Ultra-fast laser system for ophthalmology applications

Abstract

The present disclosure relates to a laser system comprising: a mode-locked oscillator or laser configured for generating seed laser pulses; a nonlinear crystal configured for frequency doubling the seed laser pulses from the oscillator, whereby modified laser pulses are obtained; a pulse stretcher, such as a chirped fiber-Bragg grating (CFBG), configured for temporally stretching the modified laser pulses, whereby stretched laser pulses are obtained; a regenerative amplifier configured for amplifying the stretched laser pulses, whereby amplified laser pulses are obtained, wherein the regenerative amplifier comprises a gain crystal selected from the group of chromium-doped Colquiriite crystals (Cr:Colquiriites) and Alexandrite crystals; and a compressor for temporally compressing the amplified laser pulses, whereby compressed pulses are obtained.

Description

[0001] ULTRA-FAST LASER SYSTEM FOR OPHTHALMOLOGY APPLICATIONS

[0002] Technical field

[0003] The present disclosure relates to a laser system. In particular, the present disclosure relates to a laser system for applications within ophthalmology, ultrafast spectroscopy, multiphoton microscopy, and / or materials processing.

[0004] Background

[0005] Laser technology has revolutionized numerous fields, offering powerful tools for various applications. Traditional laser systems, including continuous-wave lasers and pulsed lasers, have been instrumental in advancing fields such as ophthalmology, ultrafast spectroscopy, multiphoton microscopy, materials processing, and laser surgery. However, these systems often face challenges such as limited precision, thermal effects, and lack of versatility.

[0006] In ophthalmology, existing laser systems may pose risks of tissue damage and limited precision, impacting surgical outcomes. Similarly, in ultrafast spectroscopy and multiphoton microscopy, precise control over laser parameters is crucial for accurate measurements and imaging. Moreover, in materials processing and laser surgery, the ability to deliver high-energy pulses with minimal thermal effects is essential for achieving desired results.

[0007] In response to these challenges, there is a need for a laser system that can provide improvements, such as enhanced precision, versatility, or safety, across various applications, including ophthalmology, ultrafast spectroscopy, multiphoton microscopy, materials processing, and laser surgery. This new laser system should ideally address the limitations of existing technologies and offer improved efficacy and outcomes in diverse fields.

[0008] Summary

[0009] The above-mentioned challenges are solved by providing a laser system comprising: a seed laser, such as a mode-locked oscillator, configured for generating seed laser pulses; a nonlinear crystal configured for frequency doubling the seed laser pulses from the oscillator, whereby modified laser pulses are obtained; a pulse stretcher configured for temporally stretching the modified laser pulses, whereby stretched laser pulses are obtained; a regenerative amplifier configured for amplifying the stretched laser pulses, whereby amplified laser pulses are obtained, wherein the regenerative amplifier comprises a gain medium, such as a gain crystal selected from the group of chromium-doped Colquiriite crystals (CrColquiriites) or Alexandrite crystals; and wherein the laser system comprises a compressor for temporally compressing the amplified laser pulses, whereby compressed pulses are obtained. The compressed pulses may be output by the laser system and used for e.g. ophthalmology applications, ultrafast spectroscopy, multiphoton microscopy, and / or materials processing.

[0010] In accordance with some embodiments, the laser system comprises a mode-locked oscillator, such as an Er-doped mode-locked oscillator, configured for generating seed laser pulses; a nonlinear crystal configured for frequency doubling the seed laser pulses from the oscillator, whereby modified laser pulses are obtained; a pulse stretcher, such as a chirped fiber-Bragg grating (CFBG), configured for temporally stretching the modified laser pulses, whereby stretched laser pulses are obtained; a regenerative amplifier configured for amplifying the stretched laser pulses, whereby amplified laser pulses are obtained, wherein the regenerative amplifier comprises a gain medium, such as a gain crystal selected from the group of chromium-doped Colquiriite crystals (CrColquiriites); and a compressor for temporally compressing the amplified laser pulses, whereby compressed pulses are obtained.

[0011] In accordance with some embodiments, the laser system comprises a mode-locked oscillator, such as an Er-doped mode-locked oscillator, configured for generating seed laser pulses having a central wavelength between 1500 nm and 1600 nm, such as between 1520 nm and 1580 nm; a nonlinear crystal configured for frequency doubling the seed laser pulses from the oscillator, whereby modified laser pulses having a central wavelength between 750 nm and 800 nm, such as between 760 nm and 790 nm are obtained; a pulse stretcher, such as a chirped fiber-Bragg grating (CFBG), configured for temporally stretching the modified laser pulses, whereby stretched laser pulses are obtained; a regenerative amplifier configured for amplifying the stretched laser pulses, whereby amplified laser pulses are obtained, wherein the regenerative amplifier comprises a gain medium, such as a gain crystal selected from the group of chromium-doped Colquiriite crystals (CrColquiriites); and a compressor for temporally compressing the amplified laser pulses, whereby compressed pulses are obtained.

[0012] In accordance with some embodiments, the laser system comprises: a mode-locked laser, such as a solid-state mode-locked laser, for generating seed laser pulses, wherein the laser comprises a chromium-doped Colquiriite crystal; a pulse stretcher, such as a chirped fiber-Bragg grating (CFBG), configured for temporally stretching the seed laser pulses, whereby stretched laser pulses are obtained; a regenerative amplifier configured for amplifying the stretched laser pulses, whereby amplified laser pulses are obtained, wherein the regenerative amplifier comprises a gain medium, such as a gain crystal selected from the group of CrColquiriites; and a compressor for temporally compressing the amplified laser pulses, whereby compressed pulses are obtained. In accordance with some embodiments, the laser system comprises: a solid-state mode- locked laser for generating seed laser pulses having a central wavelength of between 700 nm and 800 nm, such as between 750 nm and 790 nm, wherein the laser comprises a chromium- doped Colquiriite crystal, such as LiCaAIFe (LiCAF); a pulse stretcher, such as a chirped fiber- Bragg grating (CFBG), configured for temporally stretching the seed laser pulses, whereby stretched laser pulses are obtained; a regenerative amplifier configured for amplifying the stretched laser pulses, whereby amplified laser pulses are obtained, wherein the regenerative amplifier comprises a gain medium, such as a gain crystal selected from the group of CrColquiriites, such as LiCAF; and a compressor for temporally compressing the amplified laser pulses, whereby compressed pulses are obtained.

[0013] The present disclosure further relates to a method of generating ultrashort laser pulses for ophthalmology applications, the method comprising the steps of: providing seed laser pulses having a central wavelength between 1500 nm and 1600 nm, such as between 1520 nm and 1580 nm; frequency doubling the seed laser pulses through second-harmonic generation (SHG), whereby modified laser pulses having a central wavelength between 700 nm and 800 nm, such as between 750 nm and 790 nm, are obtained; temporally stretching the modified laser pulses, whereby stretched laser pulses are obtained; amplifying the stretched laser pulses, whereby amplified laser pulses are obtained, wherein the laser pulses are amplified by a gain medium, such as a gain crystal selected from the group of chromium- doped Colquiriite crystals (CrColquiriites); temporally compressing the amplified laser pulses, whereby compressed pulses are obtained, wherein said compressed pulses have a pulse duration in the femtosecond range, such as a pulse duration of between 10 fs and 100 fs.

