Water-cooling femtosecond laser regenerative amplification device and amplification method thereof

Abstract

The invention provides a water-cooling femtosecond laser regenerative amplification device and an amplification method thereof. The two laser crystals are used, specific laser crystal materials are selected, heat loads on the laser crystals can be reduced, and the problem that the laser is unstable due to heat distribution changes in the laser crystals caused by pump laser energy changes is solved by designing the resonant cavity; the laser crystal only needs to be cooled by a water cooling machine; and more convenient laser import and export are obtained by using the double Pockels cells.

Description

Technical Field

[0001] This invention belongs to the field of femtosecond lasers, specifically relating to a water-cooled femtosecond laser regeneration amplification device and its amplification method. Background Technology

[0002] In current technologies, Ti:Sapphire regenerative amplifiers consist of a Ti:Sapphire crystal, a Pockels cell, a Glan prism for laser input and output, and two end mirrors for laser oscillation. Other mirrors are primarily used for optical path folding to reduce size. However, this approach is only suitable for low power and low pulse repetition frequency operation. If the pump power is high and the pulse repetition frequency exceeds 1kHz, the heat generated by the laser pulse gradually accumulates in the crystal, easily leading to laser parameter deterioration or even crystal damage. Therefore, high repetition rate regenerative amplifiers require cooling the Ti:Sapphire laser crystal at even lower temperatures to remove heat accumulation. This is typically achieved by placing the Ti:Sapphire crystal in a vacuum cavity and using liquid nitrogen or similar coolants to conduct the low temperature to the laser crystal and remove the heat.

[0003] However, the above solutions only allow the laser to operate at low power and low pulse repetition frequency, or require auxiliary structures and consumables such as vacuum cavities and cryogenic refrigerants, increasing technical difficulty and cost. When the pump laser power changes, the laser crystal acts as a changing lens, causing the output laser to be unstable. Using only a single Pockel cell and polarization element in the laser results in lower cost, but the simultaneous input and output pulses place high demands on the falling edge accuracy of the drive circuit. Summary of the Invention

[0004] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a water-cooled femtosecond laser regeneration amplification device and its amplification method. This invention uses two Ti:sapphire laser crystals to distribute the pump laser energy across the two crystals, reducing the impact of thermal effects on a single laser crystal. By designing the laser resonant cavity, the instability of the laser caused by changes in the thermal lens within the crystal is compensated for. Two Pockels cells and two polarization optical elements are used for laser input and output, respectively, making pulse input and output more flexible.

[0005] Before describing the content of this invention, the following terms are defined as follows:

[0006] The term "S-polarized laser" refers to a laser whose reflection and transmission characteristics depend on polarization when light passes through the surface of an optical element (such as a beam splitter) at a non-perpendicular angle. In this case, the coordinate system used is defined by the plane containing the input and reflected beams. If the polarization vector is perpendicular to this plane, it is called an S-polarized laser.

[0007] The term "P-polarized laser" refers to a laser whose reflection and transmission characteristics depend on polarization when light passes through the surface of an optical element (such as a beam splitter) at a non-perpendicular angle. In this case, the coordinate system used is defined by the plane containing the input and reflected beams. If the polarization vector of the light lies in this plane, it is called a P-polarized laser.

[0008] The term "Pockels cell" refers to a fast optical switching device based on the electro-optic effect.

[0009] To achieve the above objectives, a first aspect of the present invention provides a water-cooled femtosecond laser regeneration and amplification device, the water-cooled femtosecond laser regeneration and amplification device comprising: a resonant cavity, a laser crystal, a pump optical path, a laser input / output assembly, and a synchronization circuit;

[0010] The laser crystal is made of two pieces, and its material is either titanium-doped sapphire laser crystal or yttrium aluminum garnet-doped crystal, with titanium-doped sapphire laser crystal being the most preferred.

[0011] According to a first aspect of the present invention, a water-cooled femtosecond laser regeneration and amplification apparatus, wherein the resonant cavity comprises: an end mirror, a concave mirror, and a dual-color planar pump mirror; wherein,

[0012] The number of end mirrors is 2;

[0013] The number of concave mirrors is 0 to 3, preferably 1 to 3, more preferably 2 to 3, and most preferably 3; and / or

[0014] The number of the two-color planar pump mirrors is 0 to 2, preferably 0 or 2;

[0015] Preferably, when the number of the two-color planar pump mirrors is 0, a red light focusing lens is used instead of the one concave mirror;

[0016] More preferably, the optional, unalternative concave mirror is a bicolor concave pump mirror; and / or

[0017] More preferably, the number of red light focusing lenses is 1 to 3, and most preferably 1.

[0018] According to the water-cooled femtosecond laser regeneration and amplification apparatus of the first aspect of the present invention, wherein...

