A femtosecond disk laser generating an eye-safe wavelength

Abstract

The present invention discloses a femtosecond disk laser that generates an eye-safe wavelength band, belonging to the field of femtosecond laser technology. The femtosecond disk laser that generates an eye-safe wavelength band includes a pump source, a disk crystal, a pump cavity, and a resonant cavity. The pump cavity allows the pump light emitted by the pump source to pass through the disk laser crystal multiple times and then excite and generate oscillating laser light. In the resonant cavity, the first branch includes a high-dispersion mirror and an output mirror arranged in sequence along the optical path. The oscillating laser light is transmitted along the first branch to the output mirror and then returns to the disk laser crystal along the original path and is reflected to the second branch. The second branch includes a first concave mirror, a second concave mirror, a Cr mirror, and a Cr mirror arranged in sequence along the optical path. 4+ :YAG crystal and high reflective mirror; Cr 4+ The YAG crystal acts as a passive mode-locking device and also as a gain medium to generate eye-safe femtosecond laser pulse trains. This femtosecond disk laser has a simple structure and can produce stable femtosecond laser output in a specific wavelength band.

Description

Technical Field

[0001] The present invention belongs to the field of disk lasers, and more particularly, relates to a femtosecond disk laser that generates an eye-safe wavelength band. Background Art

[0002] The disk technology is to make the gain medium into a thin sheet structure with a diameter of more than 10mm and a thickness of 100-300μm. At the same time, the disk is welded to a tungsten-copper heat sink or glued to a diamond heat sink with better thermal conductivity. The heat on the disk is efficiently removed by an impact water cooling method, so that the crystal has only a one-dimensional thermal gradient distribution, effectively avoiding problems such as thermal lensing, thermal distortion and nonlinear excitation of the gain medium, and providing a guarantee for the generation of femtosecond lasers with high peak power, high average power and high beam quality.

[0003] At present, high-power eye-safe femtosecond lasers are mainly generated based on bulk crystals and nonlinear frequency conversion. The main methods used include using Cr 4+ :YAG crystals are combined with passive mode-locking mechanisms, femtosecond Raman frequency shifts, and optical parametric oscillators, etc., and these methods can be used to achieve femtosecond laser output in a specific band. However, existing lasers have some problems. For example, the use of bulk crystals is limited by the thermal effects and thermal distortion of the crystals under high-power pumping conditions. The average power of the femtosecond pulses of the constructed all-solid-state femtosecond laser is only in the milliwatt range without subsequent amplification. The low average power will significantly reduce the signal-to-noise ratio of the femtosecond pulse laser. The use of femtosecond Raman frequency shift and optical parametric oscillation technology is limited by self-steepening, stimulated Raman scattering, and nonlinear walk-off, resulting in low femtosecond laser conversion efficiency. Therefore, how to find a method that can directly output high-power femtosecond pulses in the human eye-safe band has become an important issue that needs to be solved. Summary of the Invention

[0004] In response to the defects of the existing technology and the need for improvement, the present invention provides a femtosecond laser that generates a waveband that is safe for the human eye, aiming to solve the problem that the existing laser cannot directly generate a high-power femtosecond laser pulse sequence in the waveband that is safe for the human eye.

[0005] To achieve the above-mentioned object, the present invention provides a femtosecond disk laser that generates an eye-safe wavelength band, characterized in that it comprises: a pump source, a disk laser crystal, a pump cavity and a resonant cavity;

[0006] The pump cavity is arranged on the output light path of the pump source; the disk laser crystal is arranged in the pump cavity; the pump cavity allows the pump laser emitted by the pump source to pass through the disk laser crystal multiple times and then excite the disk laser crystal to generate oscillating laser light;

[0007] The resonant cavity is arranged on one side of the output of the oscillating laser describing the disk laser crystal, and the resonant cavity includes a first branch and a second branch;

[0008] The first branch includes a dispersion mirror group, a hard aperture, and an output mirror arranged in sequence along the optical path; the hard aperture is used to assist in passive mode locking; after the oscillating laser is transmitted along the first branch to the output mirror, a portion of the laser light is output through the output mirror, and the remaining laser light returns to the disk laser crystal along the original path and is reflected to the second branch;