[0014] The present disclosure further relates to a method of generating ultrashort laser pulses for ophthalmology applications, the method comprising the steps of: providing seed laser pulses having a central wavelength between 700 nm and 800 nm, wherein said seed laser pulses are generated by a chromium-doped Colquiriite crystal; temporally stretching the seed laser pulses, whereby stretched laser pulses are obtained; amplifying the stretched laser pulses, whereby amplified laser pulses are obtained, wherein the laser pulses are amplified by a gain medium, such as a gain crystal selected from the group of chromium-doped Colquiriite crystals (CrColquiriites); temporally compressing the amplified laser pulses, whereby compressed pulses are obtained. The compressed pulses may have a pulse duration in the femtosecond range, such as a pulse duration of between 10 fs and 100 fs.

[0015] The disclosed laser system provides a number of advantages over existing laser systems, such as being more cost effective, e.g. being cheaper to manufacture and / or cheaper to replace in service repairs. Furthermore, the disclosed laser system provides improvements in terms of thermal properties and stability, such as improved thermal lensing. Additionally, the laser pulses output by the disclosed laser system are particularly suitable for applications such as ophthalmology, ultrafast spectroscopy, multiphoton microscopy, and / or materials processing.

[0016] Brief description of the drawings

[0017] Fig. 1 shows an embodiment of a laser system according to the present disclosure.

[0018] Fig. 2 shows another embodiment of a laser system according to the present disclosure.

[0019] Fig. 3 shows yet another embodiment of a laser system according to the present disclosure.

[0020] Detailed description

[0021] A better understanding of the features and advantages of the present disclosure will be obtained by reference to the following detailed description and the accompanying drawings.

[0022] The laser system may comprise a seed laser for generating seed laser pulses. The seed laser may be a short-pulse oscillator, such as a mode-locked oscillator, configured for generating ultrashort seed laser pulses, such as laser pulses having a pulse duration in the femtosecond or picosecond range. In particular, the seed laser pulses may have a pulse duration in the femtosecond range, such as a pulse duration of between 1 fs and 1000 fs, such as between 10 fs and 450 fs, such as between 50 fs and 300 fs. The laser system may be configured for generating a train of output laser pulses at a pulse repetition rate of between 20 kHz and 1000 kHz, such as between 100 kHz and 500 kHz, such as between 200 kHz and 300 kHz. The aforementioned pulse durations and pulse repetition rates may be suitable for applications such as ophthalmology, ultrafast spectroscopy, multiphoton microscopy, micro machining, and / or materials processing. The seed laser may be configured for providing a fixed pulse repetition rate or a variable pulse repetition rate. The pulse repetition rate provided by the seed laser may be higher than the repetition rate of the output laser pulses. As an example, the seed laser may be configured for generating a train of seed laser pulses at a pulse repetition rate of between 1 MHz and 100 MHz, such as between 10 MHz and 80 MHz. In some cases, the repetition rate is between 1 MHz and 56 MHz.

[0023] The seed laser may comprise a laser resonator for housing an optical crystal. The laser resonator may further comprise one or more dispersion compensation elements, such as one or more Gires-Tournois interferometer mirrors (GTI). These dispersion compensation elements may be configured to compensate for the group-velocity dispersion (GVD) of the laser pulses resonant in the laser resonator. In particular, this is relevant in case the seed laser is a solid-state laser configured for providing a variable pulse repetition rate. Alternatively, in case the seed laser is a fiber-based oscillator, the laser resonator may be defined by one or more optical components, such as fiber-Bragg gratings (FBG), semiconductor saturable absorber mirrors (SESAM), and / or combinations thereof.

[0024] The seed laser may be a solid-state laser, or it may be a fiber-based laser. Advantageously, the seed laser is a fiber-based mode-locked laser. Some advantages of utilizing a fiber-based seed laser are that they are more production-friendly and servicefriendly than solid-state based lasers. Another advantage is that a fiber-based laser is typically cheaper to produce and also cheaper to replace.

[0025] In some embodiments, the seed laser is a mode-locked laser. The seed laser may comprise a gain material doped with a rare-Earth element, such as Erbium or Ytterbium. In some embodiments, the seed laser is configured for generating seed laser pulses having a central wavelength in the range from about 1400 nm to about 1600 nm, such as from about 1500 nm to about 1600 nm. In some embodiments, the seed laser is an Erbium-doped (Er- doped) mode-locked laser for generating seed laser pulses having a central wavelength between 1520 nm and 1580 nm, such as between 1540 nm and 1560 nm. At least some advantages of using an Er-doped seed laser are its stability, reliability, and ability to produce pulses in the femtosecond regime. The laser system may further comprise a nonlinear crystal arranged downstream of the seed laser, wherein said nonlinear crystal is configured to receive and frequency convert the seed laser pulses.

[0026] In some embodiments, the seed laser is a solid-state mode-locked laser, wherein the laser comprises a gain medium selected from the group of chromium-doped colquiriite crystals, such as CrLiCAF, CrLiSAF, CrLiSrAIFe and CrLiSrGaFe, or CrLiSGaF. One particularly useful example for generating laser pulses having a wavelength of approximately 780 nm is a solid-state mode-locked laser comprising a CrLiCAF crystal. Accordingly, the seed laser pulses generated by such a CrLiCAF mode-locked laser may have a central wavelength between 760 nm and 790 nm, such as between 770 nm and 785 nm. In that case, no frequency conversion of the seed laser pulses is needed.

[0027] The seed laser pulses may be provided as input to a nonlinear crystal for performing frequency conversion of the seed laser pulses. The seed laser may be arranged upstream of the nonlinear crystal.

[0028] The laser system may comprise a nonlinear crystal configured for converting the frequency of the seed laser pulses generated by the seed laser. In particular, the nonlinear crystal may be configured for frequency doubling the seed laser pulses, whereby frequency doubled laser pulses are obtained. The frequency doubling may be achieved via second harmonic generation (SHG). Thus, the nonlinear crystal may be configured for frequency conversion through second harmonic generation (SHG). As an example, if the seed laser pulses have a central wavelength of about 1560 nm, then the frequency doubled laser pulses would have a central wavelength of about 780 nm. Other wavelengths can be envisaged without departing from the scope and teaching of the present disclosure. The nonlinear crystal may be arranged downstream of the seed laser, such as arranged between the seed laser and a pulse stretcher forming part of the laser system.

[0029] In some embodiments, the nonlinear crystal is selected from the group of Periodically Poled Lithium Niobate (PPLN), Bismuth Borate (BiBo), Beta Barium Borate (BBO), Lithium Triborate (LBO), or Potassium Dihydrogen Phosphate (KDP). The frequency converted laser pulses output from the nonlinear crystal may also be referred to as modified laser pulses. The modified laser pulses may be provided as input to a pulse stretcher for temporally stretching said modified laser pulses.