[0019] The end mirror is selected from one or more of the following: plane mirror, concave mirror, convex mirror, preferably plane mirror and / or concave mirror, and most preferably 0-degree plane mirror;

[0020] The bandwidth of the film layer of the end mirror is 750nm to 1150nm, preferably 750nm to 1000nm, and more preferably 750nm to 850nm;

[0021] The concave mirror is a concave reflecting mirror, and the concave reflecting mirror is preferably a 0-degree concave reflecting mirror;

[0022] The concave mirror has a film bandwidth of 750nm to 1150nm, preferably 750nm to 1000nm, and more preferably 750nm to 850nm.

[0023] The curvature of the concave mirror is 150–1000 mm, preferably 200–800 mm, more preferably 250 mm and / or 500 mm; and / or

[0024] The dual-color planar pump mirror is a dual-color planar pump mirror with double-sided coating.

[0025] According to a water-cooled femtosecond laser regeneration and amplification apparatus of a first aspect of the present invention, the intracavity coating of the dual-color planar pump mirror includes a 0-degree reflective coating and a 0-degree transmissive coating, and the external coating of the dual-color planar pump mirror is a 0-degree transmissive coating; wherein...

[0026] The 0-degree reflective film has a bandwidth of 750nm to 1150nm, preferably 750nm to 1000nm, and more preferably 750nm to 850nm; and / or

[0027] The bandwidth of the 0-degree transmission film is 500nm to 550nm, preferably 505nm to 540nm, and more preferably 515nm to 532nm.

[0028] According to a first aspect of the present invention, a water-cooled femtosecond laser regeneration and amplification apparatus is provided, wherein the pump optical path comprises: a pump laser and a green light focusing lens; wherein,

[0029] The number of green light focusing lenses is 2 to 6, preferably 2 to 4, and most preferably 2;

[0030] Preferably, the pump optical path further includes: a green light guide mirror and / or a green light beam splitter;

[0031] More preferably, the number of green light guide mirrors is 1 to 10, more preferably 2 to 4, and most preferably 2; and / or

[0032] More preferably, the number of green beam splitters is one.

[0033] According to the water-cooled femtosecond laser regeneration and amplification apparatus of the first aspect of the present invention, wherein...

[0034] The pump laser is a green laser or a blue laser, with a green laser being the most preferred.

[0035] The wavelength of the pump laser is 500nm to 550nm, preferably 505nm to 540nm, and more preferably 515nm to 532nm;

[0036] The green light guide mirror is a coated optical lens, and the reflectivity of the coated optical lens to the pump laser is 99% to 100%, preferably 99.5% to 100%, and more preferably 99.9% to 100%.

[0037] The green beam splitter is an optical lens, and the transmission-reflection beam splitting ratio of the pump laser by the optical lens is 40% to 60%, preferably 45% to 55%, and most preferably 50%; and / or

[0038] The green light focusing lens is a coated optical lens, and the transmittance of the coated optical lens to the pump laser is 99% to 100%, preferably 99.5% to 100%, and more preferably 99.9% to 100%.

[0039] According to a first aspect of the present invention, a water-cooled femtosecond laser regeneration and amplification apparatus is provided, wherein the laser import / export assembly comprises: a thin-film polarizer and a Pockels cell; wherein,

[0040] The number of the thin-film polarizers is 2 to 4, preferably 2 to 3, and most preferably 2; and / or

[0041] The number of Pockels is 1 to 2, with 2 being the most preferred.

[0042] According to the water-cooled femtosecond laser regeneration and amplification apparatus of the first aspect of the present invention, wherein...

[0043] The thin-film polarizer is an optical polarizer that reflects S-polarized laser light and transmits P-polarized laser light; and / or

[0044] The Pockel cell is an electro-optic switch containing an electro-optic crystal, which generates a 1 / 4 waveplate phase delay on the laser crystal when a voltage is applied.

[0045] According to a water-cooled femtosecond laser regeneration amplification apparatus of the first aspect of the present invention, the synchronization circuit is used to provide a time synchronization circuit signal for the operation of the water-cooled femtosecond laser regeneration amplification apparatus, preferably an electronic synchronization delay device;

[0046] Preferably, the synchronization circuit divides the input oscillator laser pulse radio frequency signal into at least three output channels, and can independently tune the delay and gate width of the output electronic signal of each channel.

[0047] A second aspect of the present invention provides a method for amplifying a femtosecond laser, the method using the water-cooled femtosecond laser regeneration amplification device described in the first aspect to amplify the femtosecond laser;

[0048] Preferably, the method includes:

[0049] When the water-cooled femtosecond laser regeneration amplification device is in the off state, the water-cooled femtosecond laser regeneration amplification device does not generate laser light;

[0050] When the water-cooled femtosecond laser regeneration amplification device is in a spontaneous oscillation state, laser oscillation is generated in the resonant cavity;

[0051] When the water-cooled femtosecond laser regeneration amplification device is in laser amplification mode, the ultrafast laser injected into the water-cooled femtosecond laser regeneration amplification device is amplified and extracted.

