Wavelength-stabilized narrow-linewidth mode-locked picosecond laser system

Abstract

A wavelength-stabilized narrow-linewidth mode-locked picosecond laser system includes a laser cavity comprising an amplifier, a mode-locking element, and a fiber Bragg grating acting as a narrow-band reflector. The system includes a mount in which the fiber Bragg grating is mounted under tension, a tension control system for adjusting the tension, and a measurement device for providing a measurement output related to the current operating wavelength of the fiber Bragg grating. A microcontroller or other controller wavelength-stabilizes the laser by controlling the tension control system in response to the measured wavelength.

Description

[Technical field]

[0001] The present invention relates to a wavelength stabilized narrow linewidth modelocked picosecond laser system. [Background technology]

[0002] Mode-locking is often used to generate extremely short pulses (e.g., femtosecond pulses) in laser systems. Such pulses have an inherent minimum bandwidth required to support their extremely short pulse duration; the shorter the pulse, the more bandwidth is required. Summary of the Invention

[0003] This specification describes a wavelength stabilized narrow linewidth mode-locked picosecond laser system. The system includes a laser cavity comprising an amplifier, a mode-locking element, and a fiber Bragg grating acting as a narrow band reflector. The system includes a mount in which the fiber Bragg grating is mounted under tension, a tension control system for adjusting the tension, and a measurement device that provides a measurement output for use in wavelength stabilization of the laser system. A microcontroller or other controller wavelength stabilizes the laser by controlling the tension control system in response to the measurement output.

[0004] The techniques and systems described herein employ mode-locking to generate relatively long (≧1 ps) pulses with narrow linewidths that can be wavelength-stabilized in a feedback loop by controlling the tension of the fiber Bragg grating reflectors of the laser cavity, while sacrificing the possibility of femtosecond duration. This technique has been found to provide very stable narrow linewidth light sources in which the wavelength of the laser can be stabilized to within, for example, 5 or 10 picometers of the desired operating wavelength. Furthermore, because the described techniques use mode-locking and thus provide a pulsed output, they can be used to generate higher peak powers compared to other narrow linewidth systems that do not use the described techniques. In this way, a balance is struck between multiple interrelated factors to provide a laser that is particularly suitable for applications where high peak powers in a stable narrow linewidth are required. Such applications include frequency conversion in nonlinear crystals, particularly into the deep ultraviolet where variations in the laser wavelength on the order of 200 picometers can result in losses in efficiency.

[0005] The measured output may be related to a current operating wavelength of the fiber Bragg grating (FBG) (e.g., the measured output may be a measure of the current operating wavelength of the FBG). In some implementations, the measured output may be a measure of or related to the current operating wavelength of the laser system.

[0006] The FBG may have a uniform grating period, i.e., the FBG may not be chirped. The FBG mount may be formed from a positive thermal expansion material, such as aluminum, and the measurement device may include a temperature sensor configured to measure a temperature of at least a portion of the mount. Because the FBG is mounted in the mount, the longitudinal tension of the FBG depends on the degree of thermal expansion of the mount. Because the current operating wavelength of the fiber Bragg grating depends on its longitudinal tension, measuring the temperature of at least a portion of the mount provides a measurement output related to the current operating wavelength of the FBG. Thus, the temperature of at least a portion of the mount may be used as a feedback signal to stabilize the current operating wavelength of the FBG, thereby wavelength stabilizing the laser system.

[0007] Alternatively, the measurement device may include a spectrometer or other wavelength measurement device configured to measure the wavelength of the radiation generated (e.g., output) by the laser cavity. Because the FBG is narrowband, the wavelength of the radiation generated by the laser cavity is determined by, and is often the same as, the current operating wavelength of the FBG. Thus, measuring the wavelength of the radiation (e.g., output) generated by the laser cavity can provide a measured output related to the current operating wavelength of the FBG and thus may be used to wavelength stabilize the laser system. In some cases, nonlinear effects in the laser cavity may result in a change, e.g., a shift, between the FBG operating wavelength and the wavelength of the measured radiation. It will be appreciated that, despite this shift / offset, the measured wavelength is nevertheless related to the current operating wavelength of the FBG and thus may be used as a feedback signal to wavelength stabilize the laser system.