[0030] The laser system may comprise a pulse stretcher configured for temporally stretching the modified, or frequency doubled, laser pulses, whereby stretched laser pulses are obtained. The pulse stretcher may be arranged downstream of the nonlinear crystal, such as between the nonlinear crystal and one or more optical amplifiers. The pulse stretcher may comprise one or more components selected from the group of: diffraction gratings, Bragg gratings, chirped volume-Bragg gratings, chirped fiber-Bragg gratings (CFBG), prisms, grisms, and / or combinations thereof.

[0031] In some embodiments, the pulse stretcher is a chirped fiber-Bragg grating (CFBG). This is particularly useful in case the seed laser is a fiber-based seed laser, such as a mode-locked fiber laser. In other embodiments, the pulse stretcher is an integral part of the nonlinear crystal, such that said nonlinear crystal is configured to perform both frequency conversion and temporal stretching of the laser pulses. An example of a nonlinear crystal suitable for such a purpose is a Chirped Periodically Poled Lithium Niobate (CPPLN) crystal. In that case, the seed laser may be a solid-state mode-locked laser.

[0032] In some embodiments, the pulse stretcher is a tunable pulse stretcher. Accordingly, in some cases the dispersion of the pulse stretcher may be tuned / adjusted. Thus, the pulse stretcher may be tunable such that 2ndand / or 3rdorder dispersion of the modified pulses can be adjusted. In some cases, 4thorder dispersion may also be adjusted by the tunable pulse stretcher. This may be achieved by utilizing a tunable CFBG. As an example, the CFBG may be provided with a temperature control for adjusting the dispersion via the temperature. In some embodiments, the pulse stretcher is configured to at least partially compensate for 2nd order dispersion. As an example, the pulse stretcher may be configured to apply 2nd order dispersion having a value of between 30 ps2to 140 ps2, such as between 60 ps2to 120 ps2, such as between 80 ps2to 110 ps2. In some embodiments, the pulse stretcher is configured to at least partially compensate for 3rd order dispersion. As an example, the pulse stretcher is configured to apply 3rd order dispersion having a value of between -10 ps3to -0.1 ps3, such as between -5 ps3to about -0.3 ps3, such as about -3.5 ps3to about -0.5 ps3. In some embodiments, the pulse stretcher is configured to at least partially compensate for 4th order dispersion. As an example, the pulse stretcher may be configured to apply 4th order dispersion having a value of between 0.01 ps4to 1 ps4, such as between 0.05 ps4to 0.75 ps4, such as between 0.1 ps4to about 0.5 ps4. Thus, the pulse stretcher may be configured to at least partially compensate one or more of 2nd, 3rd, and / or 4th order dispersion of the modified pulses, such as by the values provided as examples herein. The pulse stretcher may have a transmissive bandwidth having a predefined value. In some embodiments, the transmissive bandwidth is selected in the range from about 8 nm to about 24 nm, such as from about 12 nm to about 20 nm, such as from about 14 nm to about 18 nm.

[0033] The pulse stretcher may be arranged upstream of one or more optical amplifiers forming part of the laser pulses. Thus, the pulse stretcher may be configured for providing the stretched laser pulses to said optical amplifier(s).

[0034] The laser system may comprise one or more optical amplifiers for amplifying laser pulses. In particular, the optical amplifier(s) may be configured and arranged to amplify the stretched laser pulses received from the pulse stretcher. Accordingly, the optical amplifier(s) may be arranged downstream of the pulse stretcher, such as between the pulse stretcher and a pulse compressor forming part of the laser system.

[0035] In some embodiments, the optical amplifier(s) comprises or constitutes a regenerative amplifier configured for amplifying the stretched laser pulses, whereby amplified laser pulses are obtained. The regenerative amplifier may comprise a Pockels cell. The regenerative amplifier may further comprise a gain medium, such as a gain crystal for providing a certain gain to the laser pulses. As an example, the gain crystal may be selected from the group of chromium-doped Colquiriite crystals (CrColquiriites), such as CrLiCAF, CrLiSAF, or CrLiSGaF. An advantage hereof is that the wavelength of the pump laser pulses responsible for the optical gain has a better overlap with the wavelength of the stretched laser pulses, whereby a more efficient amplification is achieved. This is in particular the case if the wavelength of the stretched laser pulses is between 760 nm and 790 nm. Thus, the laser system may comprise a CrLiCAF regenerative optical amplifier.

[0036] In some embodiments, the gain medium comprises two or more different materials, such as selected from crystalline and / or amorphous materials. In particular, the gain medium may comprise, or constitute, a bonded gain crystal comprising one or more layers of materials, such as two or more layers of materials, or even three or more layers of materials. The layers may be attached together, such as bonded together. Thus, the gain medium may comprise two or more layers which are bonded together, optionally with an interlayer in between the two layers. The two or more layers may comprise a first layer of a first material and a second layer of a second material. As an example, the first material may be selected from the group of chromium-doped Colquiriite crystals (CrColquiriites), and Alexandrite crystals. The second material may be selected from the group of Sapphire, Yttrium Aluminum Garnet (YAG, Y3AI5O12), Spinel (MgAhO4), Magnesium Oxide (MgO), or other similar materials. In preferred embodiments, the second material is Sapphire.

[0037] In some embodiments, the first and second materials have different thermal properties, such as different thermal conductivities and / or different thermal diffusivities. The combination of the two materials may improve the thermal properties of the gain medium as a whole. In some embodiments, the thermal conductivity of the gain medium is at least 6.5 W / mK, such as at least 9.5 W / mK, such as at least 12.5 W / mK. Furthermore, the first and second layers may have different thicknesses. As an example, the first layer may have a first thickness, wherein the first thickness is between 0.3 mm and 4 mm, such as between 0.4 mm and 3 mm, such as between 0.5 mm and 2 mm. The second layer may have a second thickness, wherein the second thickness is between 0.4 mm and 2.0 mm, such as between 0.6 mm and 1.6 mm, such as between 0.8 mm and 1.2 mm. In some embodiments, at least one of the layer thicknesses, such as the first thickness, increases along a longitudinal direction of the gain medium. In some cases, the second thickness is held constant throughout the gain medium.

[0038] In some embodiments, the gain medium comprises a plurality of pairs of first and second layers, such that the gain medium constitutes a bonded gain crystal having a plurality of layers bonded together. Thus, the gain medium may constitute a bonded gain crystal comprising two or more alternating layers of two different materials. An interlayer may be arranged between the first and second layers in order to improve the bonding of the two materials. In some cases, the interlayer is made of a different material than the first and second layers. In some embodiments, the total length of the gain medium is between 1 mm and 100 mm, such as between 2 mm and 50 mm, such as between 5 mm and 20 mm.