[0052] According to a preferred embodiment of the present invention, such as Figure 1 As shown, the water-cooled femtosecond laser regeneration and amplification device of the present invention comprises a resonant cavity, a laser crystal, a pump optical path, a laser import / export component, and a synchronization circuit.

[0053] The resonant cavity is composed of 1-first end mirror, 2-first concave mirror, 3-first bicolor plane pump mirror, 4-second concave mirror, 5-second bicolor plane pump mirror, 6-third concave mirror, and 7-second end mirror.

[0054] The laser crystal consists of two pieces: 8 - the first titanium-doped sapphire crystal and 9 - the second titanium-doped sapphire crystal.

[0055] The pump light path passes through the pump laser via 10-pump laser, 11-first green light guide mirror, 12-green light beam splitter, 13-second green light guide mirror, 14-first green light focusing lens, and 15-second green light focusing lens, and is focused into the titanium-doped sapphire crystal through the two-color plane pump mirror.

[0056] The laser import and export assembly consists of 16-first thin-film polarizer, 17-second thin-film polarizer, 18-first Pockel cell, and 19-second Pockel cell;

[0057] The synchronization circuit is a 20-electronic synchronous delay unit, which provides a time synchronization circuit signal for the operation of the laser.

[0058] The selected components are as follows:

[0059] The first and second end mirrors are 0-degree plane mirrors coated with high-reflection films, and the film bandwidth should cover at least 750nm to 850nm.

[0060] The first and third concave mirrors are 0-degree concave mirrors coated with high-reflectivity films. The bandwidth of the film should cover at least 750nm to 850nm, and the curvature is related to the cavity stabilization parameters and can be 500mm.

[0061] The second concave mirror is a 0-degree concave mirror coated with a high-reflection film. The bandwidth of the film should cover at least 750nm to 850nm, and the curvature is related to the cavity stabilization parameters and can be 250mm.

[0062] The first and second bicolor planar pump mirrors are coated on both sides. The film layer inside the cavity includes a 0-degree high-reflectivity film and a 0-degree high-transmission film. The high-reflectivity film should cover a bandwidth of at least 750nm to 850nm, and the high-transmission film can cover a bandwidth of 515nm to 532nm depending on the pump source wavelength. The coating outside the cavity is a 0-degree high-transmission film, which can cover a bandwidth of 515nm to 532nm depending on the pump source wavelength.

[0063] The first and second titanium-doped sapphire crystals are titanium-doped sapphire laser crystals with a certain doping concentration.

[0064] The pump laser can be a green laser between 515nm and 532nm, with a repetition frequency of over kHz.

[0065] The first and second green light guide mirrors are coated optical lenses with high reflectivity to the pump source laser.

[0066] The green beam splitter is an optical lens that has a certain transmission-reflection beam splitting ratio for the pump source laser;

[0067] The first and second green light focusing lenses are coated optical lenses with high transmittance to the pump source laser.

[0068] The first and second thin-film polarizers are optical polarizers that have high reflectivity to S-polarized lasers and high transmittance to P-polarized lasers.

[0069] The first and second Pockels are electro-optic switches based on electro-optic crystals, which can operate at high repetition rates and produce a phase delay equivalent to a quarter-wave plate for Ti:sapphire lasers when voltage is applied.

[0070] The electronic synchronous delay unit should be able to divide the input oscillator laser pulse radio frequency signal into at least 3 output channels, and independently tune the delay and gate width of the output electronic signal of each channel.

[0071] The operating states of a laser include cutoff state, spontaneous oscillation state, and laser amplification state.

[0072] When the laser is operating in the cutoff state, it does not produce laser light regardless of whether pump light or seed laser light is incident on the laser crystal. At this time, neither the first nor the second Pockel cell is driven by a high-voltage electrical signal. The first Pockel cell is pre-adjusted to the optical 1 / 4 waveplate operating state, and the second Pockel cell is pre-adjusted to the optical 0 waveplate operating state. When spontaneous emission light passes back and forth through the first Pockel cell, it is equivalent to a 1 / 2 waveplate, resulting in polarization rotation. S-polarized light will experience significant losses when passing through the polarization selection element within the cavity, such as a thin-film polarizer, preventing laser oscillation.