[0008] In some cases, a spectrometer or other wavelength measuring device may measure the wavelength of radiation downstream of the output of the laser cavity, for example, after nonlinear frequency conversion in one or more nonlinear elements. Even in this situation, it is understood that the measured wavelength is related to the current operating wavelength of the FBG, since the wavelength of the frequency converted radiation depends on the wavelength of the radiation generated by the laser system. Thus, measuring the wavelength of radiation downstream of the output of the laser cavity (e.g., after nonlinear frequency conversion in one or more nonlinear elements) can also provide a feedback signal for stabilizing the current operating wavelength of the FBG and therefore for wavelength stabilizing the laser system.

[0009] For example, UV radiation may be generated by providing one or more nonlinear elements after the laser system, which may be measured to provide a measured output related to the current operating wavelength of the fiber grating, thus providing a feedback signal for use in stabilizing the current operating wavelength of the laser system.

[0010] More generally, any measured output related to the current operating wavelength of the fiber Bragg grating may be used as a feedback signal for use in controlling a tension control system to wavelength stabilize the laser system.

[0011] The tension control system may be electronically controlled. In particular, the controller may be configured to receive a feedback signal derived from the measurement device and generate a responsive control signal for controlling the tension control system. It will be appreciated that the feedback signal may be based on (e.g., may include) the measurement output.

[0012] In one example, the tension control system comprises one or more temperature control devices configured to control the temperature of the mount. As the temperature of the mount changes, the mount thermally expands / contracts, thereby controlling the tension of the FBG attached to the mount. In some implementations, the tension control system may comprise a piezoelectric actuator configured to move one portion of the mount relative to another portion, thereby controlling the tension of the FBG. However, preferably, the tension control system comprises one or more temperature controllers for controlling the temperature of at least a portion of the mount, and does not comprise a piezoelectric element (e.g., a piezoelectric expander or other piezoelectric actuator). Advantageously, by providing a tension control system without a piezoelectric element, piezoelectric hysteresis and creep are avoided, thereby improving the long-term stability of the laser system. Piezoelectric creep can be regulated, for example, by using strain gauges, but this introduces additional complications that can be avoided by using temperature-based control.

[0013] In order that the invention may be more readily understood, embodiments thereof will now be described with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic diagram of an exemplary laser system. [Diagram 2] FIG. 2 shows the FBG mounting configuration of the laser system of FIG. 1 in more detail. [Diagram 3] FIG. 2 is a diagram showing the underside of the mount for the laser system of FIG. 1 and showing the temperature controller. [Figure 4] 1 is a schematic diagram of an exemplary laser system. [Diagram 5] FIG. 2 illustrates a control loop that may be implemented by the laser system controller. [Figure 6] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] 1-3 show an exemplary laser system 100 for producing a mode-locked train of picosecond pulses. As shown in Fig. 1, the laser system 100 comprises a linear laser cavity comprising an ytterbium-doped fiber amplifier 102, a mode-locking element in the form of a semiconductor saturable absorber mirror (SESAM) 104, and a fiber Bragg grating (FBG) 106. The FBG 106 is a narrowband reflective device that limits the linewidth of the laser system 100 and thus ensures that picosecond pulses of appropriate duration are output. For example, the linewidth of the laser system 100 may be less than 200 picometers. The pulses generated by the laser system 100 may have durations between 10 ps and 100 ps.

[0016] The FBG acts as a narrowband reflector around an operating wavelength that is determined by the longitudinal tension in the FBG 106. As will be appreciated by one of ordinary skill in the art, the operating wavelength of the laser system 100 (e.g., the center wavelength at which the laser system operates) depends on the operating wavelength of the FBG 106, which changes depending on the tension in the FBG 106.