[0039] At least one advantage of the above-described embodiments of a layered gain medium comprising two or more layers of materials, is that the resulting bonded gain crystal has improved thermal and mechanical properties. In general, CrColquiriite based lasers can sometimes suffer from weak thermal and mechanical properties that makes power scaling difficult. Thus, by thermally bonding two different materials to form a layered gain medium, the thermal conductivity and mechanical properties are improved. Consequently, a laser system employing such a gain medium can be scaled to higher optical powers, which is beneficial for many applications such as materials processing and ophthalmology.

[0040] The regenerative amplifier may comprise a regenerative cavity. The regenerative cavity may comprise a plurality of mirrors forming an optical resonator. The regenerative amplifier may further comprise one or more dispersion compensation elements housed inside the cavity or resonator. As an example, one or more of the mirrors may be Gires-Tournois interferometer mirrors for compensating for the group-velocity dispersion of the laser pulses inside the cavity. The aforementioned gain medium may be arranged within the regenerative cavity. The seed pulses, or stretched laser pulses, may undergo multiple passes through the gain medium within the regenerative cavity. Each pass through the gain medium may result in amplification due to stimulated emission. The regenerative cavity may further provide spectral filtering, allowing only the desired wavelength (corresponding to the seed pulses) to resonate within the cavity. After sufficient amplification and spectral narrowing, a fraction of the amplified pulses may be extracted from the cavity. The laser pulses output by the regenerative amplifier may have a higher energy, preferably a much higher energy, and / or a shorter duration compared to the seed laser pulses.

[0041] At least one advantage of utilizing a CrLiCAF crystal over Or: USAF or CrLiSGaF is that thermal lensing occurs at a higher temperature. All three examples of chromium-doped Colquiriite crystals have some issues with thermal lensing. Thus, if the crystal is heated, the crystal undergoes up-conversion and excited state absorption; in other words, the lasing level is partially or entirely depopulated, with the consequence that the provided gain is lowered. Another advantage is that the gain provided by the CrLiCAF crystal is closer to the wavelength of the laser pulses to be amplified; whereas CrLiSAF (775-1042 nm) and CrLiSGaF (777- 977 nm) provide gain at other wavelengths as well or at wider wavelength ranges. The CrLiCAF crystal may have an emission bandwidth in the range of 720 nm to 887 nm.

[0042] Another advantage of utilizing a CrLiCAF crystal over e.g. Ti:Sapphire is that CrLiCAF can be pumped by a laser diode, which is cheaper than optically pumping using a laser, for example a green laser. A disadvantage of Ti:Sapphire is that thermal lensing occurs at relatively low temperatures, causing self-focusing and ultimately destruction of the Ti:Sapphire crystal. This can potentially be dealt with by cooling the Ti:Sapphire to low temperatures using cryogenic cooling. However, such solutions are expensive and not feasible.

[0043] The optical amplifier(s), such as the regenerative amplifier, may be arranged upstream of a pulse compressor for temporally compressing the amplified laser pulses from the amplifier(s). The laser system may comprise a pulse compressor for temporally compressing the amplified laser pulses, whereby compressed pulses are obtained. In particular, the pulse compressor may be arranged downstream of the optical amplifier(s) and configured to receive and compress the amplified laser pulses received from the optical amplifier(s).

[0044] The pulse compressor may be configured for compressing the amplified laser pulses to a pulse duration similar to, or shorter than, the pulse duration of the seed laser pulses. As an example, the compressed pulses may have a pulse duration in the femtosecond range, such as a pulse duration of between 1 fs and 1000 fs, such as between 10 fs and 100 fs, such as between 40 fs and 60 fs. In some embodiments, the pulse duration of the compressed pulses is less than 56 fs, such as between 1 fs and 55 fs. Furthermore, the compressed pulses may have a pulse energy of between 0.5 J and 100 pJ, such as between 1 pJ and 20 pJ, such as between 5 pJ and 10 pJ. The compressed pulses may be provided by the laser system at a pulse repetition rate of between 20 kHz and 1000 kHz, such as between 100 kHz and 500 kHz, such as between 200 kHz and 300 kHz. The average power of the laser pulses output by the laser system may be in the range from about 0.5 W to about 25 W, such as from about 1 W to about 10 W, such as from about 1 W to about 5 W. In some embodiments, the laser system is configured for outputting the compressed pulses at an output pulse repetition rate higher than 25 kHz, such as higher than 100 kHz, such as higher than 200 kHz.

[0045] In some embodiments, the laser system is configured for providing laser pulses having a pulse duration between 40 fs and 60 fs, a pulse energy between 5 pJ and 10 pJ, said pulses provided at a pulse repetition rate of between 200 kHz and 300 kHz. Such laser pulses are particularly suitable for ophthalmology applications. The laser system may be a chirped pulse amplification (CPA) laser system for ophthalmology applications. Other applications include ultrafast spectroscopy, multiphoton microscopy, materials processing, and laser surgery, among others. The laser system may be configured for providing pulsed laser light having a wavelength in the infrared range or in the near-infrared range, such as light having a wavelength in the range from about 700 nm to about 1.4 pm.

[0046] In some embodiments, the laser system is configured for outputting laser pulses having a wavelength in the range from about 700 nm to about 1050 nm, such as from about 700 nm to about 800 nm. In some embodiments, the output laser pulses from the disclosed laser system have a wavelength in the range from about 700 nm to about 765 nm. The detailed description provides a number of examples of how to achieve such wavelengths, e.g. using Er-doped seed laser in combination with a nonlinear crystal for frequency doubling, or by using a CrColquiriite (e.g. CrLiCAF) mode-locked laser having a central wavelength around the desired output wavelength, such that no frequency conversion is needed. These examples are non-limiting and meant as exemplary embodiments of how to achieve the disclosed laser system. Other embodiments can be envisaged without departing from the present disclosure, such as by combining different disclosed embodiments to achieve a specific implementation falling within the present disclosure.

[0047] Detailed description of the drawings

[0048] The laser system is described in further detail in the following exemplary embodiments with reference to the figures.

[0049] Fig. 1 shows a schematic of an embodiment of a laser system according to the present disclosure. In this embodiment, the laser system comprises a short-pulse oscillator (102) for generating ultrashort seed laser pulses (104). The term ‘ultrashort’ may refer to pulse durations in the femtosecond (fs) or picosecond (ps) range. As an example, the short-pulse oscillator (102) may be embodied as an Erbium-doped mode-locked laser; either solid-state based or fiber-based. The laser system further comprises a nonlinear crystal (106) arranged downstream of the short-pulse oscillator (102) to receive the seed laser pulses (104), said nonlinear crystal (106) configured for frequency conversion of the seed laser pulses (104), such as by frequency doubling through second harmonic generation (SHG). The nonlinear crystal (106) may be a periodically poled lithium niobate crystal, a Bismuth Borate (BiBo) crystal, or other nonlinear crystals suitable for frequency doubling of laser light pulses. The frequency doubled laser pulses (108) output by the nonlinear crystal may be provided to a pulse stretcher (110) arranged downstream of said nonlinear crystal. The pulse stretcher (110) may be configured for temporally stretching the frequency doubled laser pulses (108), whereby stretched laser pulses (112) are obtained and output from the pulse stretcher. The laser system may further comprise an optical amplifier (114) configured for amplifying the stretched laser pulses (112) to provide amplified laser pulses (116). Thus, the optical amplifier (114) may be arranged downstream of the pulse stretcher (110) and configured to receive the stretched pulses (112). The laser system may further comprise a pulse compressor (118) configured for temporally compressing the amplified laser pulses (116), whereby compressed pulses are obtained and output by the compressor (118). The compressed pulses may have a pulse duration in the femtosecond range. The laser system may be a chirped pulse amplification (CPA) laser system. One or more components of this embodiment may be combined with other embodiments of this disclosure.

