Device and method for generating GHz repetition frequency high-power femtosecond green light and ultraviolet laser

Abstract

The invention belongs to the field of all-solid-state ultrafast laser, and discloses a GHz repetition frequency high-power femtosecond green light and ultraviolet laser generation device and method, and the method comprises the steps: a pumping source outputs fundamental frequency femtosecond laser with the repetition frequency greater than 1GHz; generating femtosecond green light from the fundamental frequency femtosecond laser through a frequency doubling effect; splitting the residual femtosecond laser and the frequency doubling femtosecond green light in the emergent light of the first frequency doubling crystal to obtain a residual femtosecond laser light path and a femtosecond green light path which are parallel to each other; adjusting the time delay of the transmission process of the residual fundamental frequency femtosecond laser to enable the time delay to coincide with the femtosecond green light time in the femtosecond green light path; combining the emergent light of the remaining femtosecond laser light path and the emergent light of the femtosecond green light path; and performing sum frequency on the residual fundamental frequency femtosecond laser and the femtosecond green light after beam combination to generate ultraviolet femtosecond laser. According to the invention, femtosecond green light output with GHz repetition frequency and high output power and ultraviolet femtosecond laser output with GHz repetition frequency and high output power are realized at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of all-solid-state ultrafast lasers, and in particular to a device and method for generating high-power femtosecond green light and ultraviolet lasers with a GHz repetition frequency. Background Art

[0002] Green light and ultraviolet femtosecond lasers with shorter wavelengths have the advantages of high single-photon energy and high temporal resolution, and are widely used in fields such as ultrafast phenomena in physics and chemistry, biomedical microscopy, and ultra-fine micro-nano processing.

[0003] Taking femtosecond laser micromachining as an example, near-infrared femtosecond lasers with a wavelength of approximately 1μm are currently the most commonly used processing light source. However, shorter wavelength green and ultraviolet lasers have a smaller diffraction limit, which facilitates higher peak power density. These lasers offer advantages in OLED module cutting, FPC material cutting and drilling, composite thin film processing, and the processing of transparent materials such as sapphire. They can also achieve submicron-scale processing such as micropores, optical waveguides, and photonic crystals in materials such as semiconductors, glass, and polymers. Furthermore, shorter wavelength green and ultraviolet lasers offer the advantages of high single-photon energy and high temporal resolution, making them widely used in fields such as ultrafast phenomena in physics and chemistry, biomedical microscopy, and ultrafine micro-nanofabrication. Combining green or ultraviolet femtosecond lasers with high GHz repetition rates offers even greater advantages in laser processing and biomedicine. Traditional low-repetition-rate femtosecond laser processing only offers the advantage of high-quality processing, but the ablation rate is lower compared to nanosecond and other long-pulse laser processing. GHz-repetition-rate femtosecond lasers, on the other hand, can operate in pulse train mode, utilizing the ablation cooling effect. This involves using a sufficient number of sub-pulses to gradually raise the material temperature to near the ablation threshold, which then causes ablation. However, because the interval between sub-pulses is often less than the thermal relaxation time of the material (1 ns (repetition rate greater than 1 GHz), heat still accumulates in the material, maintaining the ablation temperature without excessive excess energy. Therefore, using GHz-repetition-rate femtosecond green or ultraviolet lasers as micro-nanoprocessing light sources can not only improve ablation efficiency but also ensure processing quality. For example, high-power GHz femtosecond green light can be used as a pump source for optical parametric oscillators, extending the wavelength of GHz femtosecond lasers into the visible, long-wave near-infrared, and mid-infrared ranges through nonlinear frequency conversion, providing a light source for biophotonics applications such as two-photon microscopy.

[0004] To obtain GHz repetition rate femtosecond green or ultraviolet lasers, the most common approach is to frequency-double or triple a GHz repetition rate femtosecond laser with a wavelength near 1μm. However, high GHz repetition rates often result in lower single-pulse energy and peak power, which conflicts with the high peak power required for nonlinear processes such as frequency doubling or tripling. Consequently, there have been no reports of direct frequency-doubling studies using GHz repetition rate femtosecond oscillators in recent years.

[0005] Therefore, how to provide an experimental device and method that can achieve high-efficiency GHz femtosecond laser frequency doubling and generate femtosecond green light or ultraviolet femtosecond laser is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0006] In response to the above research status and existing problems, the present invention provides a device and method for generating high-power femtosecond green light and ultraviolet laser with a GHz repetition frequency.

[0007] The present invention provides a device for generating high-power femtosecond green light and ultraviolet laser with a GHz repetition rate, comprising a pump source arranged according to the propagation direction of the GHz repetition rate pump light, a first frequency-doubled optical path, a beam splitting optical path, a remaining femtosecond laser optical path, a femtosecond green light optical path, a beam combining optical path, and a second frequency-doubled optical path; wherein,

[0008] The pump source is an all-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser, which is used to output a fundamental frequency femtosecond laser with a repetition rate greater than 1 GHz;

[0009] The first frequency doubling optical path includes a first frequency doubling crystal arranged in the propagation direction of the GHz repetition frequency pump light, and is used to generate femtosecond green light by frequency doubling effect of the fundamental frequency femtosecond laser;

[0010] The beam splitting optical path is used to split the remaining femtosecond laser and the frequency-doubled femtosecond green light in the light emitted by the first frequency-doubled crystal to obtain a parallel remaining femtosecond laser optical path and a femtosecond green light optical path;

[0011] The remaining femtosecond laser optical path includes a roof prism for adjusting the time delay of the remaining fundamental frequency femtosecond laser transmission process so that it coincides with the time of the femtosecond green light incident on the second frequency-doubled optical path by the femtosecond green light optical path;

[0012] The beam combining optical path is used to combine the outgoing light of the remaining femtosecond laser optical path and the outgoing light of the femtosecond green light optical path;

[0013] The second frequency doubling optical path includes a second frequency doubling crystal arranged in the propagation direction of the combined light beam, which is used to perform sum frequency conversion on the remaining fundamental frequency femtosecond laser and femtosecond green light after the combined beam to generate ultraviolet femtosecond laser.