[0073] When the laser operates in spontaneous oscillation mode, laser oscillation occurs within the resonant cavity. The pump laser, after being guided and split, passes through a first green focusing lens and a second green focusing lens, respectively, and is incident on two titanium-sapphire crystals to supply energy to the laser crystals. A first Pockel cell periodically applies a quarter-wavelength voltage drive signal, which, when superimposed with a pre-placed optical quarter-wave plate, is equivalent to a half-wave plate. When light passes back and forth through this Pockel cell, it is equivalent to a full-wave plate, and the polarization remains unchanged. P-polarized light within the cavity can pass through all polarization-selective elements with low loss and without polarization rotation, thus generating laser light. If a quarter-wave plate is added between the second thin-film polarizer and the second Pockel cell, or if a quarter-wavelength voltage is applied to the second Pockel cell, a Q-switched laser that amplifies the spontaneous emission can be derived.

[0074] When the laser operates in laser amplification mode, the energy of the ultrafast laser injected into the laser can be amplified and extracted. During the aforementioned spontaneous oscillation state, a low-power S-polarized seed laser is introduced into the resonant cavity from the first thin-film polarizer. It then passes through the first concave mirror, the first laser crystal, the first two-color plane pump mirror, the second concave mirror, the second two-color plane pump mirror, the second laser crystal, and the third concave mirror before reaching the first Pockel cell. By adjusting the synchronization signal of the synchronization circuit, the rising edge signal triggering the Pockel cell is adjusted so that after the seed laser passes through the first Pockel cell twice, it changes from S-polarization to P-polarization after passing through a preset quarter-wave plate. Simultaneously, the first Pockel cell begins operating at a high-voltage quarter-wave plate, effectively acting as a half-wave plate when superimposed with the preset optical quarter-wave plate. Afterward, the polarization of the seed laser no longer changes after passing through the first Pockel cell. The P-polarized seed laser oscillates and amplifies continuously within the resonant cavity until the laser amplification and extraction are complete. The duration of the high voltage in the first Pockel cell is typically from a few microseconds to tens of microseconds. During this period, the energy of the seed laser continuously increases until it saturates. At this point, the high voltage of the second Pockel cell is turned on, so that it operates at a 1 / 4 wave voltage. When the seed amplified laser passes back and forth through the second Pockel cell, its polarization rotates from P polarization to S polarization and is reflected out by the second thin-film polarizer.

[0075] according to Figure 1When the cavity type shown is used, computer simulation results show that when the power of the pump laser changes (i.e., when using...), Figure 3 As shown in the different colors and line curves, the value of the thermal lens changes, causing the spot radius at most locations within the resonant cavity to change. However, the waist spot at the location of the Ti:sapphire laser crystal (within the black vertical dashed line shown in the figure) remains almost unchanged, ensuring relatively stable power during laser amplification.

[0076] Experiments conducted using a laser built according to this cavity design revealed that amplified laser output could be achieved. Water cooling of the crystals was employed, and when two crystals were pumped with a 30W green laser at a repetition rate of 10kHz, a Ti:sapphire laser output of >5W could be achieved without crystal damage, indicating effective thermal management. Using photodiodes and oscilloscopes to detect light leakage in the regenerative amplification device's cavity mirrors allowed for the measurement of the laser's pulse oscillation and lead-out curves. Figure 4 The spectrum and power of the output laser obtained in the experiment are as follows: Figure 5 .

[0077] According to another preferred embodiment of the invention, such as Figure 2 The laser optical path in the image is replaced with a red light focusing lens 21. Figure 1 The second concave mirror 4 in the middle can be omitted. Figure 1 The positions of the first and second bicolor plane pump mirrors in the image, and can be determined by... Figure 2 The first concave mirror 2 and the third concave mirror 6 are replaced with a coated first bicolor concave pump mirror 22 and a coated bicolor concave pump mirror 23. The first green light focusing mirror 14 and the second green light focusing mirror 15 are used to focus the pump laser; they can be collinear with the intracavity laser or at a certain angle to it, thus preventing the laser from passing through the two concave mirrors. The rest are consistent with... Figure 1 Similarly, this scheme can also obtain... Figure 1 Consistent laser output effect.

[0078] This invention uses a resonant cavity with three concave mirrors and two focal points. Two Ti:sapphire laser crystals are placed at the two focal points. Two pump lasers are incident on the Ti:sapphire crystals to provide energy and distribute the heat evenly. The laser crystals only need to be cooled by ordinary water and do not require cryogenic cooling. Two Pockels cells and two polarization elements are used for laser input and output, making beam control more flexible.