[0017] The laser system 100 includes a tension control system that is used to prevent drift in the laser operating wavelength, which may occur due to environmental changes. With reference to FIG. 2, the FBG mount 108 may be formed from a positive thermal expansion material, such as aluminum. The mount 108 includes an elongated groove 110, and the FBG 106 is secured to the groove 110 under tension using an adhesive. The tension of the FBG 106 may be adjusted using one or more thermoelectric coolers (TECs) 112 disposed on the underside of the aluminum mount 108, as shown in FIG. 3. It will be appreciated that the TECs 112 may be used to heat and cool the mount in response to an electrical control signal. An increase in temperature of the TECs heats the aluminum mount 108, causing it to expand. Since the FBG 106 is secured to the mount 108, and the expansion of the mount 108 is partially in the longitudinal direction of the FBG, thermal expansion of the mount increases the tension of the FBG. Similarly, as the temperature of the TEC decreases, the aluminum cools to a lower temperature and therefore contracts, thereby reducing the tension in the FBG. During fabrication, the FBG may be fixed in the mount 108 under tension while the temperature of the aluminum mount is maintained at a selected value, and during operation this allows the tension in the FBG to be adjusted by varying the temperature above and below this selected value.

[0018] 1, the TEC 112 comprises a Peltier device that can be heated or cooled in response to an electrical signal provided by a controller 114. The controller 114 includes a microcontroller and may additionally include suitable electronics, for example, to amplify a temperature control signal 115 to an appropriate level for controlling the temperature of the TEC.

[0019] As shown, a measurement device in the form of a temperature sensor 116 is positioned on the aluminum mount to measure the temperature of the aluminum mount. A controller 114 is configured to receive a feedback signal 117 derived from the temperature sensor 116 and wavelength stabilize the laser by adjusting a temperature control signal 115 to heat or cool the aluminum mount in response to the feedback signal 117. More specifically, the controller comprises one or more processors configured to operate according to computer readable instructions to execute a feedback loop, which adjusts the temperature control signal to ensure that the measured temperature of the aluminum mount, as determined by the feedback signal 117, is maintained at a selected level, e.g., within a predetermined tolerance range.

[0020] By maintaining the temperature of the aluminum mount at a selected level, the tension in the FBG is also maintained, thereby stabilizing the operating wavelength of the FBG, and therefore the operating wavelength of the laser system 100.

[0021] The operating wavelength of the laser system 100 may be more coarsely tuned by varying the temperature of the mount 108 using the TEC 112 until the desired operating wavelength is achieved. To identify when the laser has been tuned to the desired wavelength, the wavelength may be measured using a spectrometer or inferred from the temperature of the mount as measured by the temperature sensor 116. In particular, a suitable calibration may be performed to determine the relationship between the measured temperature and the operating wavelength of the laser (a roughly linear relationship is expected).

[0022] Once the laser system 100 is tuned to the desired wavelength, it is stabilized at the desired operating wavelength using the wavelength stabilization feedback loop described above. In this manner, stable operation can be achieved at any desired wavelength within the ytterbium gain band, for example, any wavelength between 1020 nm and 1080 nm. It has been found that the techniques described herein allow for stabilization of the operating wavelength of the laser to within, for example, 10%, 5% or 1% of the spectral linewidth. In some examples, the wavelength may be stabilized to within 10 picometers or 5 picometers of the desired operating wavelength.

[0023] 4 shows a more general schematic diagram of an exemplary wavelength-stabilized narrow-linewidth mode-locked picosecond laser system 400. The laser system 400 comprises a laser cavity comprising an amplifier 410, a mode-locking element 420, and a fiber Bragg grating (FBG) 430 acting as a narrow-band reflector. The laser system 400 further comprises a mount 440 in which the FBG 430 is mounted under tension, a tension control system configured to adjust the tension of the FBG 430, a measurement device 450 that provides a measurement output related to the current operating wavelength of the FBG 430, and a controller 460 that wavelength-stabilizes the laser by controlling the tension control system in response to the measurement output.