[0014] Preferably, the all-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser is a LD-pumped Yb-doped gain medium Kerr lens mode-locked femtosecond oscillator with a central wavelength of 1037 nm, an average output power greater than 5 W, and a pulse width of 120 fs.

[0015] Preferably, the first frequency doubling crystal is used to generate femtosecond green light with a wavelength of 518 nm from a fundamental frequency femtosecond laser through a frequency doubling effect.

[0016] Preferably, the first frequency doubling optical path includes:

[0017] A first half-wave plate is used to adjust the polarization state of the fundamental frequency femtosecond laser output by the all-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser;

[0018] Isolator, used to isolate reflected light;

[0019] The second half-wave plate is used to adjust the polarization state of the fundamental frequency femtosecond laser;

[0020] a thin film polarizer, used to cooperate with the second half-wave plate to adjust the transmitted laser power;

[0021] The first reflector and the second reflector are used to adjust the transmission direction of the fundamental frequency femtosecond laser so that the outgoing light of the second reflector is parallel to the incident light of the first reflector and has an opposite direction;

[0022] a first focusing mirror, configured to receive the fundamental frequency femtosecond laser reflected by the second reflecting mirror and focus the laser onto the first frequency-doubling crystal;

[0023] The first frequency doubling crystal is used to generate femtosecond green light by frequency doubling the fundamental frequency femtosecond laser;

[0024] The second focusing mirror is used to collimate the remaining fundamental frequency femtosecond laser of the first frequency-doubling crystal and the generated femtosecond green light.

[0025] Preferably, the splitting light path includes:

[0026] a first dichroic mirror, configured to receive the outgoing light of the first frequency-doubling crystal, having a 45° reflectivity of the remaining fundamental frequency femtosecond laser in the outgoing light higher than a set value, and a transmittance of the femtosecond green light higher than a set value, and to split the remaining fundamental frequency femtosecond laser and the frequency-doubling femtosecond green light into beams to obtain reflected remaining fundamental frequency femtosecond laser and transmitted femtosecond green light;

[0027] The second dichroic mirror is used to receive the femtosecond green light transmitted by the first dichroic mirror, and its reflectivity at 45° to the femtosecond green light is higher than a set value, and its transmittance to the fundamental frequency femtosecond laser is higher than a set value, and splits the remaining fundamental frequency femtosecond laser and the doubled frequency femtosecond green light in the transmitted light to obtain reflected femtosecond green light.

[0028] Preferably, the remaining femtosecond laser light path includes:

[0029] The third reflector and the fourth reflector are used to adjust the transmission direction of the remaining fundamental frequency femtosecond laser so that the outgoing light of the fourth reflector is parallel to the incident light of the third reflector and has an opposite direction;

[0030] The third half-wave plate is used to adjust the polarization state of the remaining fundamental frequency femtosecond laser so that it meets the phase matching condition with the second frequency-doubling crystal;

[0031] a roof prism for receiving the output light of the third half-wave plate and adjusting the time delay of the remaining fundamental frequency femtosecond laser transmission process so as to make it coincide with the time of the femtosecond green light incident on the second frequency-doubled optical path by the femtosecond green light optical path;

[0032] a fifth reflecting mirror, used to adjust the transmission direction of the remaining fundamental frequency femtosecond laser so that it is parallel to and in the same direction as the incident light of the fourth reflecting mirror;

[0033] The third focusing mirror is used to receive the remaining fundamental frequency femtosecond laser reflected by the fifth reflecting mirror and focus it onto the second frequency-doubled optical path.

[0034] Preferably, the femtosecond green light path includes:

[0035] a sixth reflecting mirror, used for adjusting the transmission direction of the femtosecond green light;

[0036] The fourth half-wave plate is used to adjust the polarization state of the femtosecond green light so that it meets the phase matching condition with the second frequency-doubling crystal;

[0037] a fourth focusing mirror, used for focusing the generated femtosecond green light onto the second frequency-doubled light path;

[0038] The seventh reflector is used to adjust the transmission direction of the femtosecond green light so that it is parallel to and opposite to the incident light of the sixth reflector.

[0039] Preferably, the beam combining optical path includes: a third dichroic mirror, used to receive the remaining fundamental frequency femtosecond laser emitted by the remaining femtosecond laser optical path and the femtosecond green light emitted by the femtosecond green light optical path, and the reflectivity of the remaining fundamental frequency femtosecond laser at 45° is higher than a set value, and the transmittance of the femtosecond green light is higher than a set value.

