least one amplified seed signal 86. For example, in one embodiment, a seed signal 56 has a pulse width of about 20 ps, a pulse energy of about 40 µJ, a repetition rate of about 333 kHz, and a power of about 5mW to about 15 mW prior to amplification. Thereafter, the first amplifier stage 60 may be configured to output at least one amplified seed signal 86 may having a pulse width of about 20 ps, a pulse energy of about 18 µJ, a repetition rate of about 333 kHz, and a power of about 5W to about 15 W to the second amplifier stage 100.Those skilled in the art will appreciate that any number of first amplifier stages 60 may be used in the laser system 10.

0028<figref idref="f0005 f0006 f0007 f0008 f0009 f0010">Figures 8-14</figref> show various embodiments of a second amplifier stage 100 for use in a multi-stage amplifier for laser systems. As shown, the second amplifier stage 100 may be positioned within housing 112 or, in the alternative, may be positioned within the housing of a larger optical system or laser. As shown, the second amplifier stage 100 includes at least one gain media device 120 therein. In one embodiment, the gain media device 120 is Yb:YAG. In another embodiment, the gain media device 120 is Nd:YVO₄. Exemplary gain materials include, without limitations, Nd:YVO₄, Nd:GdVO₄, Nd:YAG, Nd:YLF, Nd:glass, Yb:YAG, Yb:KGW, Yb:CaF₂, Yb:CALGO, Yb:Lu₂O₃, Yb:S-FAP, Yb:glass, semiconductor gain media, ceramic laser materials, and the like. In one embodiment, the gain media device 120 comprises at least one slab, rod, disk, or similar body constructed of a desired gain material. For example, in the illustrated embodiments, the gain media device 120 comprises elongated facets F_Lon and compact facets F_Com. As such, the length of the elongated facets F_Lon may be greater than the length of the compact facets F_Com. In the illustrated embodiments, the energy and/or fluence of the seed signal 86 incident on the gain media device 120 is more distributed over at least one elongated facet F_Lon (i.e. transverse pumping) thereby reducing the effects of thermal lensing while reducing the likelihood of damaging the gain media device 120. In the alternative, those skilled in the art will appreciate that the gain media device 120 may be seeded via compact facets F_Com. In another embodiment, the gain media device 120 may be seeded via the elongated facets F_Lon and compact facets F_Com. As a result, those skilled in the art will appreciate that the gain media device 120 may be manufactured in any variety of shapes, dimensions, and configurations.

0029Referring again to <figref idref="f0005 f0006 f0007 f0008 f0009 f0010">Figures 8-14</figref>, the gain media device 120 may be proximate to at least one reflector. In the illustrated embodiment, the gain media device 120 is positioned between two reflectors 132 configured to reflect at least a portion of at least one amplified signal 86 from at least one first amplifier stage 60 into the gain media device 120. The gain media device 120 is configured to be pumped by at least one pump source 122. Optionally, any variety of alternate laser systems may be used to pump the gain media device 120. Further, at least one pump source 122 may be configured to output at least one pump signal 130 having a wavelength from about 600 nm to about 1000 nm. In one embodiment, the pump signal 130 has a wavelength of about 900 nm to about 1000 nm. For example, the pump signal 130 may have a wavelength of about 940 nm. In another embodiment, the pump signal 130 may have a wavelength of about 969 nm. Optionally, the pump signal 130 may have a wavelength of about 808 nm. In another embodiment, the pump signal 130 may have a wavelength of about 880 nm. Further, the pump source 122 may be configured to output a continuous wave pump signal or, in the alternative, a pulsed pump signal. For example, the pump signal 130 may have a repetition rate of about 1 kHz to 100MHz or more. For example, in one embodiment the pump signal 130 has a repetition rate of about 10 kHz. In another embodiment, the pulse signal 130 has a repetition rate of about 50 MHz to about 125 MHz.