[0024] The amplifier may include an ytterbium-doped fiber amplifier as described above in connection with Figures 1-3, or may include another type of fiber amplifier, such as an erbium-doped fiber amplifier (EDFA), a thulium-doped fiber amplifier, a holmium-doped fiber amplifier, or a praseodymium-doped fiber amplifier. Additionally, bulk amplifiers may be used instead of fiber amplifiers. The laser cavity may include multiple amplifiers of the same or different types, e.g., amplifier chains.

[0025] The mode-locking element 420 may include a suitable passive mode-locking element, such as a saturable absorber, e.g., a semiconductor saturable absorber mirror (SESAM), as described above in connection with FIGS. 1-3. In some examples, for example when a SESAM is used, the mode-locking element may also act as a reflector 425 that forms a laser cavity with the FBG 430. However, instead, a separate reflector may be provided to form a cavity with the FBG 430. In some examples, the mode-locking element 420 may include an active element rather than a passive element. For example, the mode-locking element 420 may include a modulator, such as an electro-optic or acousto-optic modulator, driven by a periodic electrical signal to cause mode-locking of the laser system 400.

[0026] The FBG 430 may be approximately uniform, e.g., the grating period and / or the refractive index modulation may vary by less than 50%, such as less than 25%, such as less than 10%, such as less than 1%, along the length of the grating. As will be appreciated by one of ordinary skill in the art, the refractive index modulation of the FBG may be set to obtain a desired bandwidth of the grating, and the length of the grating may be used to set the peak reflectivity. The FBG acts as a reflector near an operating wavelength (e.g., a central wavelength) determined by the grating period. The grating period may be changed by changing the longitudinal tension of the FBG, thereby tuning the operating wavelength of the FBG. The operating wavelength of the FBG may include the wavelength at which the spectral response of the FBG has its peak.

[0027] Unless otherwise stated, the peak reflectance, also referred to as reflectance, may be 99% or less, such as 80% or less, such as 70% or less, such as 60% or less, such as 50% or less, such as 40% or less, such as 30% or less, such as 20% or less, such as 10% or less. The reflectance may be 5% or more, such as 10% or more, such as 20% or more, such as 30% or more, such as 40% or more, such as 50% or more, such as 60% or more, such as 70% or more, such as 80% or more, such as 90% or more, such as 99% or more. In one embodiment, the reflectance is between 80% and 100%, such as 99%. In one embodiment, the reflectance is between 70% and 80%, such as 75%. In one embodiment, the reflectance is between 10% and 25%, such as 15%.

[0028] The width of the FBG spectral response may be less than 1000 picometers, such as less than 500 picometers, such as less than 200 picometers, such as less than 100 picometers. The tension control system is configured to increase or decrease tension in the FBG 430 in response to an electrical signal derived from the controller 460. The tension control system may be, for example, a temperature-based system as described above in relation to Figures 1-3, which controls the temperature of at least a portion of the mount such that the mount adjusts the tension of the FBG 430 by thermally expanding or contracting. Alternatively, however, the FBG may be attached to an actuator that can be used to adjust the tension of the FBG 430, for example, by piezoelectrically actuated movement of one portion of the mount relative to another portion.

[0029] The mount 440 may comprise any suitable material. For temperature-based tension control, the mount may comprise any suitable positive thermal expansion material, such as aluminum or a ceramic material. The mount 440 may comprise a substrate and a holder to which the FBG is glued in place. One or more temperature controllers may be provided to control the temperature of the mount to cause thermal expansion or contraction of the mount (or at least a portion thereof) and thereby adjust the tension of the fiber Bragg grating. Alternatively, if piezoelectric tension control is used, the mount may comprise an actuator comprising a suitable piezoelectric element that moves the mounting point of one FBG 430 relative to another mounting point in response to an electrical signal derived from the controller 440. In some cases, both temperature-based control and piezoelectric tension control may be used to achieve improved control of the tension of the FBG 430 and therefore the operating wavelength of the laser system 400. However, preferably, the laser system does not comprise a piezoelectric element and one or more temperature controllers are used to control the temperature of the mount. In this way, piezoelectric hysteresis and creep can be avoided. Piezoelectric creep can be regulated, for example, by using strain gauges, but this introduces additional complications that can be avoided by using exclusively temperature-based control.