[0040] Preferably, the second frequency-doubling optical path includes:

[0041] The second frequency-doubling crystal is used to provide a sum frequency effect for the remaining fundamental frequency femtosecond laser and femtosecond green light after beam combining to generate ultraviolet femtosecond laser;

[0042] The fourth dichroic mirror is used to receive the output light of the second frequency-doubling crystal, has a transmittance higher than a set value for the remaining fundamental frequency femtosecond laser and femtosecond green light, and a reflectivity higher than a set value for ultraviolet light at 45°, and is used to output the generated ultraviolet femtosecond laser.

[0043] Preferably, the reflectivity of the first half-wave plate, the second half-wave plate and the third half-wave plate in the 1020-1060 nm band is less than 0.1%, and can provide a half phase delay in this band.

[0044] Preferably, the first reflector, the second reflector, the third reflector, the fourth reflector and the fifth reflector are coated with a 45-degree high-reflection film for the 970-1100 nm wavelength band, and the reflectivity is greater than 99.9%.

[0045] Preferably, the reflectivity of the first focusing lens, the second focusing lens and the third focusing lens in the 400-1100 nm band is less than 0.5%; and the focal length is 100 mm.

[0046] Preferably, the reflectivity of the fourth focusing lens in the 400-1100 nm band is less than 0.5%; and the focal length is 150 mm.

[0047] Preferably, the first frequency-doubling crystal is a bismuth borate crystal, a barium metaborate crystal or a lithium triborate crystal; preferably, the first frequency-doubling crystal is a lithium triborate crystal with a light transmission length of 4 mm.

[0048] Preferably, the first dichroic mirror and the second dichroic mirror are coated with a 45-degree high-reflection film for 1000-1100nm laser, and the reflectivity is greater than 99.9%; and are also coated with an anti-reflection film for 488-532nm laser, and the reflectivity is less than 2%.

[0049] Preferably, the sixth reflector and the seventh reflector are coated with a 45-degree high-reflection film for 488-532 nm lasers, and the reflectivity is greater than 99.9%.

[0050] Preferably, the second frequency-doubling crystal is a bismuth borate crystal, a barium metaborate crystal or a lithium triborate crystal; preferably, the second frequency-doubling crystal is a bismuth borate crystal with a light transmission length of 1 mm.

[0051] Preferably, the third dichroic mirror has high reflection to fundamental frequency laser with a wavelength of 1037 nm and high transmission to laser with a wavelength of 518 nm.

[0052] Preferably, the fourth dichroic mirror has high transmittance to lasers with wavelengths of 1037 nm and 518 nm, and high reflectivity to lasers with a wavelength of 346 nm.

[0053] The present invention provides a method for generating GHz repetition rate high-power femtosecond green light and ultraviolet laser according to the device for generating GHz repetition rate high-power femtosecond green light and ultraviolet laser, comprising the following steps:

[0054] S1: All-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser emits fundamental frequency femtosecond laser with a repetition rate greater than 1 GHz;

[0055] S2: The fundamental frequency femtosecond laser generates femtosecond green light and remaining fundamental frequency femtosecond laser through the frequency doubling effect of the first frequency doubling crystal;

[0056] S3: Splitting the femtosecond green light and the remaining fundamental frequency femtosecond laser light to obtain parallel remaining femtosecond laser light paths and femtosecond green light light paths;

[0057] S4: adjusting the time delay of the remaining fundamental frequency femtosecond laser transmission process through the roof prism so that it coincides with the time of the femtosecond green light incident on the second frequency-doubled light path by the femtosecond green light path;

[0058] S5: Combining the output lights of the remaining femtosecond laser light path and the femtosecond green light light path;

[0059] S6: The remaining fundamental frequency femtosecond laser and femtosecond green light after the beam combination are summed by the second frequency doubling crystal to generate ultraviolet femtosecond laser.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] The present invention applies an all-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser to frequency conversion, which can generate high-power femtosecond green light and femtosecond ultraviolet lasers. Compared with the traditional solution of using a MHz low repetition rate laser as a frequency doubling and tripling pump source, the repetition rate of green and ultraviolet femtosecond lasers can be increased to above 1 GHz, proving that although the GHz repetition rate Kerr lens mode-locked femtosecond laser has a lower single pulse energy, it can still be used for high-efficiency frequency conversion research.

[0062] The device has the advantages of high power output, compact structure and stable operation, and has wide application value in femtosecond laser processing, nonlinear microscopy, ultraviolet femtosecond optical frequency comb and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only embodiments of the present invention. Those skilled in the art can also derive other drawings based on the provided drawings without inventive effort.

[0064] Figure 1 1 is a schematic structural diagram of a GHz repetition rate high-power femtosecond green and ultraviolet laser device provided by an embodiment of the present invention;

[0065] Figure 2 is a spectrum diagram of the fundamental frequency femtosecond laser provided by an embodiment of the present invention;

[0066] Figure 3 Schematic diagram of the repetition frequency of the fundamental frequency femtosecond laser provided by an embodiment of the present invention;

[0067] Figure 4 This is a graph showing the corresponding relationship between the output power and conversion efficiency of femtosecond green light generated by frequency doubling provided by an embodiment of the present invention and the output power of the incident fundamental frequency femtosecond laser;

[0068] Figure 5 This is a spectrum diagram of femtosecond green light generated by frequency doubling provided by an embodiment of the present invention;

[0069] Figure 6 This is a graph showing the corresponding relationship between the output power and conversion efficiency of the ultraviolet femtosecond laser generated by frequency tripling provided by an embodiment of the present invention and the output power of the incident fundamental frequency femtosecond laser;

[0070] Figure 7 This is a spectrum diagram of ultraviolet femtosecond laser generated by frequency tripling provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0071] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0072] The following is combined with Figure 1 The application principle of the present invention is described in detail.