[0009] The second branch includes a first concave mirror, a second concave mirror, a Cr 4+ : YAG crystal and high reflective mirror; the focus of the first concave mirror and the second concave mirror coincide, the Cr 4+ : The YAG crystal is located at the focus, and the distance between the first concave mirror and the second concave mirror is located at the center of the stable region of the resonant cavity;

[0010] The Cr 4+ :YAG crystal is used as a saturable absorber for passive mode locking, and the Cr 4+ :YAG crystal also serves as a gain medium, used to generate a femtosecond laser pulse sequence in the human eye-safe band under the action of the oscillating laser; the femtosecond laser pulse sequence in the human eye-safe band is reflected by the high-reflection mirror, returns to the disk laser crystal along the original path, and enters the first branch again after being reflected by the disk laser crystal, and the output mirror outputs the femtosecond laser pulse sequence in the human eye-safe band.

[0011] Optionally, the disk laser crystal is a Yb:YAG crystal, wherein Yb 3+ The doping concentration is 7%;

[0012] The Cr 4+ Cr:YAG crystal 4+ The doping concentration range is 2%-7%, the Cr 4+ :The length of YAG crystal ranges from 10mm to 30mm;

[0013] The central wavelength of the femtosecond laser pulse sequence in the eye-safe band is 1500 nm.

[0014] Optionally, the Cr 4+ : Both sides of the YAG crystal surface are coated with broadband anti-reflection coating for the 1000nm-1070nm and 1300-1600nm bands, with a transmittance greater than 99.9%.

[0015] Optionally, the light-facing surfaces of the dispersion mirror group, the first concave mirror, the second concave mirror and the high-reflection mirror are coated with broadband high-reflection films for the 1000nm-1070nm band and the 1300-1600nm band, with a reflectivity greater than 99.9%.

[0016] Optionally, the dispersion mirror group includes a first high dispersion mirror and a second high dispersion mirror arranged in sequence along the optical path.

[0017] Optionally, the light-facing surface of the output mirror is coated with a film layer that fully reflects the oscillating laser in the 1000nm-1070nm band and partially transmits the 1300-1600nm band, with a transmittance range of 1% to 20%;

[0018] The light-emitting surface of the output mirror is coated with an anti-reflection film for oscillating lasers in the 1300-1600nm band.

[0019] Optionally, the side of the disk laser crystal facing the resonant cavity is coated with an anti-reflection film for the pump laser and the oscillator laser, and the side facing away from the resonant cavity is coated with a high-reflection film for the pump laser and the oscillator laser.

[0020] Optionally, the surface of the disk laser crystal coated with a high-reflection film is fixed on a water-cooled heat sink.

[0021] Optionally, the femtosecond disk laser further includes a crystal fixture;

[0022] The crystal holder holds the Cr 4+ :YAG crystal, the crystal holder is provided with external circulating cooling water for the Cr 4+ :YAG crystal for heat dissipation.

[0023] Compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0024] 1. The present invention provides a femtosecond disk laser that generates a specific wavelength band. It uses a disk laser crystal that is similar to a one-dimensional thin sheet as a gain medium. Under high-power pumping, it can effectively dissipate heat and minimize the generation of thermal effects. The small amount of heat generated can be efficiently removed through a stroke-type water-cooling structure. Therefore, the disk crystal is more compatible with high-power pumping conditions, thereby being able to output high-power femtosecond lasers, while also having a higher average power in the resonant cavity. A passive saturable absorber (Cr) is used, whose absorption spectrum range includes the central wavelength of the oscillating laser generated by the disk laser crystal. 4+:YAG crystal), which is used for passive mode locking and also serves as a gain medium to generate a femtosecond laser pulse sequence in the target band (eye-safe band) under the action of the oscillating laser; thereby directly generating high-power, eye-safe femtosecond laser pulses, and broadening the application scenarios of femtosecond disk lasers.