[0030] The measurement device 450 provides a measurement output related to the current operating wavelength of the FBG 430. The measurement device 450 may comprise a temperature sensor that measures the temperature of the mount 440, for example as described above in relation to Figures 1-3. In this case, the temperature of the mount is related to the operating wavelength of the FBG 430, since the tension in the FBG 430 depends on the extent to which the mount has thermally expanded or contracted, and the operating wavelength of the FBG depends on that tension. In particular, an approximately linear relationship is expected between the temperature of the mount and the FBG operating wavelength.

[0031] However, instead, the measurement device 450 may be configured to directly measure the operating wavelength of the laser system 400. For example, the measurement device 450 may include a spectrometer that receives a portion of the radiation generated by the laser cavity (e.g., via a tap coupler) and measures its wavelength, which can then be equated to the current operating wavelength of the FBG 430. More generally, any measurement related to the current operating wavelength of the FBG 430 or the laser system 400 may be used for wavelength stabilization purposes.

[0032] The controller 460 may comprise a microcontroller or other data processing device. The controller 460 comprises one or more processors and a memory that stores computer-readable instructions that, when executed by the processor, cause the processor to perform one or more operations. FIG. 5 illustrates a wavelength stabilization procedure 500 that may be performed by the controller 460. As shown, the controller receives a measurement signal (e.g., a feedback signal) derived from the measurement device 450 (510). The controller 460 determines whether the measurement signal indicates that the current operating wavelength of the FBG 430 has deviated from the desired wavelength by more than a threshold amount (520). If so, the controller 460 sends a control signal to the tension control system to cause the tension control system to adjust the tension of the FBG 430 to move the current operating wavelength of the FBG 430 toward the desired wavelength (i.e., by increasing or decreasing the tension appropriately) (530). Process 500 may be performed continuously during operation of laser system 400 to maintain the operating wavelength of laser system 400 at the desired wavelength with high stability, for example within 10 pm or within 5 pm of the desired wavelength.

[0033] The controller 460 may also be used to tune the current operating wavelength of the laser system 400 to another design wavelength by adjusting the tension control system until the measurement signal indicates that the current operating wavelength of the FBG 430 corresponds to the desired wavelength. Once the laser system 400 is tuned to the desired wavelength, it may be stabilized at this desired operating wavelength using a wavelength stabilization procedure 500 shown in Figure 5. In this manner, tunable wavelength stabilized operation may be achieved using the laser system 400.

[0034] In various implementations, pulses generated by the laser systems described herein may have durations longer than 1 ps, for example longer than 10 ps, ​​or longer than 20 ps.

[0035] In various implementations, the pulses generated by the laser systems described herein may have durations of less than 100 ps, ​​such as less than 60 ps or less than 50 ps. In some examples, the laser systems may generate pulses having durations between 30 ps and 60 ps. The pulse duration may be measured based on a full width at half maximum (FWHM) measurement.

[0036] In various implementations, the peak power generated by the laser systems described herein can be greater than 1 kW, such as greater than 10 kW or greater than 15 kW. The laser system described herein may be used to achieve efficient frequency conversion in nonlinear elements such as nonlinear crystals. As will be appreciated by those skilled in the art, using appropriate frequency conversion configurations, various wavelengths of interest for specific applications may be reached, for example, conversion from about 1 micrometer to ultraviolet or deep ultraviolet (e.g., less than 300 nm) is possible using such techniques.