0030In the illustrated embodiment, multiple fiber coupled diode pump sources 122 are configured to provide one or more pump signals 130 to the gain media device 120. In the illustrated embodiment, the diode pump source 122 is coupled to at least one fiber optic conduit 126. The fiber optic conduits 126 may be, but need not be, coupled to one or more pump signal delivery systems 124 (See <figref idref="f0007">Figure 10</figref>). In one embodiment, the pump signal delivery system 124 may comprise one or more than one v-grooves or similar positioning features configured to align or otherwise position one or more fiber optic conduits 126 in close proximity. In one embodiment the fiber optic conduits 126 are separated by a distance less than about 500 um. In another embodiment the fiber optic conduits 126 are separated by a distance greater than about 500 um. In yet another embodiment the fiber optic conduits 126 are separated by a distance of about 100 um. As such, the fiber optic conduits 126 may be positioned so as to produce the output having an elongated profile such as the output of an elongated pump source such as a diode bar, lightpipe, waveguide, or similar structure. As shown in <figref idref="f0007">Figure 10</figref>, the pump signal delivery system 124 may include one or more filters, sensors, lenses and the like, configured to direct the pump signal 130 to the gain media device 120. For example, in the illustrated example, one more lenses or similar optical components 128, 134 may be used to form a telescope, collimator, homogenizer, diffractive beam shaper, refractive beam shaper, lens array, and the like to condition the pump signal 130 for pumping the gain media device 120. In one embodiment, multiple optical components 128, 134 may be positioned proximate to multiple fiber optic conduits 126 (See Figure 100). In an alternate embodiment, a single optical component 128, 134 may be used rather the multiple individual optical components.

0031As shown <figref idref="f0005">Figures 8</figref> and <figref idref="f0007">10</figref>, the pump signal 130 is directed out of the pump signal delivery system 126, traverse through at least one reflector 132, and is incident upon at least one gain media device 120 positioned within the second amplifier stage 100. In the illustrated embodiment, the gain media device 120 is side-pumped by the pump signal 130. In another embodiment, the gain media device 120 is being pumped along an elongated facet of the gain media device 120 by the pump signal 130. Optionally, the gain media device 120 maybe end-pumped by the pump signal 130. In one embodiment, the reflector 132 comprises at least one dichroic mirror (planar or curved) configured to transmit at least one optical signal having a wavelength of less than about 1000 nm there through, while reflecting substantially all light having a wavelength of greater than about 1000 nm. Those skilled in the art will appreciate that any variety of optical reflectors configured to transmit at least one optical signal having a wavelength of less than about 1000 nm there through, while reflecting substantially all light having a wavelength of greater than about 1000 nm may be used in the present system. Further, the reflector 132 may be configured to transmit at least one optical signal having a wavelength of less than about 1000 nm there through, while reflecting substantially all light having a wavelength of greater than about 1020 nm. In another embodiment, Further, the reflector 132 may be configured to transmit at least one optical signal having a wavelength of less than about 1000 nm there through, while reflecting substantially all light having a wavelength of greater than about 1030 nm. In another embodiment, the reflector 132 may be configured to transmit multiple optical signals. For example, the reflector 132 may be configured to transmit at least one optical signal having a wavelength of less than about 1000 nm and at least one optical signal having a wavelength of greater than about 1100 nm, while substantially reflecting all light having a wavelength of about 1064 nm. In another embodiment, the reflector 132 may be configured to transmit at least one optical signal having a wavelength of less than about 1000 nm and at least one optical signal having a wavelength of greater than about 1100 nm, while substantially reflecting all light having a wavelength of about 1030 nm

0032As shown in <figref idref="f0005 f0006 f0007">Figures 8-10</figref>, the reflectors 132 receive the amplified seed signal 86 and repeatedly direct the seed signal 86 into the gain media device 120 for multi-pass amplification, thereby outputting an amplified output signal 110. For example, in one embodiment, the amplified seed signal has a pulse width of about 20 ps, a pulse energy of about 18 µJ, a repetition rate of about 333 kHz, and a power of about 5W to about 15 W, while output of the second amplifier stage 120 has a pulse width of about 20 ps, a pulse energy of about 175 µJ, a repetition rate of about 333 kHz, and a power of about 58 W or more.

