A compact high-power ultra-short pulse optical parametric amplification device

Abstract

The application provides a compact high-power ultra-short pulse optical parametric amplification device, which is sequentially provided with a glass array, a first blazed grating pair, a slit, a first mirror and a second blazed grating pair along the light path direction; the application controls femtosecond laser to pass through the ultra-thin glass array for spectral broadening, utilizes the grating pair for pulse width compression and utilizes the adjustable slit for frequency width selection, thereby realizing wide-range continuous tuning of optical parameters such as wavelength, pulse width and power of the ultrafast femtosecond laser, and being particularly suitable for high-power hundred femtosecond and sub-hundred femtosecond laser. The device can efficiently convert the incident femtosecond laser, the pulse width and the spectral bandwidth can be continuously adjusted by a large margin, and the stability of the laser output is significantly improved compared with the mode of realizing spectral broadening by using femtosecond laser through high-pressure inert gas; and the device is particularly suitable for being used as a light source parameter tuning in an ultra-high time resolution spectrum test and an ultrafast laser processing system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ultrafast laser technology, more particularly, it relates to a compact high-power ultrashort pulse optical parametric amplification device. BACKGROUND

[0002] Ultra-short pulse laser, also known as ultrafast laser, generally refers to pulse laser with pulse width in picosecond (ps), femtosecond (fs) or even sub-femtosecond level. The ultrafast laser has ultra-high instantaneous power and ultra-short pulse width, and has wide application in micro-nano processing and transient spectroscopy.

[0003] In the process of laser micro-nano processing, the ultrafast laser acts on the surface and interior of different materials to break chemical bonds and realize "cold processing". However, due to the diversity of materials, the bond energy and absorption energy gap of different materials are different, which inevitably leads to the need of different laser parameter combinations (wavelength, pulse width and power, etc.) for different materials to achieve the desired processing effect. Therefore, it is necessary to regulate the parameters of the laser output. Similarly, in the process of transient spectroscopy research, the energy band structure, absorption cross section and dynamic signal lifetime of different materials are different, and the wavelength, pulse width and power of the excitation light need to be optimally combined to achieve the best extraction of dynamic signals.

[0004] Among the currently commercialized optical parametric tuning or amplification products, the optical parametric amplifier (OPA) and the nonlinear optical parametric amplifier (NOPA) of Lithuania are the first choices. Two laser giants in the United States, Coherent and Spectra-Physics, directly purchase these two products from Lithuania and assemble and sell them. However, these two products are mainly aimed at the output of titanium-sapphire femtosecond lasers. They have less application in the field of laser processing. In addition, the OPA is mainly aimed at the tuning of wavelength and cannot realize the tuning of pulse width and power. As for the NOPA, although it can compress the pulse width of the laser, it adopts the scheme of laser crystal spectral broadening and compression. In the case of low nonlinear optical conversion efficiency (usually 10%−30%), the output power is also low, and it is generally not used in the process of laser processing. Especially, these two products are expensive, and are usually equipped in laboratories of universities and research institutes. The currently commercialized OPA and NOPA can also reach several millijoules in input power, but the conversion efficiency of ultra-wideband light through nonlinear effect is low. SUMMARY

[0005] In view of the deficiencies in the prior art, the purpose of the present application is to provide a compact high-power ultrashort pulse optical parametric amplification device to overcome the shortcomings of the existing OPA that cannot realize the tuning of pulse width and power and the existing NOPA that has low output power in the case of low nonlinear optical conversion efficiency.

[0006] The above technical purpose of the present application is achieved by the following technical solution: a compact high-power ultra-short pulse optical parametric amplification device, which is sequentially provided with a glass array, a first blazed grating pair, a slit, a first mirror, a second blazed grating pair along the direction of the light path.

[0007] The glass array is configured to receive incident femtosecond laser and perform nonlinear spectral broadening on the incident femtosecond laser to generate super-wideband white light.

[0008] The first blazed grating pair is configured to diffract the super-wideband white light to generate spatially continuous parallel light bands.

[0009] The slit is configured to select a light beam with a preset central wavelength and a preset bandwidth range from the parallel light bands.

[0010] The first mirror is configured to reflect the light beam passing through the slit and adjust the reflection direction of the light beam to transmit the light beam to the second blazed grating pair.