[0037] It is important to note that the system 100, 400 combines several properties that work together to achieve high efficiency in frequency conversion, particularly narrow linewidth, wavelength stability, and pulsed operation. Narrow linewidths result in efficient frequency conversion due to phase matching constraints, since typically only narrow linewidths can be converted and any energy outside the phase matching bandwidth remains unconverted. Although narrow linewidths can be achieved using CW lasers, pulsed operation results in higher peak powers and therefore higher efficiency of conversion. Wavelength stability also leads to efficiency, since any variation in the laser wavelength can result in efficiency losses. For example, in conversion to the deep ultraviolet, a variation in the laser wavelength of only 200 picometers can result in efficiency losses.

[0038] FIG. 6 shows a frequency conversion configuration 600 using one or more of the wavelength-stabilized narrow-linewidth mode-locked picosecond laser systems 100, 400 described above. As shown, picosecond pulses from the laser system 100, 400 are launched (e.g., using appropriate optics) into one or more nonlinear elements 610 (e.g., one or more nonlinear crystals), where they undergo frequency conversion by one or more nonlinear effects, such as harmonic generation (e.g., second harmonic generation). In some examples, the frequency-converted light generated in one nonlinear element may be combined with unconverted light (or light generated in a third nonlinear element) in a second nonlinear element to generate additional wavelengths, for example, using sum frequency generation, difference frequency generation, or parametric frequency conversion. In some cases, the output of two or more wavelength-stabilized narrow-linewidth mode-locked picosecond laser systems may be combined together in the nonlinear elements of the frequency conversion configuration, thereby further expanding the possibilities of the wavelengths that can be generated.

[0039] The wavelength-stabilized laser system as described herein may also be used to provide a stable seed source in a larger laser system that uses amplification in a solid-state crystal. This is particularly advantageous when the solid-state crystal includes a Nd:YAG crystal or another solid-state crystal with limited gain bandwidth, because in such a case, any wavelength fluctuation of the seed may result in a loss of efficiency. For example, a wavelength-stabilized laser system operating at 1064.35 nm may be used as a seed in a larger (e.g., bulk) laser system that uses amplification in a Nd:YAG crystal.

[0040] The wavelength-stabilized laser system described herein may also be used as or as part of a seed source of a chirped pulse amplification (CPA) system. For example, the CPA system may include a pulse source (e.g., seed source) including a wavelength-stabilized laser, a pulse stretcher, one or more optical amplifiers, and a pulse compressor. In operation, a short pulse generated by the pulse source (e.g., seed source) passes along an optical path where the pulse is stretched in time (i.e., stretched in time) by the stretcher, amplified by one or more optical amplifiers, and then compressed in time by the pulse compressor. The pulse stretcher is configured to stretch the pulse in time to reduce the peak power of the pulse and thus avoid or reduce nonlinear effects occurring in the one or more optical amplifiers. The one or more optical amplifiers are disposed downstream of the pulse stretcher along the optical path and configured to amplify the pulse stretched by the pulse stretcher. The pulse compressor is disposed downstream of the one or more amplifiers along the optical path and configured to generate a high peak power pulse at the output of the system by compressing the pulse amplified by the one or more amplifiers. Various specific possibilities for the components of the stretcher, amplifier and compressor are known per se to those skilled in the art and will not be described in detail here. For example, the stretcher may comprise a circulator configured to direct the pulse to a fiber Bragg grating that stretches the pulse, and / or may comprise a length of dispersive fiber and / or a bulk transmission or reflection grating in a suitable optical arrangement. The one or more amplifiers may include one or more optical fiber amplifiers (e.g., one or more ytterbium, erbium, thulium, holmium, or praseodymium doped amplifiers) and may be arranged in an amplifier chain including an optical preamplifier and a power amplifier. The pulse compressor may comprise, for example, a transmission grating and / or a reflection grating in a suitable optical arrangement and in some cases a fiber-based compressor.In some implementations, the pulse compressor may be omitted, i.e., the CPA system may include a pulse source (eg, a seed source), a stretcher, and one or more optical amplifiers.