[0079] Compared with the prior art, the water-cooled femtosecond laser regeneration amplification device and amplification method of the present invention can have, but are not limited to, the following beneficial effects:

[0080] This invention uses two laser crystals and selects specific laser crystal materials, which can reduce the thermal load on the laser crystals. By designing a resonant cavity, it eliminates the laser instability problem caused by changes in the heat distribution in the laser crystal when the pump laser energy changes. Only a water chiller is needed to cool the laser crystals. The use of dual Pockels cells makes laser import and export more convenient. Attached Figure Description

[0081] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0082] Figure 1 A schematic diagram of the water-cooled femtosecond laser regeneration amplification device of the present invention in Embodiment 1 is shown.

[0083] Figure 2 A schematic diagram of the water-cooled femtosecond laser regeneration amplification device of the present invention in Embodiment 2 is shown.

[0084] Figure 3 The waist spot distribution within the resonant cavity in Example 1 is shown.

[0085] Figure 4 The working state of the water-cooled femtosecond laser regeneration amplification device of the present invention in Embodiment 1 is shown; wherein, Figure 4 A illustrates the water-cooled femtosecond laser regeneration amplification device of the present invention in a spontaneous oscillation operating state; Figure 4 B illustrates the state of the water-cooled femtosecond laser regeneration amplification device of the present invention during laser amplification and output.

[0086] Figure 5 The laser amplification spectrum and output power diagram of the water-cooled femtosecond laser regeneration amplification device of the present invention are shown; wherein, Figure 5 A shows the laser amplification spectrum of the water-cooled femtosecond laser regeneration amplification device of the present invention; Figure 5 B shows a diagram of the laser output power of the water-cooled femtosecond laser regeneration amplification device of the present invention.

[0087] Explanation of reference numerals in the attached figures:

[0088] 1. First end mirror; 2. First concave mirror; 3. First bicolor plane pump mirror; 4. Second concave mirror; 5. Second bicolor plane pump mirror; 6. Third concave mirror; 7. Second end mirror; 8. First titanium-doped sapphire crystal; 9. Second titanium-doped sapphire crystal; 10. Pump laser; 11. First green light guide mirror; 12. Green light beam splitter; 13. Second green light guide mirror; 14. First green light focusing lens; 15. Second green light focusing lens; 16. First thin-film polarizer; 17. Second thin-film polarizer; 18. First Pockel cell; 19. Second Pockel cell; 20. Electronic synchronous delay unit; 21. Red light focusing lens; 22. First bicolor concave pump mirror; 23. Second bicolor concave pump mirror. Detailed Implementation

[0089] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, it should be understood that these embodiments are merely for more detailed and specific explanation and should not be construed as limiting the present invention in any way.

[0090] This section provides a general description of the materials and testing methods used in the experiments of this invention. While many of the materials and methods of operation used to achieve the objectives of this invention are well known in the art, the invention is still described in as much detail as possible herein. It will be apparent to those skilled in the art that, unless otherwise stated in the context, the materials and methods of operation used in this invention are well known in the art.

[0091] Example 1

[0092] This embodiment is an exemplary description of the water-cooled femtosecond laser regeneration amplification device and amplification method of the present invention.

[0093] like Figure 1 As shown, the water-cooled femtosecond laser regeneration and amplification device of the present invention includes: a resonant cavity, a laser crystal, a pump optical path, a laser input / output assembly, and a synchronization circuit. Wherein:

[0094] The resonant cavity includes: a first end mirror 1, a first concave mirror 2, a first bicolor plane pump mirror 3, a second concave mirror 4, a second bicolor plane pump mirror 5, a third concave mirror 6, and a second end mirror 7;

[0095] The laser crystal consists of two pieces: a first titanium-doped sapphire crystal 8 and a second titanium-doped sapphire crystal 9.

[0096] In the pump optical path, the pump laser passes through the pump laser 10, the first green light guide mirror 11, the green light beam splitter 12, the second green light guide mirror 13, the first green light focusing lens 14, and the second green light focusing lens 15, and is focused into the titanium-doped sapphire crystal by the two-color plane pump mirror.

[0097] The laser import and export assembly includes: a first thin-film polarizer 16, a second thin-film polarizer 17, a first Pockel cell 18, and a second Pockel cell 19;

[0098] The synchronization circuit is an electronic synchronization delay unit 20, which provides a time synchronization circuit signal for the operation of the laser.

[0099] The selected components are as follows:

[0100] The first and second end mirrors are 0-degree plane mirrors coated with high-reflection films, and the film bandwidth should cover at least 750nm to 850nm.

[0101] The first and third concave mirrors are 0-degree concave mirrors coated with high-reflectivity films. The bandwidth of the film should cover at least 750nm to 850nm, and the curvature is related to the cavity stabilization parameters and can be 500mm.

[0102] The second concave mirror is a 0-degree concave mirror coated with a high-reflection film. The bandwidth of the film should cover at least 750nm to 850nm, and the curvature is related to the cavity stabilization parameters and can be 250mm.