[0011] The second blazed grating pair is configured to receive and compress the light beam reflected by the first mirror to generate outgoing laser, and is further configured to perform dispersion compensation on the received light beam to achieve pulse width compression.

[0012] In one embodiment, the glass array includes at least two groups of glass, each group of glass including two glass pieces arranged in sequence along the propagation direction of the incident femtosecond laser to achieve nonlinear broadening by the incident femtosecond laser passing through each glass piece in sequence; and the angle between the surface of each glass piece and the incident femtosecond laser is located at the Brewster angle.

[0013] In one embodiment, the two glass pieces in the glass group are arranged in a V shape to enable the incident femtosecond laser to propagate along the original light path after passing through the two glass pieces in the glass group in sequence.

[0014] In one embodiment, the installation position of the glass is constrained by the power of the incident femtosecond laser at the installation position, specifically including:

[0015]

[0016] wherein, is the critical power of the self-focusing effect generated by the glass; is the power of the incident femtosecond laser at the installation position of the glass; and the distance between any two adjacent glass pieces is kept at a minimum distance under the premise of satisfying the power constraint of the incident femtosecond laser.

[0017] In one embodiment, further comprising: an inert gas sealed cavity; the inert gas sealed cavity is arranged along the propagation direction of the incident femtosecond laser, and the slide array is arranged inside the inert gas sealed cavity along the propagation direction of the incident femtosecond laser;

[0018] The inert gas sealed cavity is filled with one of helium, neon, argon, krypton or xenon, and the gas pressure in the inert gas sealed cavity is .

[0019] In one embodiment, the inert gas sealed cavity is provided with an incident through hole and an exit through hole;

[0020] The first slide in the slide array covers the incident through hole;

[0021] The last slide in the slide array covers the exit through hole;

[0022] The included angle between the first slide in the slide array and the incident femtosecond laser Satisfies:

[0023]

[0024] Wherein, is the Brewster angle of the air and the slide interface; is the Brewster angle of the slide and the inert gas interface;

[0025] The included angle between the last slide in the slide array and the incident femtosecond laser Satisfies:

[0026]

[0027] Wherein, is the Brewster angle of the inert gas and the slide interface; is the Brewster angle of the slide and the air interface.

[0028] In one embodiment, a diaphragm is further arranged between the slide array and the first blazed grating pair for shielding the halo formed by the incident femtosecond laser after diffraction, and a through hole is arranged at the center of the diaphragm to allow the ultra-wideband white light located in the central region of the incident femtosecond laser to pass through the through hole and then enter the first blazed grating pair.

[0029] In one embodiment, a concave mirror is further arranged between the diaphragm and the first blazed grating pair for focusing the divergent ultra-wideband white light passing through the diaphragm into parallel ultra-wideband white light.

[0030] In one embodiment, the slit comprises a first light shield and a second light shield; the first light shield and the second light shield are both capable of sliding adjustment, and the sliding directions of the first light shield and the second light shield are perpendicular to the propagation direction of the parallel light bands;

[0031] The positions of the first light shield and the second light shield are both controlled by motor driving, so as to realize continuous adjustment of the slit position and the slit width.

[0032] In one embodiment, the first blaze grating pair and the second blaze grating pair are the same blaze grating pair.

[0033] The first blaze grating pair comprises:

[0034] A first blaze grating is configured to diffract the ultra-wideband white light into light bands which are continuously distributed in space;

[0035] A second blaze grating is configured to adjust the propagation angle of the light bands, so as to generate parallel light bands which are continuously distributed in space;

[0036] The included angle between the first blaze grating and the ultra-wideband white light is a Littrow angle; the second blaze grating is slidingly arranged, and the sliding distance of the second blaze grating is controlled by motor driving, so as to adjust the optical path of light of each wavelength in the light bands;

[0037] The second blaze grating is also configured to receive the light beam reflected by the first reflector and reversely transmit the light beam to the first blaze grating; the first blaze grating is also configured to compress the light beam to generate an outgoing femtosecond laser.