[0073] The first aspect of the embodiment of the present invention provides a device for generating high-power femtosecond green light and ultraviolet laser with a GHz repetition rate, such as Figure 1 As shown, it includes a pump source arranged according to the propagation direction of the GHz repetition frequency pump light, a first frequency-doubled optical path, a beam splitting optical path, a remaining femtosecond laser optical path, a femtosecond green light optical path, a beam combining optical path, and a second frequency-doubled optical path; wherein,

[0074] The pump source is an all-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser 1, which is used to output fundamental frequency femtosecond laser with a repetition rate greater than 1 GHz;

[0075] The first frequency doubling optical path includes a first frequency doubling crystal 9 arranged in the propagation direction of the GHz repetition frequency pump light, which is used to generate femtosecond green light by frequency doubling effect of the fundamental frequency femtosecond laser;

[0076] A beam splitting optical path, used for splitting the remaining femtosecond laser and the frequency-doubled femtosecond green light in the light emitted by the first frequency-doubling crystal 9 to obtain a parallel remaining femtosecond laser optical path and a femtosecond green light optical path;

[0077] The remaining femtosecond laser optical path includes a roof prism 16, which is used to adjust the time delay of the remaining fundamental frequency femtosecond laser transmission process so that it coincides with the time of the femtosecond green light incident on the second frequency-doubled optical path by the femtosecond green light optical path;

[0078] A beam combining optical path, used for combining the outgoing light of the remaining femtosecond laser optical path and the femtosecond green light optical path;

[0079] The second frequency doubling optical path includes a second frequency doubling crystal 24 arranged in the propagation direction of the combined light beam, which is used to perform sum frequency conversion on the remaining fundamental frequency femtosecond laser and femtosecond green light after the combined beam to generate ultraviolet femtosecond laser.

[0080] In one embodiment, the all-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser 1 is a LD-pumped Yb-doped gain medium Kerr lens mode-locked femtosecond oscillator with a central wavelength of 1037 nm, an average output power greater than 5 W, and a pulse width of 120 fs. Figure 2-3 As shown in the figure, they are the spectrum diagram and repetition frequency schematic diagram of the fundamental frequency femtosecond laser.

[0081] In one embodiment, the first frequency doubling crystal 9 is used to generate femtosecond green light with a wavelength of 518 nm from a fundamental frequency femtosecond laser through a frequency doubling effect.

[0082] In one embodiment, the first frequency doubling optical path includes:

[0083] The first half-wave plate 2 is used to adjust the polarization state of the fundamental frequency femtosecond laser output by the all-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser 1;

[0084] The isolator 3 is used to isolate the reflected light to prevent the mode-locked state of the femtosecond laser 1 from being interrupted;

[0085] The second half-wave plate 4 is used to adjust the polarization state of the fundamental frequency femtosecond laser;

[0086] The thin film polarizer 5 is used to cooperate with the second half-wave plate 4 to adjust the transmitted laser power;

[0087] The first reflector 6 and the second reflector 7 are used to adjust the transmission direction of the fundamental frequency femtosecond laser so that the outgoing light of the second reflector 7 is parallel to the incident light of the first reflector 6 and in the opposite direction;

[0088] The first focusing mirror 8 is used to receive the fundamental frequency femtosecond laser reflected by the second reflecting mirror 7 and focus it onto the first frequency doubling crystal 9;

[0089] A first frequency doubling crystal 9 is used to generate femtosecond green light by frequency doubling effect of the fundamental frequency femtosecond laser, and optionally, to generate femtosecond green light with a wavelength of 518 nm by frequency doubling effect of the fundamental frequency femtosecond laser;

[0090] The second focusing lens 10 is used to collimate the remaining fundamental frequency femtosecond laser of the first frequency doubling crystal 9 and the generated femtosecond green light.

[0091] During the specific implementation of this embodiment, the 1037nm femtosecond laser output by the all-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser 1 is incident on the thin-film polarizer 5 through the first half-wave plate 2, the isolator 3, and the second half-wave plate 4. The laser power passing through the thin-film polarizer 5 can be controlled by rotating the second half-wave plate 4, thereby achieving the purpose of regulating power. The transmitted 1037nm femtosecond laser then passes through the first reflector 6, the second reflector 7, and the first focusing mirror 8 in sequence, and is focused into the first frequency doubling crystal 9, generating a femtosecond green light with a wavelength of 518nm through the frequency doubling effect; the second focusing mirror 10 collimates the 518nm femtosecond green light and the incompletely converted 1037nm femtosecond laser. Figure 4-5 As shown, there are the corresponding relationship diagrams of the femtosecond green light output power and conversion efficiency generated by the doubled frequency and the output power of the incident fundamental frequency femtosecond laser, as well as the spectrum of the femtosecond green light.