[0103] The first and second bicolor planar pump mirrors are coated on both sides. The film layer inside the cavity includes a 0-degree high-reflectivity film and a 0-degree high-transmission film. The high-reflectivity film should cover a bandwidth of at least 750nm to 850nm, and the high-transmission film can cover a bandwidth of 515nm to 532nm depending on the pump source wavelength. The coating outside the cavity is a 0-degree high-transmission film, which can cover a bandwidth of 515nm to 532nm depending on the pump source wavelength.

[0104] The pump laser can be a green laser between 515nm and 532nm, with a repetition frequency of over kHz.

[0105] The first and second green light guide mirrors are coated optical lenses with high reflectivity to the pump source laser.

[0106] The green beam splitter is an optical lens that has a certain transmission-reflection beam splitting ratio for the pump source laser;

[0107] The first and second green light focusing lenses are coated optical lenses with high transmittance to the pump source laser.

[0108] The first and second thin-film polarizers are optical polarizers that have high reflectivity to S-polarized lasers and high transmittance to P-polarized lasers.

[0109] The first and second Pockels are electro-optic switches based on electro-optic crystals, which can operate at high repetition rates and produce a phase delay equivalent to a quarter-wave plate for Ti:sapphire lasers when voltage is applied.

[0110] The electronic synchronous delay unit should be able to divide the input oscillator laser pulse radio frequency signal into at least 3 output channels, and independently tune the delay and gate width of the output electronic signal of each channel.

[0111] The operating states of a laser include cutoff state, spontaneous oscillation state, and laser amplification state.

[0112] When the laser is operating in the cutoff state, it does not produce laser light regardless of whether pump light or seed laser light is incident on the laser crystal. At this time, neither the first nor the second Pockel cell is driven by a high-voltage electrical signal. The first Pockel cell is pre-adjusted to the optical 1 / 4 waveplate operating state, and the second Pockel cell is pre-adjusted to the optical 0 waveplate operating state. When spontaneous emission light passes back and forth through the first Pockel cell, it is equivalent to a 1 / 2 waveplate, resulting in polarization rotation. S-polarized light will experience significant losses when passing through the polarization selection element within the cavity, such as a thin-film polarizer, preventing laser oscillation.

[0113] When the laser operates in spontaneous oscillation mode, laser oscillation occurs within the resonant cavity. The pump laser, after being guided and split, passes through a first green focusing lens and a second green focusing lens, respectively, and is incident on two titanium-sapphire crystals to supply energy to the laser crystals. The first Pockel cell is preset to an orientation equivalent to an optical quarter-wave plate. A quarter-wave voltage drive signal is then periodically applied, and the two signals superimposed are equivalent to a half-wave plate. When light passes back and forth through this Pockel cell, it is equivalent to a full-wave plate, and the polarization remains unchanged. P-polarized light within the cavity can pass through all polarization-selective elements with low loss and without polarization rotation, thus generating laser light. If a quarter-wave plate is added between the second thin-film polarizer and the second Pockel cell, or if a quarter-wave voltage is applied to the second Pockel cell, a Q-switched laser that amplifies the spontaneous emission can be derived.

[0114] When the laser operates in laser amplification mode, the energy of the ultrafast laser injected into the laser can be amplified and extracted. During the aforementioned spontaneous oscillation operation, a low-power S-polarized seed laser is introduced into the resonant cavity from the first thin-film polarizer. It then passes through the first concave mirror, the first laser crystal, the first two-color plane pump mirror, the second concave mirror, the second two-color plane pump mirror, the second laser crystal, and the third concave mirror before reaching the first Pockel cell. By adjusting the synchronization signal of the synchronization circuit, the rising edge signal triggering the Pockel cell is adjusted so that after the seed laser passes through the first Pockel cell twice, it changes from S-polarization to P-polarization after two phase delays through a preset equivalent quarter-wave plate. Simultaneously, the first Pockel cell begins operating at a high-voltage quarter-wave plate, superimposed with the preset optical quarter-wave plate to form an equivalent half-wave plate. Afterward, the polarization of the seed laser no longer changes after passing through the first Pockel cell. The P-polarized seed laser continuously oscillates and amplifies within the resonant cavity until the laser amplification and extraction are complete. The duration of the first Pockel cell high voltage is typically from a few microseconds to tens of microseconds. During this period, the energy of the seed laser continuously increases until it saturates. At this point, the second Pockel cell high voltage is activated, operating it at a 1 / 4-wave voltage. When the seed amplified laser passes through the second Pockel cell, the phase delay generated by the 1 / 4-wave voltage causes its polarization to become circularly polarized. After reaching the first end mirror, the seed amplified laser is reflected and returns along the same path, reaching the second Pockel cell again. The phase delay corresponding to another 1 / 4-wave voltage is added, causing it to change from circularly polarized to linearly polarized. At this point, the cumulative phase delay for the P-polarized light is equivalent to a 1 / 2-wave voltage, resulting in polarization rotation from P-polarization to S-polarization. The polarized seed amplified laser is then reflected and extracted by the second thin-film polarizer.