[0050] Fig. 2 shows a schematic of an embodiment of a laser system according to the present disclosure. In this embodiment, the laser system comprises a short-pulse oscillator (202) for generating ultrashort seed laser pulses (204). As an example, the short-pulse oscillator (202) may be embodied as an Erbium-doped mode-locked laser; either solid-state based or fiber- based. The laser system further comprises a nonlinear crystal (206) arranged downstream of the short-pulse oscillator (202) to receive the seed laser pulses (204), said nonlinear crystal (206) configured for frequency conversion of the seed laser pulses (204) by frequency doubling through second harmonic generation (SHG). The nonlinear crystal (206) may be a periodically poled lithium niobate crystal, a Bismuth Borate (BiBo) crystal, or other nonlinear crystals suitable for frequency doubling of laser light pulses. The frequency doubled laser pulses (208) output by the nonlinear crystal may be provided to a chirped fiber-Bragg grating (210) arranged downstream of said nonlinear crystal. The chirped fiber-Bragg grating (210) may be configured for temporally stretching the frequency doubled laser pulses (208), whereby stretched laser pulses (212) are obtained and output from the chirped fiber-Bragg grating. The laser system may further comprise a regenerative amplifier (214) configured for amplifying the stretched laser pulses (212) to provide amplified laser pulses (216). Thus, the regenerative amplifier (214) may be arranged downstream of the chirped fiber-Bragg grating (210) and configured to receive the stretched pulses (212). The laser system may further comprise a pulse compressor (218), such as a pair of diffraction gratings, configured for temporally compressing the amplified laser pulses (216), whereby compressed pulses are obtained and output by the compressor (218). The compressed pulses may have a pulse duration in the femtosecond range. The laser system may be a chirped pulse amplification (CPA) laser system. One or more components of this embodiment may be combined with other embodiments of this disclosure.

[0051] Fig. 3 shows a schematic of an embodiment of a laser system according to the present disclosure. In this embodiment, the laser system comprises a solid-state mode-locked laser (302), wherein the laser comprises a gain medium selected from the group of chromium-doped colquiriite crystals, such as CrLiCAF, CrLiSAF, or CrLiSGaF. These materials may have a broad emission band in the near infrared regime. In this embodiment, the solid-state mode- locked laser comprises a CrLiCAF crystal. The mode-locked laser (302) is configured for generating ultrashort seed laser pulses (304). The seed laser pulses (304) may have a central wavelength between 750 nm and 800 nm, such as between 760 nm and 790 nm, such as between 770 nm and 785 nm. The seed laser pulses (304) may have a pulse duration in the femtosecond range, such as a pulse duration of between 10 fs and 450 fs, such as between 50 fs and 300 fs, or less than 250 fs. The laser system further comprises a chirped fiber-Bragg grating (CFBG) (306) arranged downstream of said solid-state mode-locked laser (302). The CFBG (306) is arranged to receive the seed laser pulses (304) and temporally stretch said laser pulses to increase their pulse duration, whereby stretched laser pulses (308) are obtained and output by the CFBG (306). The laser system further comprises a regenerative amplifier (310) arranged downstream of the CFBG (306) to receive the stretched laser pulses (308) and amplify said laser pulses to provide amplified laser pulses (312). In this embodiment, the regenerative amplifier (310) comprises a gain medium, said gain medium comprising a gain crystal selected from the group of chromium-doped Colquiriite crystals (CrColquiriites). In particular, a chromium-doped lithium calcium aluminum fluoride (CrLiCAF) is useful in case the solid-state mode-locked laser is based on a CrLiCAF laser crystal since the gain spectrum then overlaps with the laser spectrum from the solid-state mode-locked laser (302). The laser system may further comprise a pulse compressor (314), such as a pair of diffraction gratings, configured for temporally compressing the amplified laser pulses (312), whereby compressed pulses are obtained and output by the compressor (314). The compressed pulses may have a pulse duration in the femtosecond range. The laser system may be a chirped pulse amplification (CPA) laser system. One or more components of this embodiment may be combined with other embodiments of this disclosure.

[0052] Fig. 4 shows a schematic of an embodiment of a gain medium (400) in accordance with the present disclosure. The gain medium (400) may form part of an amplifier as disclosed herein, such as a regenerative amplifier. In this embodiment, the gain medium (400) comprises two or more layers (402, 404) attached together, such as bonded together. Specifically, the gain medium comprises a first layer (402) of a first material and a second layer (404) of a second material. As an example, the first material may be selected from the group of chromium-doped Colquiriite crystals (CrColquiriites), and Alexandrite crystals. The second material may be Sapphire or another material with similar thermal properties as Sapphire, preferably a material suitable for bonding to CrColquiriite materials. As an example, the first and second layers (402, 404) may be bonded together, optionally via an interlayer (not shown). The same applies to other layers forming part of the gain medium. In this embodiment, the first layer (402) has a first thickness, and the second layer (404) has a second thickness. Furthermore, the thickness of at least one of the layers (402, 404), here exemplified as the first layer (402), increases in a longitudinal direction in the gain medium (400), preferably in a direction (406, 408) along which a laser beam is propagating during operation of the laser system. Alternatively, the gain medium (400) may comprise two or more sections wherein the thickness of the layers remains the same, but wherein the thickness of e.g. the first layer (402) varies among different sections of the gain medium (400), as exemplified in the drawing. Thereby, the gain medium may comprise a plurality of pairs of first and second layers, such that the gain medium constitutes a bonded gain crystal. Some advantages of such a gain medium are improved thermal and mechanical properties. Ophthalmology applications often require a high pulse energy and a high pulse repetition rate. This is sometimes challenging to achieve in CrColquiriites alone because of a relatively low thermal conductivity and other mechanical properties of the CrColquiriite crystals. The disclosed gain medium having layers of alternating materials addresses this challenge and provides an improvement over existing gain media. The gain medium of this embodiment may form part of any of the laser systems discloses herein, such as by constituting the gain medium of the regenerative amplifier of the laser system.