[0041] This specification also includes the subject matter of the following sections: 1. A wavelength-stabilized narrow-linewidth mode-locked picosecond laser system comprising: 1. A laser cavity, comprising: An amplifier; A mode-locking element; a fiber Bragg grating acting as a narrowband reflector; a mount in which the fiber Bragg grating is mounted under tension; a tension control system for adjusting the tension of the fiber Bragg grating; a measurement device for providing a measurement output related to a current operating wavelength of the fiber Bragg grating; a controller for wavelength stabilizing the laser by controlling the tension control system in response to the measurement output, the controller being configured to receive a feedback signal derived from the measurement device and generate a responsive control signal for electrically controlling the tension control system.

[0042] 2. The laser system of item 1, wherein the tension control system comprises a temperature controller for controlling the temperature of at least a portion of the mount and causing thermal expansion or contraction of at least a portion of the mount, thereby adjusting the tension of the fiber Bragg grating.

[0043] 3. The laser system of item 2, wherein the at least a portion of the mount comprises aluminum. 4. The laser system of any one of items 1 to 3, wherein the measurement device includes a temperature sensor configured to measure a temperature of at least a portion of the mount.

[0044] 5. The laser system of any one of items 1 to 3, wherein the measurement device is configured to measure a wavelength of radiation generated using the laser cavity. 6. The laser system of any one of items 1-5, wherein the laser cavity is configured to provide pulses having a duration of less than 100 picoseconds, the pulses have a duration between 30 picoseconds and 60 picoseconds, or both.

[0045] 7. The laser system of any one of items 1 to 6, wherein the laser has a spectral linewidth of less than 200 picometers. 8. The laser system of any one of items 1 to 7, wherein the controller is configured to stabilize the operating wavelength of the laser to within 10% or less of the spectral linewidth of the laser, such as within 5% or less of the spectral linewidth of the laser, such as within 1% or less of the spectral linewidth of the laser.

[0046] 9. The laser system of any one of items 1-8, wherein the controller is configured to stabilize the operating wavelength of the laser to within 10 picometers or less of a desired operating wavelength, or to stabilize the operating wavelength of the laser to within 5 picometers or less of a desired operating wavelength.

[0047] 10. The laser system of any one of items 1 to 9, wherein the amplifier includes an ytterbium fiber amplifier and the operating wavelength of the laser is between 1020 nm and 1080 nm.

[0048] 11. A wavelength-stabilized laser system according to any one of items 1 to 10, and a frequency converter for converting the operating wavelength of the laser system to a converted wavelength.

[0049] 12. The apparatus of item 11, wherein the frequency converter includes one or more nonlinear frequency conversion crystals. 13. The apparatus of item 11 or 12, wherein the frequency converter is configured to convert the operating wavelength of the wavelength-stabilized laser system to a wavelength shorter than 300 nm.

[0050] 14. The wavelength stabilized laser system according to any one of items 1 to 10, a solid state crystal configured to amplify radiation generated using the wavelength stabilized laser system.

[0051] 15. The laser system of item 14, wherein the solid crystal comprises a Nd:YAG crystal. 16. A chirped pulse amplification (CPA) system comprising: A pulse source comprising any one of the wavelength-stabilized laser systems according to items 1 to 10; a pulse stretcher configured to stretch in time a pulse generated by the pulse source; one or more optical amplifiers for amplifying pulses stretched by the pulse stretcher; an optical compressor that temporally compresses pulses amplified by the one or more optical amplifiers.

[0052] Many modifications and variations of the system and techniques described herein will be apparent to those of ordinary skill in the art.

Claims

1. 1. A wavelength-stabilized narrow-linewidth mode-locked picosecond laser system comprising:

1. A laser cavity comprising: An amplifier; A mode-locking element; a fiber Bragg grating acting as a narrowband reflector; a mount in which the fiber Bragg grating is mounted under tension; a tension control system for adjusting the tension of the fiber Bragg grating; a measurement device for providing a measurement output related to the current operating wavelength of the fiber Bragg grating; a controller for wavelength stabilizing the laser system by controlling the tension control system in response to the measurement output, the controller being configured to receive a feedback signal derived from the measurement device and generate a responsive control signal for electrically controlling the tension control system; The tension control system comprises one or more temperature control devices for controlling a temperature of at least a portion of the mount and causing thermal expansion or contraction of the at least a portion of the mount, thereby adjusting the tension of the fiber Bragg grating.