[0092] In one embodiment, the split beam path includes:

[0093] The first dichroic mirror 11 is used to receive the output light of the first frequency-doubling crystal 9, and has a 45° reflectivity of the remaining fundamental frequency femtosecond laser in the output light that is higher than a set value, and a transmittance of the femtosecond green light that is higher than a set value, and splits the remaining fundamental frequency femtosecond laser and the frequency-doubling femtosecond green light into reflected remaining fundamental frequency femtosecond laser and transmitted femtosecond green light;

[0094] The second dichroic mirror 12 is used to receive the femtosecond green light transmitted by the first dichroic mirror 11. Its reflectivity at 45° to the femtosecond green light is higher than the set value, and its transmittance to the fundamental frequency femtosecond laser is higher than the set value. It splits the remaining fundamental frequency femtosecond laser and the doubled frequency femtosecond green light in the transmitted light to obtain reflected femtosecond green light.

[0095] In one embodiment, the remaining femtosecond laser optical path includes:

[0096] The third reflecting mirror 13 and the fourth reflecting mirror 15 are used to adjust the transmission direction of the remaining fundamental frequency femtosecond laser so that the outgoing light of the fourth reflecting mirror 15 is parallel to the incident light of the third reflecting mirror 13 and has an opposite direction;

[0097] The third half-wave plate is located between the third reflector 13 and the fourth reflector 15 in the optical path, and is used to adjust the polarization state of the remaining fundamental frequency femtosecond laser so that it meets the phase matching condition with the second frequency doubling crystal 24;

[0098] The roof prism 16 is used to receive the output light of the third half-wave plate and adjust the time delay of the remaining fundamental frequency femtosecond laser transmission process so that it coincides with the time of the femtosecond green light incident on the second frequency-doubled light path;

[0099] The fifth reflecting mirror 17 is used to adjust the transmission direction of the remaining fundamental frequency femtosecond laser so that it is parallel to and in the same direction as the incident light from the fourth reflecting mirror 15;

[0100] The third focusing mirror 18 is used to receive the remaining fundamental frequency femtosecond laser reflected by the fifth reflecting mirror 17 and focus it onto the second frequency-doubled optical path.

[0101] During the specific implementation of this embodiment, the incompletely converted 1037nm femtosecond laser collimated by the second focusing mirror 10 then passes through the first dichroic mirror 11, the second dichroic mirror 12, the third reflector 13, the third half-wave plate, the fourth reflector 15, the roof prism 16, and the fifth reflector 17 in sequence, wherein the fourth reflector 15, the roof prism 16, and the fifth reflector 17 are combined to adjust the propagation distance of the 1037nm femtosecond laser, and then is focused by the third focusing mirror 18 and reflected by the third dichroic mirror 23 into the second frequency-doubled optical path.

[0102] In one embodiment, the femtosecond green light path includes:

[0103] A sixth reflecting mirror 19 is used to adjust the transmission direction of the femtosecond green light;

[0104] The fourth half-wave plate 20 is used to adjust the polarization state of the femtosecond green light so that it meets the phase matching condition with the second frequency doubling crystal 24;

[0105] A fourth focusing mirror 21 is used to focus the generated femtosecond green light onto the second frequency-doubled light path;

[0106] The seventh reflector 22 is used to adjust the transmission direction of the femtosecond green light so that it is parallel to and opposite to the incident light of the sixth reflector 19 .

[0107] During the specific implementation of this embodiment, the 518nm femtosecond green light collimated by the second focusing mirror 10 will pass through the first dichroic mirror 11, the second dichroic mirror 12, the sixth reflector 19, and the fourth half-wave plate 20 in sequence, and then be focused by the fourth focusing mirror 21 and reflected by the seventh reflector 22 before passing through the combined optical path to reach the second frequency-doubled optical path.

[0108] In one embodiment, the beam combining optical path includes a third dichroic mirror 23 for receiving the remaining fundamental frequency femtosecond laser light emitted from the remaining femtosecond laser optical path and the femtosecond green light emitted from the femtosecond green light optical path. The third dichroic mirror 23 has a reflectivity at 45° of greater than a set value for the remaining fundamental frequency femtosecond laser light and a transmittance of greater than a set value for the femtosecond green light. Adjusting the seventh reflector 22 and the third dichroic mirror 23 allows the spatial positions of the 518nm femtosecond green light and the 1037nm femtosecond laser light in the second frequency-doubled crystal 24 to be adjusted, respectively, to ensure spatial overlap between the two laser beams. Adjusting the position of the roof prism 16 ensures that the 518nm femtosecond green light and the 1037nm femtosecond laser light are temporally overlapped in the second frequency-doubled optical path, further generating sum frequency and outputting the sum frequency.

[0109] In one embodiment, the second frequency doubling optical path includes:

[0110] The second frequency doubling crystal 24 is used to provide a sum frequency effect for the remaining fundamental frequency femtosecond laser and femtosecond green light after beam combining, and optionally to generate ultraviolet femtosecond laser with a wavelength of 346 nm;

[0111] The fourth dichroic mirror 25 is used to receive the output light of the second frequency doubling crystal 24. Its transmittance to the remaining fundamental frequency femtosecond laser and femtosecond green light is higher than the set value, and its reflectivity to the ultraviolet light at 45° is higher than the set value, so as to output the generated ultraviolet femtosecond laser.

[0112] The 518nm femtosecond green light and the 1037nm femtosecond laser achieve temporal overlap in the second frequency-harmonic optical path, further generating sum frequency to generate ultraviolet femtosecond laser with a wavelength of 346nm, which is reflected and output by the fourth dichroic mirror 25. Figure 6-7 As shown, there are the corresponding relationship diagrams of the output power and conversion efficiency of the ultraviolet femtosecond laser generated by frequency tripling and the output power of the incident fundamental frequency femtosecond laser, as well as the spectrum of the ultraviolet femtosecond laser.