[0053] Further details of the disclosure

[0054] 1. A laser system comprising:

[0055] - an oscillator, or seed laser, configured for generating seed laser pulses;

[0056] - a nonlinear crystal configured for frequency doubling the seed laser pulses from the oscillator or seed laser, whereby modified laser pulses are obtained;

[0057] - a pulse stretcher configured for temporally stretching the modified laser pulses, whereby stretched laser pulses are obtained;

[0058] - an amplifier, such as a regenerative amplifier, configured for amplifying the stretched laser pulses, whereby amplified laser pulses are obtained; and

[0059] - a compressor for temporally compressing the amplified laser pulses, whereby compressed pulses are obtained.

[0060] 2. The laser system according to item 1, wherein the seed laser pulses have a central wavelength between 1500 nm and 1600 nm, such as between 1520 nm and 1580 nm.

[0061] 3. The laser system according to any of the preceding items, wherein the modified laser pulses have a central wavelength between 700 nm and 800 nm, such as between 750 nm and 800 nm.

[0062] 4. The laser system according to any of the preceding items, wherein the modified laser pulses have a central wavelength between 700 nm and 770 nm.

[0063] 5. The laser system according to any of the preceding items, wherein the oscillator is a mode-locked oscillator or a mode-locked laser.

[0064] 6. The laser system according to any of the preceding items, wherein the oscillator comprises a gain material doped with a rare-Earth element, such as Erbium (Er) or Ytterbium (Yb). 7. The laser system according to any of the preceding items, wherein the oscillator is an Er-doped mode-locked oscillator.

[0065] 8. The laser system according to any of the preceding items, wherein the nonlinear crystal is selected from the group of Periodically Poled Lithium Niobate (PPLN), Bismuth Borate (BiBo), Beta Barium Borate (BBO), Lithium Triborate (LBO), or Potassium Dihydrogen Phosphate (KDP).

[0066] 9. The laser system according to any of the preceding items, wherein the modified laser pulses are generated through second harmonic generation (SHG).

[0067] 10. The laser system according to any of the preceding items, wherein the pulse stretcher is a chirped fiber-Bragg grating (CFBG).

[0068] 11. The laser system according to any of the preceding items, wherein the pulse stretcher, such as the CFBG, is tunable such that 2ndand / or 3rdorder dispersion of the modified pulses can be adjusted.

[0069] 12. The laser system according to any of the preceding items, wherein the pulse stretcher, such as the CFBG, is configured for adjusting 2nd, 3rd, and / or 4thorder dispersion of the modified pulses.

[0070] 13. The laser system according to any of the preceding items, wherein the pulse stretcher is configured to at least partially compensate for 2nd order dispersion.

[0071] 14. The laser system according to any of the preceding items, wherein the pulse stretcher is configured to apply 2nd order dispersion having a value of between 30 ps2to 140 ps2, such as between 60 ps2to 120 ps2, such as between 80 ps2to 110 ps2.

[0072] 15. The laser system according to any of the preceding items, wherein the pulse stretcher is configured to at least partially compensate for 3rd order dispersion.

[0073] 16. The laser system according to any of the preceding items, wherein the pulse stretcher is configured to apply 3rd order dispersion having a value of between -10 ps3to -0.1 ps3, such as between -5 ps3to about -0.3 ps3, such as about -3.5 ps3to about -0.5 ps3. 17. The laser system according to any of the preceding items, wherein the pulse stretcher is configured to at least partially compensate for 4th order dispersion.

[0074] 18. The laser system according to any of the preceding items, wherein the pulse stretcher is configured to apply 4th order dispersion having a value of between 0.01 ps4to 1 ps4, such as between 0.05 ps4to 0.75 ps4, such as between 0.1 ps4to about 0.5 ps4.

[0075] 19. The laser system according to any of the preceding items, wherein the pulse stretcher has a transmissive bandwidth having a value in the range from about 8 nm to about 24 nm, such as from about 12 nm to about 20 nm, such as from about 14 nm to about 18 nm.

[0076] 20. The laser system according to any of the preceding items, wherein the pulse stretcher has a transmissive bandwidth having a value of between 8 nm to 24 nm, such as between 12 nm to 20 nm, such as between 14 nm to 18 nm.

[0077] 21 . The laser system according to any of the preceding items, wherein the amplifier is a regenerative amplifier, such as a diode-pumped CrColquiriite regenerative amplifier.

[0078] 22. The laser system according to any of the preceding items, wherein the regenerative amplifier comprises a gain medium.

[0079] 23. The laser system according to item 22, wherein the gain medium comprises one or more gain crystals selected from the group of chromium-doped Colquiriite crystals (CrColquiriites), Sapphire, and Alexandrite crystals.

[0080] 24. The laser system according to any of the items 22-23, wherein the gain medium comprises two or more different materials, such as crystalline and / or amorphous materials.

[0081] 25. The laser system according to any of the items 22-24, wherein the gain medium comprises, or constitutes, a bonded gain crystal comprising one or more layers of materials. 26. The laser system according to any of the items 22-25, wherein the gain medium comprises, or constitutes, a bonded gain crystal comprising two or more layers of materials.

[0082] 27. The laser system according to any of the items 22-26, wherein the gain medium comprises two or more layers attached together, such as bonded together.

[0083] 28. The laser system according to any of the items 25-27, wherein said layers comprise one or more gain crystals selected from the group of chromium-doped Colquiriite crystals (CrColquiriites), and Alexandrite crystals.

[0084] 29. The laser system according to any of the items 25-28, wherein the gain medium comprises at least a first layer of a first material and a second layer of a second material, wherein the first and second layers are bonded together.

[0085] 30. The laser system according to item 29, wherein the first and second materials have different thermal properties, such as different thermal conductivities and / or different thermal diffusivities.

[0086] 31. The laser system according to any of the items 22-30, wherein the thermal conductivity of the gain medium is at least 6.5 W / mK, such as at least 9.5 W / mK, such as at least 12.5 W / mK.

[0087] 32. The laser system according to any of the items 29-31 , wherein the first material is selected from the group of chromium-doped Colquiriite crystals (CrColquiriites), and Alexandrite crystals.

[0088] 33. The laser system according to any of the items 29-32, wherein the second material is selected from the group of Sapphire, Yttrium Aluminum Garnet (YAG, Y3AI5O12), Spinel (MgAhO4), and Magnesium Oxide (MgO).

[0089] 34. The laser system according to any of the items 29-33, wherein the second material is Sapphire.

[0090] 35. The laser system according to any of the items 29-34, wherein the first material is selected from the group of chromium-doped Colquiriite crystals (CrColquiriites), and wherein the second material is Sapphire. 36. The laser system according to any of the items 29-35, wherein the first layer has a first thickness, and the second layer has a second thickness.

[0091] 37. The laser system according to item 36, wherein the first and second thicknesses are different.

[0092] 38. The laser system according to any of the items 36-37, wherein the first thickness is between 0.3 mm and 4 mm, such as between 0.4 mm and 3 mm, such as between 0.5 mm and 2 mm.

[0093] 39. The laser system according to any of the items 36-38, wherein the second thickness is between 0.4 mm and 2.0 mm, such as between 0.6 mm and 1.6 mm, such as between 0.8 mm and 1.2 mm.