[0025] 2. The present invention provides a femtosecond disk laser that generates a specific wavelength band, using a Yb:YAG disk as a gain medium. The disk is a thin disk with a thickness of 130 μm and a diameter of 10 mm. Cr 4+ :YAG crystal serves as a passive mode-locked device and also as a gain medium for generating eye-safe lasers, directly outputting high-power eye-safe femtosecond lasers in the resonant cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention provides a schematic structural diagram of a femtosecond disk laser that generates a specific wavelength band;

[0027] The reference numerals in the accompanying drawings are as follows:

[0028] 1. Pump source, 2. Disk laser crystal, 3. Pump cavity, 4. Resonant cavity, 5. Cr 4+ :YAG crystal, 6. First high dispersion mirror, 7. Second high dispersion mirror, 8. Hard aperture, 9. Output mirror, 10. First concave mirror, 11. Second concave mirror, 12. High reflection mirror. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0030] The contents involved in the above embodiment are described below in conjunction with a preferred embodiment.

[0031] like Figure 1 As shown, a femtosecond disk laser generating an eye-safe wavelength band includes: a pump source 1, a disk laser crystal 2, a pump cavity 3, and a resonant cavity 4;

[0032] The pump cavity 3 is arranged on the output light path of the pump source 1; the disk laser crystal 2 is arranged in the pump cavity 3; the pump cavity 3 allows the pump laser emitted by the pump source 1 to pass through the disk laser crystal 2 multiple times and then excite the disk laser crystal 2 to generate oscillating laser light;

[0033] The resonant cavity 4 is arranged on one side of the output of the oscillating laser describing the disk laser crystal, and the resonant cavity 4 includes a first branch and a second branch;

[0034] The first branch includes a dispersion mirror group, a hard aperture 8, and an output mirror 9 arranged in sequence along the optical path; the hard aperture 8 is used to assist in passive mode locking; after the oscillating laser is transmitted along the first branch to the output mirror 9, a portion of the laser light is output through the output mirror 9, and the remaining laser light returns to the disk laser crystal 2 along the original path and is reflected to the second branch;

[0035] The second branch includes a first concave mirror 10, a second concave mirror 11, a Cr 4+ : YAG crystal 5 and high reflective mirror 12; the focus of the first concave mirror 11 and the second concave mirror 11 coincide, the Cr 4+ : The YAG crystal 5 is located at the focus, and the distance between the first concave mirror 10 and the second concave mirror 11 is located at the center of the stable region of the resonant cavity;

[0036] The Cr 4+ :YAG crystal 5 is used as a saturable absorber for passive mode locking, the Cr 4+ :YAG crystal also serves as a gain medium, used to generate a femtosecond laser pulse sequence in the human eye-safe band under the action of the oscillating laser; the femtosecond laser pulse sequence in the human eye-safe band is reflected by the high-reflection mirror 12, returns along the original path to the disk laser crystal 2, and enters the first branch again after being reflected by the disk laser crystal 2, and the output mirror 9 outputs the femtosecond laser pulse sequence in the human eye-safe band.

[0037] The central wavelength of the oscillation laser generated by the disk laser crystal 2 is 4+ : Within the absorption spectrum of YAG crystal 5, the oscillating laser is used as the Cr 4+ :YAG crystal 5 pump light source enables it to produce femtosecond laser pulse sequences in the human eye-safe band.

[0038] In order to make the disk laser produce stable and sustainable femtosecond pulse output without increasing the structural complexity and energy loss, the present invention provides a femtosecond disk laser that produces a human eye-safe band, using Cr 4+ :YAG crystal 5 is used as a saturable absorber for passive mode locking in the 1030nm band. At the same time, since the central wavelength of the oscillating laser generated by the disk laser crystal 2 is in the selected Cr 4+ :YAG crystal 5 fluorescence absorption spectrum range, therefore, Cr 4+The YAG crystal 5 also serves as a gain medium, generating eye-safe femtosecond laser pulse trains from the oscillating laser light generated by the disk laser crystal 2. The femtosecond laser pulse trains output by this femtosecond disk laser have femtosecond-scale widths, and the high power and stability of the femtosecond laser pulses significantly simplify the design and operation of the device.