0033<figref idref="f0008">Figure 11</figref> shows an alternate embodiment of reflectors used in the second amplifier stage 100. As shown, the reflectors 132 include a substantially planar body wherein at least one reflector is positioned at a slight wedge angle relative to the gain media device 120. In the alternative, <figref idref="f0008">Figure 12</figref> shows reflectors 132 include a substantially curved body. Those skilled in the art will appreciate that the reflectors 132 may be manufactured with having any desired shape, size, and configuration. At least one reflector includes areas or regions of high reflectance and areas or regions of high transmission at a desired wavelength formed thereon. For example, <figref idref="f0009">Figures 13</figref> and <figref idref="f0010">14</figref> shows an embodiment of a novel "striped" reflector 140 having a reflector body 142. As shown, the reflector body 142 includes areas or regions of high reflectance 144 at a desired wavelength and areas or regions of high transmission 146 at a desired wavelength. During use, the amplified seed signal 86 is incident on the reflector body 142. In one embodiment, at least one reflector body 142 is aligned such the amplified seed signal 86 is incident on the areas or regions of high reflectance 144 formed on the reflector body 142. As shown in <figref idref="f0010">Figure 14</figref>, parasitic signals 148 (including Raman-generated signals) formed within the gain media device 120 may be incident on the areas or regions of high transmission, thereby permitting the parasitic signals 148 to be extracted, suppressed, and/or not reflected by the reflectors 140. The areas of high reflectivity are configured to reflect substantially all the amplified output signal 110 through the gain media device 120, while the areas of high transmission are configured to transmit substantially all parasitic signals generated within the gain media device 120 as well as unabsorbed amplified seed signal 86 and unused pump signal 130 (See <figref idref="f0007">Figure 10</figref>) during use. As shown, parasitic signal or unused signal 148 may be transmitted through the reflectors 132. In another embodiment, the reflector 140 includes at least one area of high transmission 146 formed by applying at least one anti-reflective coating over the reflector body 142. Thereafter, one or more areas of high reflectance 144 at a desired wavelength may be formed by selectively applying a wavelength-dependent reflector material over the coated reflector body 142.

0034Referring now to <figref idref="f0005">Figure 8</figref>, the gain media device 120 receives one or more than one pump signals 130 from diode pump sources 122. In one embodiment the diode pump sources 122 cause a thermal lens to form in gain media device 120 that is substantially in the vertical direction. When amplified seed signal 86 passes through gain media device120 multiple times as illustrated in <figref idref="f0005">Figures 8</figref> and <figref idref="f0006">9</figref>, the amplified seed signal 86 may be affected by the thermal lens. <figref idref="f0011">Figure 15</figref> shows the effect of the thermal lens on amplified seed signal 86 as it passes through gain media device 120 multiple times for three different values of the thermal lens. It is evident that there is substantially one value of the thermal lens (f_TL = 600 mm) that results in the size of amplified seed signal 86 remaining substantially unchanged as it passes through the gain media device 120 and exits as amplified output 110. For any other value of the thermal lens the amplified seed signal 86 will change size as it is affected by the thermal lens in gain media device 120. This size change can lead to deleterious effects such as, but not limited to, loss of efficiency from poor overlap with the one or more than one pump beams, beam quality degradation, or even damage if the beam starts to interfere with other components or becomes small enough such as for the case shown in <figref idref="f0011">Figure 15</figref> where the thermal lens is f_TL = 400 mm.

0035<figref idref="f0012">Figure 16</figref> shows the variation of amplified seed signal 86 size for a substantially fixed thermal lens value f_TL = 400 mm for different distances of reflectors 132 from the gain media device 120. If in an alternative embodiment, as shown in <figref idref="f0012">Figure 16</figref>, the distance between reflectors 132 and the gain media device 120 was increased from about 15 mm to about 23 mm, amplified seed signal 86 size would again be substantially constant as it passes through gain media device 120 multiple times.