[0094] 40. The laser system according to any of the items 36-39, wherein the first thickness increases along a longitudinal direction of the gain medium and wherein the second thickness is constant.

[0095] 41. The laser system according to any of the items 25-40, wherein the layers, such as the first and second layers, have different layer thicknesses.

[0096] 42. The laser system according to any of the items 25-41 , wherein the layer thicknesses increase along a longitudinal direction of the gain medium.

[0097] 43. The laser system according to any of the items 25-42, wherein the layers, such as the first and second layers, have different thermal properties, such as different thermal diffusivities.

[0098] 44. The laser system according to any of the items 22-43, wherein the thermal conductivity of the gain medium is at least 6.5 W / mK, such as at least 9.5 W / mK, such as at least 12.5 W / mK.

[0099] 45. The laser system according to any of the items 25-44, wherein the thickness of at least one of the layers varies, such as increases, in a longitudinal direction in the gain medium, such as in a direction along which a laser beam is propagating during operation of the laser system. 46. The laser system according to any of the items 25-45, wherein the gain medium comprises a plurality of pairs of first and second layers, such that the gain medium constitutes a bonded gain crystal having a plurality of layers bonded together.

[0100] 47. The laser system according to any of the items 25-46, wherein the gain medium has a total length of between 1 mm and 100 mm, such as between 2 mm and 50 mm, such as between 5 mm and 20 mm.

[0101] 48. The laser system according to any of the items 25-47, wherein each pair further comprises an interlayer arranged between the first and second layers, wherein the interlayer is made of a different material than the first and second layers.

[0102] 49. The laser system according to any of the preceding items, wherein the regenerative amplifier comprises one or more gain crystals selected from the group of chromium- doped Colquiriite crystals (CrColquiriites).

[0103] 50. The laser system according to item 49, wherein the gain crystal is selected from the group of CrLiCAF, CrLiSAF, or CrLiSGaF.

[0104] 51. The laser system according to item 49, wherein the gain crystal is selected from the group of CrLiSrAIFe and CrLiSrGaFe.

[0105] 52. The laser system according to any of the items 22-51 , wherein the gain medium constitutes a bonded gain crystal comprising two or more alternating layers of two different materials.

[0106] 53. The laser system according to item 52, wherein at least one of said materials is selected from the group of CrLiCAF, CrLiSAF, CrLiSrAIFe and CrLiSrGaFe or CrLiSGaF.

[0107] 54. The laser system according to any of the preceding items, wherein the oscillator is a fiber-based oscillator.

[0108] 55. The laser system according to any of the preceding items, wherein the oscillator is a solid-state oscillator. 56. The laser system according to any of the preceding items, wherein the oscillator is configured for generating a train of seed laser pulses at a pulse repetition rate of between 0.1 MHz to 200 MHz, such as between 1 MHz and 100 MHz, such as between 10 MHz and 80 MHz.

[0109] 57. The laser system according to any of the preceding items, wherein the laser system is configured for outputting a train of laser pulses at an output pulse repetition rate of between 25 kHz and 1000 kHz, such as between 100 kHz and 500 kHz, such as between 200 kHz and 300 kHz.

[0110] 58. The laser system according to any of the preceding items, wherein the compressed pulses have a pulse duration in the picosecond or femtosecond range.

[0111] 59. The laser system according to any of the preceding items, wherein the compressed pulses have a pulse duration of between 1 fs and 250 fs, such as between 10 fs and 100 fs, such as between 40 fs and 60 fs.

[0112] 60. The laser system according to any of the preceding items, wherein the compressed pulses have a pulse duration between 1 fs and 55 fs.

[0113] 61. The laser system according to any of the preceding items, wherein the compressed pulses have a pulse energy of between 1 J and 100 pJ, such as between 1 pJ and 20 pJ, such as between 5 pJ and 10 pJ.

[0114] 62. The laser system according to any of the preceding items, wherein the compressed pulses have a pulse energy of more than 10 pJ.

[0115] 63. The laser system according to any of the preceding items, wherein the compressed pulses have a pulse energy of less than 10 pJ.

[0116] 64. The laser system according to any of the preceding items, wherein the laser system is configured for outputting the compressed pulses, wherein the average power of the compressed pulses is between 0.1 W and 20 W, such as between 1 Wand 10 W, such as between 1 W and 5 W.

[0117] 65. The laser system according to any of the preceding items, wherein the regenerative amplifier is configured for being pumped by one or more laser diodes. 66. The laser system according to any of the preceding items, wherein the regenerative amplifier is configured for being pumped by a laser-diode array.

[0118] 67. The laser system according to any of the preceding items, wherein the regenerative amplifier comprises one or more dispersion compensation elements inside an optical resonator of the regenerative amplifier.

[0119] 68. The laser system according to any of the preceding items, wherein the regenerative amplifier comprises a Pockels cell.

[0120] 69. The laser system according to item 68, wherein the Pockels cell is configured to set the output pulse repetition rate of the laser system.

[0121] 70. The laser system according to any of the preceding items, wherein the pulse repetition rate of the seed laser pulses is in the MHz range, and wherein the pulse repetition rate of the compressed laser pulses is in the kHz range.

[0122] 71. The laser system according to any of the preceding items, wherein the laser system is configured for ophthalmology applications.

[0123] 72. The laser system according to any of the preceding items, wherein the laser system is configured for one or more applications selected from the group of: ultrafast spectroscopy, multiphoton microscopy, materials processing, and / or laser surgery.

[0124] 73. A laser system comprising:

[0125] - a seed laser for generating seed laser pulses having a central wavelength of between 650 nm and 850 nm, such as between 700 nm and 800 nm;

[0126] - a pulse stretcher configured for temporally stretching the seed laser pulses, whereby stretched laser pulses are obtained;

[0127] - an amplifier, such as a regenerative amplifier, configured for amplifying the stretched laser pulses, whereby amplified laser pulses are obtained; and

[0128] - a compressor for temporally compressing the amplified laser pulses, whereby compressed pulses are obtained. 74. The laser system according to item 73, wherein the seed laser is a solid-state mode- locked laser.

[0129] 75. The laser system according to any of the items 73-74, wherein the seed laser comprises a chromium-doped Colquiriite crystal, such as CrLiCaAIFe (CrLiCAF).

[0130] 76. The laser system according to any of the items 73-75, wherein the seed laser comprises an Alexandrite crystal (Cr^BeAhOt).

[0131] 77. The laser system according to any of the items 73-76, wherein the pulse stretcher is a chirped fiber-Bragg grating (CFBG).

[0132] 78. The laser system according to any of the items 73-77, wherein the amplifier is a regenerative amplifier, such as a diode-pumped regenerative amplifier.

[0133] 79. The laser system according to any of the items 73-78, wherein the regenerative amplifier comprises a gain medium, said gain medium comprising a gain crystal selected from the group of CrColquiriites or Alexandrite crystals (Cr^BeAhOt).