[0113] In one embodiment, the reflectivity of the first half-wave plate 2, the second half-wave plate 4, and the third half-wave plate in the 1020-1060 nm band is less than 0.1%, and can provide a half phase delay in this band.

[0114] In one embodiment, the first reflector 6 , the second reflector 7 , the third reflector 13 , the fourth reflector 15 , and the fifth reflector 17 are coated with a 45-degree high-reflection film for the 970-1100 nm wavelength band, and the reflectivity is greater than 99.9%.

[0115] In one embodiment, the reflectivity of the first focusing lens, the second focusing lens, and the third focusing lens in the 400-1100 nm wavelength range is less than 0.5%; and the focal length is 100 mm.

[0116] In one embodiment, the reflectivity of the fourth focusing lens in the 400-1100 nm wavelength range is less than 0.5% and the focal length is 150 mm.

[0117] In one embodiment, the first frequency-doubling crystal 9 and the second frequency-doubling crystal 24 are bismuth borate crystals, barium metaborate crystals, or lithium triborate crystals. Optionally, the first frequency-doubling crystal 9 is a lithium triborate crystal with a light passage length of 4 mm, and the second frequency-doubling crystal 24 is a bismuth borate crystal with a light passage length of 1 mm. In specific implementations, the crystal material can be selected from nonlinear crystals of different lengths, such as barium metaborate crystals (β-BaB2O4, BBO), lithium triborate crystals (LiB3O5, LBO), bismuth borate (BIB3O6, BIBO), etc., based on the fundamental frequency light and the desired frequency-doubling laser output parameters.

[0118] In one embodiment, the first dichroic mirror 11 and the second dichroic mirror 12 are coated with a 45-degree high-reflection film for 1000-1100 nm lasers with a reflectivity greater than 99.9%; and are also coated with an anti-reflection film for 488-532 nm lasers with a reflectivity less than 2%.

[0119] In one embodiment, the sixth reflector 19 and the seventh reflector 22 are coated with a 45-degree high-reflection film for 488-532 nm lasers, and the reflectivity is greater than 99.9%.

[0120] In one embodiment, the third dichroic mirror 23 has high reflectivity for fundamental frequency laser light with a wavelength of 1037 nm and high transmittance for laser light with a wavelength of 518 nm.

[0121] In one embodiment, the fourth dichroic mirror 25 has high transmittance to laser beams with wavelengths of 1037 nm and 518 nm, and high reflectivity to laser beams with a wavelength of 346 nm.

[0122] A second aspect of an embodiment of the present invention provides a method for generating GHz repetition rate high-power femtosecond green light and ultraviolet lasers of a device for generating GHz repetition rate high-power femtosecond green light and ultraviolet lasers according to the first aspect of the embodiment, comprising the following steps:

[0123] S1: All-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser 1 emits fundamental frequency femtosecond laser with a repetition rate greater than 1 GHz;

[0124] S2: The fundamental frequency femtosecond laser generates femtosecond green light and the remaining fundamental frequency femtosecond laser through the frequency doubling effect of the first frequency doubling crystal 9;

[0125] S3: Splitting the femtosecond green light and the remaining fundamental frequency femtosecond laser to obtain parallel remaining femtosecond laser light paths and femtosecond green light light paths;

[0126] S4: adjusting the time delay of the remaining fundamental frequency femtosecond laser transmission process through the roof prism 16 so that it coincides with the time of the femtosecond green light incident on the second harmonic frequency optical path by the femtosecond green light optical path;

[0127] S5: Combining the remaining femtosecond laser light path and the outgoing light of the femtosecond green light path;

[0128] S6: The remaining fundamental frequency femtosecond laser and the femtosecond green light after the combined beams are subjected to sum frequency conversion by the second frequency doubling crystal 24 to generate ultraviolet femtosecond laser.

[0129] The optical path propagation of the embodiment of the present invention is specifically as follows: a fundamental frequency femtosecond laser with a central wavelength of 1037 nm generated by an all-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser 1 is used as pump light, and the pump light propagates in sequence through a first half-wave plate 2, an isolator 3, a second half-wave plate 4, a thin-film polarizer 5, a first reflector 6, a second reflector 7, a first focusing mirror 8, and finally reaches a first frequency-doubling crystal 9;

[0130] The pump light undergoes a frequency doubling effect in the first frequency doubling crystal 9 to generate femtosecond green light with a central wavelength of 518 nm. The generated femtosecond green light and the unconverted pump light are separated by the first dichroic mirror 11.

[0131] The unconverted pump light passes through the second focusing mirror 10 and is reflected by the first dichroic mirror 11. It then passes through the fourth reflector 15, the third half-wave plate, the fifth reflector 17, the roof prism 16, the sixth reflector 19, the third focusing mirror 18, the third dichroic mirror 23 and reaches the second frequency doubling crystal 24.