[0039] The disk laser crystal 2 serves as a gain medium, absorbing the energy from the pump laser to generate oscillating laser light. It also acts as a reflective mirror within the resonant cavity, reflecting the oscillating laser light. Therefore, different dielectric coatings are applied to both sides of the disk laser crystal 2: an anti-reflection coating for the pump and oscillating laser light on the side facing the resonant cavity, and a high-reflection coating for both the pump and oscillating laser light on the side facing away from the resonant cavity. The surface of the disk laser crystal 2 coated with the high-reflection coating is fixed to a water-cooled heat sink with a stroke structure.

[0040] Optionally, according to the mode distribution in the cavity, hard apertures 8 of different sizes are set at different positions in the cavity to increase the diffraction loss in the cavity to assist in mode locking.

[0041] like Figure 1 As shown, the pump source 1 is used to generate pump laser light. Semiconductor lasers, fiber lasers, and solid-state lasers can be used. In this embodiment, a semiconductor laser with fiber-coupled output is used as the pump source, and the pump laser wavelength is 940 nm or 969 nm. In this embodiment, the pump cavity 3 includes a parabolic mirror and a series of refraction prisms. These mirrors are positioned in the optical path between the pump source 1 and the disk laser crystal 2 according to a predetermined pattern. The disk laser crystal 2 is placed at the focus of the parabolic mirror. The input pump light is focused onto the disk laser crystal 2 after multiple reflections from the parabolic mirror and the refraction prisms. The disk laser crystal 2 is a disc-shaped Yb:YAG (doping concentration 7%) laser crystal with a diameter of 10 mm and a thickness of 130 μm. Made of the well-established Yb:YAG material, it provides the gain medium for 1030 nm laser generation and is located within the pump cavity 3. The pump cavity 3 allows the pump laser emitted by the pump source 1 to pass through the disk laser crystal 2 multiple times and then excite the disk laser crystal 2 to generate oscillating laser light.

[0042] Furthermore, this embodiment employs a 48-pass pumping structure, meaning the pump laser passes through the disk laser crystal 2 48 times, significantly improving the disk crystal's absorption efficiency of the pump light. In other embodiments, a 24-pass pumping structure, a 36-pass pumping structure, or even a 72-pass pumping structure may be employed, depending on actual needs.

[0043] In this embodiment, the resonant cavity 4 is used to output femtosecond pulses in a wide wavelength band of 1300-1600 nm. It is located on one side of the oscillating laser output from the disk laser crystal and includes a first branch and a second branch.

[0044] In this embodiment, the dispersion mirror specifically includes a first high-dispersion mirror 6 and a second high-dispersion mirror 7 arranged in sequence along the optical path; after the oscillating laser is incident on the first branch from the disk laser crystal 2, it first enters the first high-dispersion mirror 6, and then is reflected on the second high-dispersion mirror 7, and then is reflected on the output mirror 9. Part of the laser light is output through the output mirror 9, and the remaining laser light is reflected by the output mirror 6, returns to the disk laser crystal 2 along the original path, and is reflected to the second branch.

[0045] In this femtosecond disk laser, Cr 4+ :YAG crystal 5 is used as a modulator for passive mode locking in the 1030nm band. 4+ :YAG crystal 5 has a strong fluorescence absorption spectrum in the range of 970nm-1100nm; therefore, the 1030nm femtosecond laser in the resonant cavity can be used as Cr 4+ : Pump light source generated by YAG crystal femtosecond laser in the human eye-safe band.

[0046] The disk laser crystal 2 of the femtosecond disk laser is a Yb:YAG crystal, which produces an oscillating laser with a central wavelength of 1030nm. The oscillating laser oscillates back and forth between the first branch, the disk laser crystal and the second branch, and is continuously irradiated by Cr 4+ :YAG crystal is modulated to form a high-power stable femtosecond laser pulse sequence with a central wavelength of 1030nm.