[0134] 80. The laser system according to any of the items 73-79, wherein the compressed pulses have a pulse duration in the picosecond or femtosecond range.

[0135] 81. The laser system according to any of the preceding items, wherein the laser system is an ultrashort laser system for ophthalmology applications.

[0136] 82. The laser system according to any of the preceding items, wherein the laser system a chirped pulse amplification (CPA) laser system for ophthalmology applications.

[0137] Although some embodiments have been described and shown in detail, the disclosure is not restricted to such details, but may also be embodied in other ways within the scope of the subject matter defined in the following claims. In particular, it is to be understood that other embodiments may be utilized, and structural and functional modifications may be made without departing from the scope of the present disclosure. Furthermore, the skilled person would find it apparent that unless an embodiment is specifically presented only as an alternative, different disclosed embodiments may be combined to achieve a specific implementation and such specific implementation is within the scope of the disclosure.

Claims

Claims1. A laser system comprising:- an Er-doped mode-locked oscillator configured for generating seed laser pulses having a central wavelength;- a nonlinear crystal configured for frequency doubling the seed laser pulses from the oscillator, whereby modified laser pulses are obtained;- a chirped fiber-Bragg grating (CFBG) configured for temporally stretching the modified laser pulses, whereby stretched laser pulses are obtained;- a regenerative amplifier configured for amplifying the stretched laser pulses, whereby amplified laser pulses are obtained, wherein the regenerative amplifier comprises a gain medium, said gain medium comprising one or more gain crystals selected from the group of chromium-doped Colquiriite crystals (CrColquiriites), and Alexandrite crystals; and- a compressor for temporally compressing the amplified laser pulses, whereby compressed pulses are obtained, said compressed pulses having a pulse duration in the picosecond or femtosecond range.

2. The laser system according to claim 1 , wherein the nonlinear crystal is selected from the group of Periodically Poled Lithium Niobate (PPLN), Bismuth Borate (BiBo), Beta Barium Borate (BBO), Lithium Triborate (LBO), or Potassium Dihydrogen Phosphate (KDP).

3. The laser system according to any of the preceding claims, wherein the central wavelength of the seed laser pulses is between 1500 nm and 1600 nm.

4. The laser system according to any of the preceding claims, wherein the modified laser pulses have a central wavelength in the range from about 750 nm to about 800 nm.

5. The laser system according to any of the preceding claims, wherein the modified laser pulses are generated through second harmonic generation (SHG).

6. The laser system according to any of the preceding claims, wherein the CFBG is tunable such that 2ndand / or 3rdorder dispersion of the modified pulses can be adjusted.

7. The laser system according to any of the preceding claims, wherein the CFBG is configured for adjusting 2nd, 3rd, and / or 4thorder dispersion of the modified pulses.

8. The laser system according to any of the preceding claims, wherein the gain crystal is selected from the group of CrLiCAF, CrLiSAF, or CrLiSGaF.

9. The laser system according to any of the claims 1-7, wherein the gain crystal comprises, or constitutes, an Alexandrite crystal (Cr^BeAhO^.

10. The laser system according to any of the preceding claims, wherein the Er-doped mode-locked oscillator is a fiber-based oscillator.

11. The laser system according to any of the preceding claims, wherein the Er-doped mode-locked oscillator is a solid-state oscillator.

12. The laser system according to any of the preceding claims, wherein the Er-doped oscillator is configured for generating a train of seed laser pulses at a pulse repetition rate of between 1 MHz and 100 MHz.

13. The laser system according to any of the preceding claims, wherein the laser system is configured to output the compressed pulses at a pulse repetition rate in the range from about 100 kHz to about 500 kHz, such as between 200 kHz and 300 kHz.

14. The laser system according to any of the preceding claims, wherein the compressed pulses have a pulse duration of between 10 fs and 100 fs, such as between 40 fs and 60 fs.

15. The laser system according to any of the preceding claims, wherein the compressed pulses have a pulse energy of between 1 J and 20 pJ, such as between 5 pJ and 10 pJ.

16. The laser system according to any of the preceding claims, wherein the laser system is configured for outputting the compressed pulses, wherein the average power of the compressed pulses is between 1 W and 10 W, such as between 1 W and 5 W.

17. The laser system according to any of the preceding claims, wherein the regenerative amplifier is configured for being pumped by one or more laser diodes.

18. The laser system according to any of the preceding claims, wherein the regenerative amplifier comprises one or more dispersion compensation elements inside an optical resonator of the regenerative amplifier.

19. The laser system according to any of the preceding claims, wherein the gain medium comprises two or more layers of different materials attached together, such as bonded together, optionally with an interlayer arranged between the layers.

20. The laser system according to claim 19, wherein the two or more layers have different thermal properties, such as different thermal diffusivities.21 . The laser system according to any of the claims 19-20, wherein the thermal conductivity of the gain medium is at least 6.5 W / mK, such as at least 9.5 W / mK, such as at least 12.5 W / mK.

22. The laser system according to any of the claims 27-21 , wherein a thickness of at least one of the layers varies, such as increases, along a longitudinal direction of the gain medium.

23. The laser system according to any of the claims 27-22, wherein the gain medium comprises at least a first layer of a first material and a second layer of a second material.

24. The laser system according to claim 23, wherein the first and second layers are bonded together, optionally with an interlayer arranged between the first and second layers.

25. The laser system according to any of the claims 23-24, wherein the first material is selected from the group of chromium-doped Colquiriite crystals (CrColquiriites), and wherein the second material is Sapphire.

26. The laser system according to any of the preceding claims, wherein the laser system is configured for ophthalmology applications.

27. A laser system comprising:- a mode-locked laser for generating seed laser pulses having a central wavelength, wherein the laser comprises a chromium-doped Colquiriite crystal, such as CrLiCaAIFe (CrLiCAF), or a Cr3+:BeAhO4 (Alexandrite) crystal;- a chirped fiber-Bragg grating (CFBG) configured for temporally stretching the seed laser pulses, whereby stretched laser pulses are obtained;- a regenerative amplifier configured for amplifying the stretched laser pulses, whereby amplified laser pulses are obtained, wherein the regenerative amplifier comprises a gain medium, said gain medium comprising one or more gain crystals selected from the group of CrColquiriites and Alexandrite; and- a compressor for temporally compressing the amplified laser pulses, whereby compressed pulses are obtained, wherein said compressed pulses have a pulse duration in the picosecond or femtosecond range.

28. The laser system according to claim 27, wherein the seed laser pulses have a central wavelength in the range from about 700 nm to about 800 nm.

29. The laser system according to any of the claims 27-28, wherein the mode-locked laser is a solid-state mode-locked laser.

30. The laser system according to any of the claims 27-29, wherein the mode-locked laser comprises a CrLiCaAIFe (CrLiCAF) crystal or a Cr3+:BeAhO4 (Alexandrite) crystal.

31. The laser system according to any of the claims 27-30, wherein the regenerative amplifier comprises a Cr3+:BeAhO4 (Alexandrite) crystal.

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