[0132] The femtosecond green light generated by frequency doubling passes through the first dichroic mirror 11 and sequentially passes through the second dichroic mirror 12, the sixth reflector 19, the fourth half-wave plate 20, the fourth focusing mirror 21, the seventh reflector 22, the third dichroic mirror 23 to the second frequency doubling crystal 24;

[0133] By rotating the third half-wave plate and the fourth half-wave plate 20, the polarization states of the unconverted pump light and the femtosecond green light incident on the second frequency doubling crystal 24 can be adjusted respectively, so that phase matching is achieved in the second frequency doubling crystal 24, thereby improving the sum frequency generation efficiency;

[0134] By adjusting the angles of the third dichroic mirror 23 and the seventh reflector 22, the spatial positions of the unconverted pump light and the femtosecond green light incident on the second frequency-doubling crystal 24 can be adjusted respectively, so that the focal points of the focused light spots are spatially overlapped in the second frequency-doubling crystal 24;

[0135] By adjusting the front and rear positions of the roof prism 16, the transmission distance of the unconverted pump light from the first dichroic mirror 11 to the second frequency-doubling crystal 24 can be controlled, thereby controlling the arrival time of the unconverted pump light transmitted to the second frequency-doubling crystal 24, so that it can be synchronized with the femtosecond green light transmitted to the second frequency-doubling crystal 24;

[0136] The unconverted pump light and the femtosecond green light that achieve spatial synchronization, temporal synchronization, and meet phase matching conditions generate a sum frequency effect to generate ultraviolet femtosecond laser light with a central wavelength of 346 nm. The generated ultraviolet femtosecond laser light is reflected and output by the fourth dichroic mirror 25 .

[0137] The present invention directly uses a GHz repetition rate high-power Kerr lens mode-locked femtosecond laser 1 as a pump source to perform frequency conversion; the GHz repetition rate femtosecond green light and ultraviolet femtosecond laser generating device designed by the present invention has a simple structure and a compact system, and can achieve femtosecond green light output with a pulse repetition rate greater than 1 GHz and an output power greater than 2 W, and can also achieve ultraviolet femtosecond laser output with a repetition rate greater than 1 GHz and an output power greater than 0.5 W.

[0138] The above is a detailed introduction to the device and method for generating GHz repetition rate high-power femtosecond green light and ultraviolet lasers provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only intended to help understand the method and core concept of the present invention. At the same time, for those skilled in the art, according to the concept of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

[0139] In this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

Claims

1. A device for generating high-power femtosecond green and ultraviolet lasers with a GHz repetition rate, characterized by: It includes a pump source arranged in the propagation direction of the GHz repetition frequency pump light, a first frequency-doubled optical path, a beam splitting optical path, a remaining femtosecond laser optical path, a femtosecond green light optical path, a beam combining optical path, and a second frequency-doubled optical path; wherein, The pump source is an all-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser (1), which is used to output a fundamental frequency femtosecond laser with a repetition rate greater than 1 GHz; The first frequency doubling optical path comprises a first frequency doubling crystal (9) arranged in the propagation direction of the GHz repetition frequency pump light, and is used to generate femtosecond green light by frequency doubling effect from the fundamental frequency femtosecond laser; The beam splitting optical path is used to split the remaining femtosecond laser and the frequency-doubled femtosecond green light in the output light of the first frequency-doubling crystal (9) to obtain a parallel remaining femtosecond laser optical path and a femtosecond green light optical path; The remaining femtosecond laser light path includes a roof prism (16) for adjusting the time delay of the remaining fundamental frequency femtosecond laser transmission process so as to coincide with the time of the femtosecond green light incident on the second frequency-doubled light path by the femtosecond green light light path; The beam combining optical path is used to combine the outgoing light of the remaining femtosecond laser optical path and the outgoing light of the femtosecond green light optical path; The second frequency doubling optical path includes a second frequency doubling crystal (24) arranged in the propagation direction of the combined light beam, and is used for sum-frequencying the remaining fundamental frequency femtosecond laser and femtosecond green light after the combined beam to generate ultraviolet femtosecond laser.

2. The device for generating GHz repetition rate high power femtosecond green light and ultraviolet laser according to claim 1, characterized in that: The all-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser is a LD-pumped Yb-doped gain medium Kerr lens mode-locked femtosecond oscillator with a central wavelength of 1037nm, an average output power greater than 5W, and a pulse width of 120fs.

3. The device for generating GHz repetition rate high power femtosecond green light and ultraviolet laser according to claim 2, characterized in that: The first frequency doubling crystal (9) is used to generate femtosecond green light with a wavelength of 518 nm from the fundamental frequency femtosecond laser through the frequency doubling effect.

4. The device for generating GHz repetition rate high power femtosecond green light and ultraviolet laser according to claim 1, characterized in that: The first frequency-doubling optical path includes: A first half-wave plate (2) is used to adjust the polarization state of the fundamental frequency femtosecond laser output by the all-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser (1); an isolator (3), used for isolating the reflected light; A second half-wave plate (4) is used to adjust the polarization state of the fundamental frequency femtosecond laser; a thin film polarizing plate (5) for cooperating with the second half-wave plate (4) to adjust the power of the transmitted laser; The first reflecting mirror (6) and the second reflecting mirror (7) are used to adjust the transmission direction of the fundamental frequency femtosecond laser so that the outgoing light of the second reflecting mirror (7) is parallel to the incident light of the first reflecting mirror (6) and has opposite directions; a first focusing mirror (8) for receiving the fundamental frequency femtosecond laser reflected by the second reflecting mirror (7) and focusing the laser onto the first frequency-doubling crystal (9); A first frequency doubling crystal (9) is used to generate femtosecond green light by frequency doubling the fundamental frequency femtosecond laser; The second focusing mirror (10) is used for collimating the remaining fundamental frequency femtosecond laser light and the generated femtosecond green light of the first frequency doubling crystal (9).