[0047] Furthermore, Cr 4+ :YAG crystal 5 continuously absorbs the 1030nm band femtosecond laser in the resonant cavity. When the gain of the 1300-1600nm band laser is greater than the loss, a broadband human eye-safe band femtosecond laser will be generated in the resonant cavity. It is continuously amplified by the reflector in the resonant cavity to form a stable pulse sequence, and part of it is output through the output mirror 6. The remaining part returns to the disk laser crystal 2 along the original path and is reflected to the second branch, realizing the round-trip oscillation of the oscillating laser in the resonant cavity.

[0048] Furthermore, Cr 4+ : The length of YAG crystal 5 is selected in the range of 10mm-30mm, Cr 4+ The doping concentration of the ions can be selected within the range of 2%-7%, that is, different crystal lengths and doping concentrations can be combined with each other and adjusted accordingly according to experimental phenomena.

[0049] In order to further reduce the energy loss in the resonant cavity, the Cr 4+ : The light-transmitting surface of the YAG crystal 5 is optimized. Specifically, the Cr 4+: Both sides of the YAG crystal surface are coated with broadband anti-reflection coating for the 1000nm-1070nm and 1300-1600nm bands, with a transmittance greater than 99.9%.

[0050] Optionally, the light-facing surfaces of the dispersion mirror group, the first concave mirror 10, the second concave mirror 11 and the high-reflection mirror 12 are coated with broadband high-reflection films for the 1000nm-1070nm band and the 1300-1600nm band, with a reflectivity greater than 99.9%.

[0051] Optionally, the light-facing surface of the output mirror 9 is coated with a film layer that fully reflects the oscillating laser in the 1000nm-1070nm band and partially transmits the 1300-1600nm band, with a transmittance range of 1% to 20%;

[0052] The light-emitting surface of the output mirror 9 is coated with an anti-reflection film for oscillating lasers in the 1300-1600 nm band.

[0053] The reflective surface of the output mirror 9 is also coated with a high-reflective film for 1000nm-1070nm and oscillating lasers, with a reflectivity greater than 99.9%.

[0054] The front surfaces of the first concave mirror 10, the second concave mirror 11 and the high-reflection mirror 12 in the resonant cavity 4 are coated with a 1300-1600nm high-reflection film, and the front surface of the output mirror 9 is coated with a 1300-1600nm partially transmissive film, thereby ensuring that the 1300-1600nm femtosecond laser oscillates and strengthens back and forth between the first branch, the disk laser crystal and the second branch, and ultimately outputs high-power femtosecond laser pulses in the human eye-safe band.

[0055] Optionally, the femtosecond disk laser further includes a crystal fixture;

[0056] The crystal holder holds the Cr 4+ : YAG crystal 5, the crystal holder is provided with external circulating cooling water for the Cr 4+ :YAG crystal 5 for heat dissipation.

[0057] Furthermore, Cr 4+ : The YAG crystal 5 is wrapped with silver foil and clamped by a crystal fixture. The crystal fixture is made of copper. The crystal fixture has external circulating cooling water and adjusts the temperature according to the average power in the resonant cavity. The wrapped silver foil is used for Cr 4+ :YAG crystal 5 and copper material fit more closely, improving the cooling effect.

[0058] Using the above-mentioned femtosecond disk laser, Cr 4+The YAG crystal serves as both a component for passive mode locking in the 1μm band and a gain medium for eye-safe femtosecond laser generation, enabling stable, high-power femtosecond laser pulses in the eye-safe band (target band), significantly simplifying device design and operation. The femtosecond disc laser generating a specific wavelength, provided by the present invention, has a simple and compact structure and is widely applicable in fields such as lidar, industrial ranging, and ophthalmic surgery, with promising development and application prospects.