[0115] according to Figure 1 When the cavity type shown is used, computer simulation results show that when the power of the pump laser changes (i.e., when using...), Figure 3 As shown in the different colors and line curves, changes in the value of the thermal lens cause variations in the spot radius at most locations within the resonant cavity, but the location of the Ti:sapphire laser crystal (see...) Figure 3 The waist spot (within the black vertical dashed line shown in the image) hardly changes, which ensures relatively stable power during laser amplification.

[0116] Experiments conducted using a laser built according to this cavity design revealed that amplified laser output could be achieved. Water cooling of the crystals was employed, and when two crystals were pumped with a 30W green laser at a repetition rate of 10kHz, a Ti:sapphire laser output of >5W could be achieved without crystal damage, indicating effective thermal management. Using photodiodes and oscilloscopes to detect light leakage in the regenerative amplification device's cavity mirrors allowed for the measurement of the laser's pulse oscillation and lead-out curves. Figure 4 The spectrum and power of the output laser obtained in the experiment are as follows: Figure 5.

[0117] This embodiment uses a two-color planar pump mirror, so the unreplaced concave mirror does not have to be two-color.

[0118] Example 2

[0119] This embodiment is another exemplary description of the water-cooled femtosecond laser regeneration amplification device of the present invention.

[0120] like Figure 2 The laser optical path shown is replaced with a red light focusing lens 21. Figure 1 The second concave mirror 4 in the middle can be omitted. Figure 1 The positions of the first and second bicolor plane pump mirrors in the image, and can be determined by... Figure 2 The first concave mirror 2 and the third concave mirror 6 are replaced with a first bicolor concave pump mirror 22 and a second bicolor concave pump mirror 23, both coated with a green light transmission film, to make green light pass through more easily. The first green light focusing mirror 14 and the second green light focusing mirror 15 are used to focus the pump laser; they can be collinear with the intracavity laser or at a certain angle to it, thus preventing it from passing through the two concave mirrors. The rest are consistent with... Figure 1 Similarly, this scheme can also obtain... Figure 1 Consistent laser output effect.

[0121] This embodiment does not use a two-color planar pump mirror, where the two unreplaced concave mirrors are two-color concave pump mirrors.

[0122] In this embodiment, the concave mirror can also be replaced with a red light lens, wherein the preferred option is to replace only the middle red light lens.

[0123] While the effects of some embodiments have been shown above, those skilled in the art should understand that, based on the concept of the invention, other embodiments not specifically shown or other technical solutions of the invention not shown in the embodiments can also achieve the same technical effects as those claimed in the summary section:

[0124] This invention uses two laser crystals and selects specific laser crystal materials, which can reduce the thermal load on the laser crystals. By designing a resonant cavity, it eliminates the laser instability problem caused by changes in the heat distribution in the laser crystal when the pump laser energy changes. Only a water chiller is needed to cool the laser crystals. The use of dual Pockels cells makes laser import and export more convenient.

[0125] Although the invention has been described to a certain extent, it is apparent that appropriate variations can be made to the various conditions without departing from the spirit and scope of the invention. It is understood that the invention is not limited to the described embodiments, but falls within the scope of the claims, which include equivalent substitutions for each of the elements.

Claims

1. A water-cooled femtosecond laser regeneration and amplification device, characterized in that, The water-cooled femtosecond laser regeneration and amplification device includes: a resonant cavity, a laser crystal, a pump optical path, a laser input / output assembly, and a synchronization circuit; The laser crystal is made of two pieces, and its material is either titanium-doped sapphire laser crystal or yttrium aluminum garnet-doped crystal, with titanium-doped sapphire laser crystal being the most preferred.

2. The water-cooled femtosecond laser regeneration and amplification device according to claim 1, characterized in that, The resonant cavity includes: an end mirror, a concave mirror, and a bicolor planar pump mirror; wherein... The number of end mirrors is 2; The number of concave mirrors is 0 to 3, preferably 1 to 3, more preferably 2 to 3, and most preferably 3; and / or The number of the two-color planar pump mirrors is 0 to 2, preferably 0 or 2; Preferably, when the number of the two-color planar pump mirrors is 0, a red light focusing lens is used instead of the one concave mirror; More preferably, the optional, unalternative concave mirror is a bicolor concave pump mirror; and / or More preferably, the number of red light focusing lenses is 1 to 3, and most preferably 1.