0036<figref idref="f0013">Figure 17</figref> shown the variation of amplified seed signal 86 size for yet another embodiment where the reflectors 132 are curved in the vertical direction. For a thermal lens value of f_TL = 400 mm and a separation of about 15 mm, amplified seed signal 86 size can again be substantially constant through multiple passes through gain media device 120 if the reflectors 132 have a curved surface with a radius of curvature of about -2400 mm.

0037As shown in <figref idref="f0014">Figure 18</figref>, the mirror or reflector 240 includes a reflector body 242. As shown, the reflector body 242 includes a large, single area or region of high reflectance 244 at a desired wavelength and a single area or region of high transmission 246 at a desired wavelength. For example, the area or region of high transmission 246 may be configured to transmit substantially all optical signals incident thereon. Further, the area or region of high reflectance 244 may be configured to selectively reflect substantially all light having a wavelength of greater than about 1000 nm while selectively transmitting light having a wavelength of less than about 1000 nm there through. In another embodiment, the area or region of high reflectance 244 may be configured to selectively reflect substantially all light having a wavelength of greater than about 1020 nm while transmitting all light having a wavelength of greater than about 1000 nm there through. Optionally, the area or region of high reflectance 244 may be configured to selectively reflect substantially all light having a wavelength of greater than about 1030 nm while transmitting all light having a wavelength of less than about 1000 nm there through. The reflector 132 may be configured to transmit multiple optical signals. For example, the reflector 132 may be configured to transmit at least one optical signal having a wavelength of less than about 1000 nm and at least one optical signal having a wavelength of greater than about 1100 nm, while substantially reflecting all light having a wavelength of about 1064 nm. In another embodiment, the reflector 132 may be configured to transmit at least one optical signal having a wavelength of less than about 1000 nm and at least one optical signal having a wavelength of greater than about 1100 nm, while substantially reflecting all light having a wavelength of about 1030 nm. In another embodiment, the area of high reflectance 244 and the area of high transmission 246 on the novel reflector body 242 may be substantially the same area. More specifically, the reflector 240 may comprise a dichroic mirror configured to reflect light within a desired wavelength range (i.e. about 1020 nm to about 1100 nm) while transmitting light outside the wavelength range there through. In another embodiment, the reflector 240 may comprise a notch mirror.

0038During use, as shown in <figref idref="f0015">Figure 19</figref>, the amplified seed signal 86 is incident on the reflector body 242. As shown, the amplified seed signal 86 may be incident along the elongated facet F_Lon of the gain media device 120. Similarly, the gain media device 120 may be pumped along the elongated facet F_Lon by at least one pump signal 230 as described in <figref idref="f0007">Figure 10</figref>. Further, the angle at which the amplified seed signal 86 is incident on the gain media device 120 may be selected to optimize the number of passes of the amplified seed signal 86 through the gain media device 120. The alignment of at least one reflector body 142 may also be configured to optimize the number of passes of the amplified seed signal 86 through the gain media device 12. As a result, the gain media device 120 may be permeated with the amplified seed signal 86, thereby suppressing the generation of parasitic signals (including Raman-generated signals) within the gain media device 120. The areas of high reflectivity 244 are configured to reflect substantially all the amplified output signal 110 generated through multiple passes through the gain media device 120. Further, the areas of high reflectance 244 are configured to transmit unabsorbed seed signal, unused pump signal 230, and/or parasitic signals generated during the amplification process there through. In the illustrated embodiment, the amplified output signal 110 may be extracted from multi-pass amplified 100 via at least one area or region of high transmission 246 formed on at least one reflector 240.

0039The embodiments disclosed herein are illustrative of the principles of the invention. Other modifications may be employed as long as they fall within the scope of the appended claims.