[0059] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A femtosecond disk laser generating an eye-safe wavelength band, characterized in that: include: Pump source (1), disk laser crystal (2), pump cavity (3) and resonant cavity (4); The pump cavity (3) is arranged on the output light path of the pump source (1); the disk laser crystal (2) is arranged in the pump cavity (3); the pump cavity (3) allows the pump laser emitted by the pump source (1) to pass through the disk laser crystal (2) multiple times and then excite the disk laser crystal (2) to generate oscillating laser light; The resonant cavity (4) is arranged on one side of the output of the oscillating laser describing the disk laser crystal, and the resonant cavity (4) comprises a first branch and a second branch; The first branch includes a dispersion mirror group, a hard aperture (8), and an output mirror (9) arranged in sequence along the optical path; the hard aperture (8) is used to assist passive mode locking; after the oscillating laser is transmitted along the first branch to the output mirror (9), a portion of the laser is output through the output mirror (9), and the remaining laser returns to the disk laser crystal (2) along the original path and is reflected to the second branch; The second branch comprises a first concave mirror (10), a second concave mirror (11), a Cr 4+ : YAG crystal (5) and high reflective mirror (12); the focus of the first concave mirror (11) and the second concave mirror (11) coincide, the Cr 4+ : the YAG crystal (5) is located at the focus, and the distance between the first concave mirror (10) and the second concave mirror (11) is located at the center of the stable region of the resonant cavity; The Cr 4+ :YAG crystal (5) as a saturable absorber for passive mode locking, the Cr 4+ The YAG crystal also serves as a gain medium for generating a femtosecond laser pulse sequence in the human eye-safe band under the action of the oscillating laser; the femtosecond laser pulse sequence in the human eye-safe band is reflected by the high-reflection mirror (12), returns to the disk laser crystal (2) along the original path, and enters the first branch again after being reflected by the disk laser crystal (2), and the output mirror (9) outputs the femtosecond laser pulse sequence in the human eye-safe band.

2. The femtosecond disk laser according to claim 1, wherein: The disk laser crystal (2) is a Yb:YAG crystal, wherein Yb 3+ The doping concentration is 7%; The Cr 4+ :Cr of YAG crystal (5) 4+ The doping concentration range is 2%-7%, the Cr 4+ : The length of the YAG crystal (5) ranges from 10 mm to 30 mm; The central wavelength of the femtosecond laser pulse sequence in the eye-safe band is 1500 nm.

3. The femtosecond disk laser according to claim 2, wherein: The Cr 4+ : Both sides of the surface of the YAG crystal (5) are coated with broadband anti-reflection films for the 1000nm-1070nm and 1300-1600nm bands, with a transmittance greater than 99.9%.

4. The femtosecond disk laser according to claim 2, wherein: The light-facing surfaces of the dispersion mirror group, the first concave mirror (10), the second concave mirror (11) and the high-reflection mirror (12) are coated with broadband high-reflection films for the 1000nm-1070nm band and the 1300-1600nm band, with a reflectivity greater than 99.9%.

5. The femtosecond disk laser according to claim 4, wherein: The dispersion mirror group comprises a first high dispersion mirror (6) and a second high dispersion mirror (7) which are sequentially arranged along the optical path.

6. The femtosecond disk laser according to claim 2, wherein: The light-facing surface of the output mirror (9) is coated with a film layer that fully reflects the oscillating laser in the 1000nm-1070nm band and a film layer that partially transmits the 1300-1600nm band, with a transmittance range of 1% to 20%; The light-emitting surface of the output mirror (9) is coated with an anti-reflection film for oscillating laser light in the 1300-1600 nm band.

7. The femtosecond disk laser according to any one of claims 1 to 6, wherein: The side of the disk laser crystal (2) facing the resonant cavity (4) is coated with an anti-reflection film for pump laser and oscillating laser, and the side facing away from the resonant cavity (4) is coated with a high-reflection film for pump laser and oscillating laser.

8. The femtosecond disk laser according to claim 7, wherein: The surface of the disk laser crystal (2) coated with a high-reflection film is fixed on a water-cooled heat sink.

9. The femtosecond disk laser according to claim 1, wherein: The femtosecond disk laser further includes a crystal holder; The crystal holder holds the Cr 4+ :YAG crystal, the crystal holder is provided with external circulating cooling water for the Cr 4+ :YAG crystal for heat dissipation.

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