5. The device for generating GHz repetition rate high power femtosecond green light and ultraviolet laser according to claim 1, characterized in that: The beam splitting optical path comprises: a first dichroic mirror (11) for receiving the outgoing light of the first frequency-doubling crystal (9), having a 45° reflectivity of the remaining fundamental frequency femtosecond laser in the outgoing light higher than a set value, and a transmittance of the femtosecond green light higher than a set value, and splitting the remaining fundamental frequency femtosecond laser and the frequency-doubling femtosecond green light to obtain reflected remaining fundamental frequency femtosecond laser and transmitted femtosecond green light; The second dichroic mirror (12) is used to receive the femtosecond green light transmitted by the first dichroic mirror (11), wherein the reflectivity of the second dichroic mirror to the femtosecond green light at 45° is higher than a set value, and the transmittance of the second dichroic mirror to the fundamental frequency femtosecond laser is higher than a set value, and the second dichroic mirror splits the remaining fundamental frequency femtosecond laser and the doubled frequency femtosecond green light in the transmitted light to obtain reflected femtosecond green light.

6. The device for generating GHz repetition rate high power femtosecond green light and ultraviolet laser according to claim 1, characterized in that: The remaining femtosecond laser optical path includes: The third reflecting mirror (13) and the fourth reflecting mirror (15) are used to adjust the transmission direction of the remaining fundamental frequency femtosecond laser light so that the outgoing light of the fourth reflecting mirror (15) is parallel to the incident light of the third reflecting mirror (13) and in opposite directions; A third half-wave plate (14) is used to adjust the polarization state of the remaining fundamental frequency femtosecond laser so that it satisfies a phase matching condition with the second frequency doubling crystal; A roof prism (16) is used to receive the output light of the third half-wave plate (14) and adjust the time delay of the remaining fundamental frequency femtosecond laser transmission process so that it coincides with the time of the femtosecond green light incident on the second frequency-doubled light path by the femtosecond green light path; a fifth reflecting mirror (17) for adjusting the transmission direction of the remaining fundamental frequency femtosecond laser light so that the light is parallel to and in the same direction as the incident light of the fourth reflecting mirror (15); The third focusing mirror (18) is used to receive the remaining fundamental frequency femtosecond laser reflected by the fifth reflecting mirror (17) and focus it onto the second frequency-doubled optical path.

7. The device for generating GHz repetition rate high power femtosecond green light and ultraviolet laser according to claim 1, characterized in that: The femtosecond green light path includes: a sixth reflecting mirror (19), used for adjusting the transmission direction of the femtosecond green light; A fourth half-wave plate (20) is used to adjust the polarization state of the femtosecond green light so that it satisfies a phase matching condition with the second frequency doubling crystal; a fourth focusing mirror (21), used for focusing the generated femtosecond green light onto the second frequency-doubled light path; The seventh reflector (22) is used to adjust the transmission direction of the femtosecond green light so that it is parallel to and opposite to the incident light of the sixth reflector (19).

8. The device for generating GHz repetition rate high power femtosecond green light and ultraviolet laser according to claim 1, characterized in that: The beam combining optical path comprises: a third dichroic mirror (23) for receiving the remaining fundamental frequency femtosecond laser light emitted by the remaining femtosecond laser optical path and the femtosecond green light emitted by the femtosecond green light optical path, wherein the reflectivity of the remaining fundamental frequency femtosecond laser light at 45° is higher than a set value, and the transmittance of the femtosecond green light is higher than a set value.

9. The device for generating GHz repetition rate high power femtosecond green light and ultraviolet laser according to claim 1, characterized in that: The second frequency doubling optical path includes: The second frequency doubling crystal (24) is used to provide a sum frequency effect for the remaining fundamental frequency femtosecond laser and femtosecond green light after beam combining, thereby generating ultraviolet femtosecond laser; The fourth dichroic mirror (25) is used to receive the output light of the second frequency doubling crystal (24), has a transmittance higher than a set value for the remaining fundamental frequency femtosecond laser and femtosecond green light, and has a reflectance higher than a set value for ultraviolet light at 45 degrees, and is used to output the generated ultraviolet femtosecond laser.

10. A method for generating GHz repetition rate high-power femtosecond green light and ultraviolet laser by a device for generating GHz repetition rate high-power femtosecond green light and ultraviolet laser according to any one of claims 1 to 9, characterized in that: The steps include: S1: All-solid-state high-power GHz repetition rate Kerr lens mode-locked femtosecond laser (1) emits fundamental frequency femtosecond laser with a repetition rate greater than 1 GHz; S2: The fundamental frequency femtosecond laser generates femtosecond green light and remaining fundamental frequency femtosecond laser through the frequency doubling effect of the first frequency doubling crystal (9); S3: Splitting the femtosecond green light and the remaining fundamental frequency femtosecond laser light to obtain parallel remaining femtosecond laser light paths and femtosecond green light light paths; S4: adjusting the time delay of the remaining fundamental frequency femtosecond laser transmission process through the roof prism (16) so that it coincides with the time of the femtosecond green light incident on the second frequency-doubled light path by the femtosecond green light path; S5: Combining the output lights of the remaining femtosecond laser light path and the femtosecond green light light path; S6: The remaining fundamental frequency femtosecond laser and the femtosecond green light after the combined beam are subjected to frequency summing through the second frequency doubling crystal (24) to generate ultraviolet femtosecond laser.

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