3. The water-cooled femtosecond laser regeneration and amplification device according to claim 2, characterized in that: The end mirror is selected from one or more of the following: plane mirror, concave mirror, convex mirror, preferably plane mirror and / or concave mirror, and most preferably 0-degree plane mirror; The bandwidth of the film layer of the end mirror is 750nm to 1150nm, preferably 750nm to 1000nm, and more preferably 750nm to 850nm; The concave mirror is a concave reflecting mirror, and the concave reflecting mirror is preferably a 0-degree concave reflecting mirror; The concave mirror has a film bandwidth of 750nm to 1150nm, preferably 750nm to 1000nm, and more preferably 750nm to 850nm. The curvature of the concave mirror is 150–1000 mm, preferably 200–800 mm, more preferably 250 mm and / or 500 mm; and / or The dual-color planar pump mirror is a dual-color planar pump mirror with double-sided coating.

4. The water-cooled femtosecond laser regeneration and amplification device according to claim 3, characterized in that, The intracavity coating of the dual-color planar pump mirror includes a 0-degree reflective coating and a 0-degree transmissive coating, while the outer cavity coating of the dual-color planar pump mirror is a 0-degree transmissive coating; wherein... The 0-degree reflective film has a bandwidth of 750nm to 1150nm, preferably 750nm to 1000nm, and more preferably 750nm to 850nm; and / or The bandwidth of the 0-degree transmission film is 500nm to 550nm, preferably 505nm to 540nm, and more preferably 515nm to 532nm.

5. The water-cooled femtosecond laser regeneration and amplification apparatus according to any one of claims 1 to 4, characterized in that, The pump optical path includes: a pump laser and a green light focusing lens; wherein... The number of green light focusing lenses is 2 to 6, preferably 2 to 4, and most preferably 2; Preferably, the pump optical path further includes: a green light guide mirror and / or a green light beam splitter; More preferably, the number of green light guide mirrors is 1 to 10, more preferably 2 to 4, and most preferably 2; and / or More preferably, the number of green beam splitters is one.

6. The water-cooled femtosecond laser regeneration and amplification device according to claim 5, characterized in that: The pump laser is a green laser or a blue laser, with a green laser being the most preferred. The wavelength of the pump laser is 500nm to 550nm, preferably 505nm to 540nm, and more preferably 515nm to 532nm; The green light guide mirror is a coated optical lens, and the reflectivity of the coated optical lens to the pump laser is 99% to 100%, preferably 99.5% to 100%, and more preferably 99.9% to 100%. The green beam splitter is an optical lens, and the transmission-reflection beam splitting ratio of the pump laser by the optical lens is 40% to 60%, preferably 45% to 55%, and most preferably 50%; and / or The green light focusing lens is a coated optical lens, and the transmittance of the coated optical lens to the pump laser is 99% to 100%, preferably 99.5% to 100%, and more preferably 99.9% to 100%.

7. The water-cooled femtosecond laser regeneration and amplification apparatus according to any one of claims 1 to 6, characterized in that, The laser import / export assembly includes: a thin-film polarizer and a Pockel cell; wherein... The number of the thin-film polarizers is 2 to 4, preferably 2 to 3, and most preferably 2; and / or The number of Pockels is 1 to 2, with 2 being the most preferred.

8. The water-cooled femtosecond laser regeneration and amplification device according to claim 7, characterized in that: The thin-film polarizer is an optical polarizer that reflects S-polarized laser light and transmits P-polarized laser light; and / or The Pockel cell is an electro-optic switch containing an electro-optic crystal, which generates a 1 / 4 waveplate phase delay on the laser crystal when a voltage is applied.

9. The water-cooled femtosecond laser regeneration and amplification apparatus according to any one of claims 1 to 8, characterized in that, The synchronization circuit is used to provide a time synchronization circuit signal for the operation of the water-cooled femtosecond laser regeneration amplification device, and is preferably an electronic synchronization delay device; Preferably, the synchronization circuit divides the input oscillator laser pulse radio frequency signal into at least three output channels, and can independently tune the delay and gate width of the output electronic signal of each channel.

10. A method for amplifying femtosecond lasers, characterized in that, The method uses the water-cooled femtosecond laser regeneration amplification device according to any one of claims 1 to 9 to amplify the femtosecond laser; Preferably, the method includes: When the water-cooled femtosecond laser regeneration amplification device is in the off state, the water-cooled femtosecond laser regeneration amplification device does not generate laser light; When the water-cooled femtosecond laser regeneration amplification device is in a spontaneous oscillation state, laser oscillation is generated in the resonant cavity; When the water-cooled femtosecond laser regeneration amplification device is in laser amplification mode, the ultrafast laser injected into the water-cooled femtosecond laser regeneration amplification device is amplified and extracted.

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