2. 10. The laser system of claim 1, wherein the tension control system does not include a piezoelectric element.

3. 10. The laser system of claim 1, wherein said at least a portion of said mount comprises aluminum.

4. 10. The laser system of claim 1, wherein the measurement device comprises a temperature sensor configured to measure a temperature of at least a portion of the mount.

5. 10. The laser system of claim 1, wherein the measurement device is configured to measure a wavelength of radiation generated using the laser cavity.

6. 10. The laser system of claim 1, wherein the laser cavity is configured to provide pulses having a duration of less than 100 picoseconds.

7. The laser system of claim 6, wherein the pulse has a duration between 30 picoseconds and 60 picoseconds.

8. 10. The laser system of claim 1, wherein the laser system has a spectral linewidth of less than 200 picometers.

9. 10. The laser system of claim 1, wherein the controller is configured to stabilize the operating wavelength of the laser system to within 10% or less of a spectral linewidth of the laser system.

10. The laser system of claim 9, wherein the controller is configured to stabilize the operating wavelength of the laser system to within 5% or less of the spectral linewidth of the laser system.

11. The laser system of claim 10, wherein the controller is configured to stabilize the operating wavelength of the laser system to within 1% or less of the spectral linewidth of the laser system.

12. 10. The laser system of claim 1, wherein the controller is configured to stabilize the operating wavelength of the laser system to within 10 pm or less of a desired operating wavelength.

13. The laser system of claim 12, wherein the controller is configured to stabilize the operating wavelength of the laser system to within 5 picometers or less of a desired operating wavelength.

14. 10. The laser system of claim 1, wherein the amplifier comprises an ytterbium fiber amplifier and the operating wavelength of the laser system is between 1020 nm and 1080 nm.

15. The laser system of claim 1, further comprising a frequency converter for converting the operating wavelength to a converted wavelength.

16. 16. The laser system of claim 15, wherein the frequency converter comprises one or more nonlinear frequency conversion crystals.

17. 16. The laser system of claim 15, wherein the frequency converter is configured to convert the operating wavelength of the laser system to a wavelength shorter than 300 nm.

18. A laser system comprising:

1. A wavelength stabilized laser system, comprising:

1. A laser cavity comprising: An amplifier; A mode-locking element; a fiber Bragg grating acting as a narrowband reflector; a mount in which the fiber Bragg grating is mounted under tension; a tension control system for adjusting the tension of the fiber Bragg grating; a measurement device for providing a measurement output related to the current operating wavelength of the fiber Bragg grating; a controller for wavelength stabilizing the laser system by controlling the tension control system in response to the measurement output; a solid-state crystal configured to amplify radiation generated using the wavelength-stabilized laser system.

19. 20. The laser system of claim 18, wherein the solid state crystal comprises a Nd:YAG crystal.

20. A chirped pulse amplification (CPA) system, comprising:

1. A pulse source comprising a wavelength stabilized laser system, the wavelength stabilized laser system comprising:

1. A laser cavity comprising: An amplifier; A mode-locking element; a fiber Bragg grating acting as a narrowband reflector; a mount in which the fiber Bragg grating is mounted under tension; a tension control system for adjusting the tension of the fiber Bragg grating; a measurement device for providing a measurement output related to the current operating wavelength of the fiber Bragg grating; a controller for wavelength stabilizing the laser system by controlling the tension control system in response to the measurement output; a pulse stretcher configured to stretch in time pulses generated by the pulse source; one or more optical amplifiers for amplifying pulses stretched by the pulse stretcher; a pulse compressor for temporally compressing pulses amplified by the one or more optical amplifiers.

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