[0038] In summary, the present application has the following beneficial effects: a compact high-power ultrashort pulse optical parametric amplification device is sequentially provided with a glass array, a first blazed grating pair, a slit, a first mirror, and a second blazed grating pair along the direction of the optical path; the glass array is used for receiving incident femtosecond laser and performing nonlinear spectral broadening on the incident femtosecond laser to generate ultrabroadband white light; the first blazed grating pair is used for diffracting the ultrabroadband white light to generate spatially continuous parallel light bands; the slit is used for selecting a light beam with a preset central wavelength and a preset bandwidth range from the parallel light bands; the first mirror is used for reflecting the light beam passing through the slit and adjusting the reflection direction of the light beam to deliver the light beam to the second blazed grating pair; and the second blazed grating pair is used for receiving and compressing the light beam reflected by the first mirror to generate outgoing laser, and is also used for performing dispersion compensation on the received light beam to achieve pulse width compression; the present application controls the femtosecond laser to pass through the ultrathin glass array for spectral broadening, uses the grating pair for pulse width compression, and uses the adjustable slit for frequency width selection, thereby realizing a wide range of continuous tuning of optical parameters such as wavelength, pulse width, and power of the ultrashort femtosecond laser, and being particularly suitable for high-power hundred femtosecond and sub-hundred femtosecond lasers. The device can efficiently convert the incident femtosecond laser, and the pulse width and spectral bandwidth can be greatly continuously adjustable. Compared with the method of realizing spectral broadening by using a femtosecond laser through a high-pressure inert gas, the stability of the laser output is significantly improved; and the device is particularly suitable as a light source parameter tuning in an ultrahigh time resolution optical spectrum test and an ultrashort laser processing system. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is a structural schematic diagram of a compact high-power ultrashort pulse optical parametric amplification device of the present application.

[0040] Figure 2 It is a schematic diagram of light propagation in the case of four glass sheets arranged in parallel.

[0041] Figure 3 It is a schematic diagram of light propagation in the case of four glass sheets arranged in a V shape in the present application.

[0042] Figure 4 It is a structural schematic diagram of the present application in which the four glass sheets are installed in an inert gas sealed cavity.

[0043] Figure 5 It is a calculation schematic diagram of the rotation angle of the first mirror in the present application.

[0044] In the figure: 11, first glass sheet; 12, second glass sheet; 21, first blazed grating; 22, second blazed grating; 3, slit; 4, first mirror; 5, outgoing mirror; 6, concave mirror; 7, second mirror; 8, inert gas sealed cavity. DETAILED DESCRIPTION

[0045] In order to make the objects, features and advantages of the present application more clear, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings. Several embodiments of the present application are shown in the drawings. However, the present application can be realized in many different forms and is not limited to the embodiments described herein.

[0046] The present application is described in detail below with reference to the accompanying drawings and embodiments.

[0047] In order to facilitate those skilled in the art to understand the technical solutions of the present patent, first, the prior art in the art is described: ultra-short pulse laser, also known as ultrafast laser, generally refers to pulse laser with pulse width in picosecond (ps), femtosecond (fs) or even sub-femtosecond level. The ultrafast laser has ultra-high instantaneous power and ultra-short pulse width, so it has wide application in micro-nano processing, transient spectroscopy and other fields.

[0048] OPA (Optical Parametric Amplifier, Optical Parametric Amplifier) is a device based on nonlinear optical effect, mainly used for amplifying and wavelength tuning of laser signal in a specific wavelength range. The main working principle of OPA relies on the optical parametric amplification effect of nonlinear crystal. OPA produces different frequency components in the output light through interaction with pump light. The working principle of OPA mainly includes: through the nonlinear process, the input signal interacts with the pump light, thereby generating new signal light (output light). This process usually occurs in a nonlinear crystal, which uses its nonlinear properties to amplify the signal light (or enhance the weak light signal). The gain process of OPA mainly affects the intensity of the signal light, and does not directly change the time characteristics (pulse width) of the light. Although in some cases, OPA will produce some dispersion effect through interaction with pump light, but this usually does not significantly change the pulse width. The gain efficiency of OPA is related to the power of pump light and the initial intensity of signal light. By increasing the power of pump light, the power of signal light can be improved, but the gain amplitude of OPA does not accurately control the power. The output power of OPA is related to the power of pump light and the efficiency of nonlinear crystal, so its output power is determined by the characteristics of pump and crystal.

[0049] The gain process of a NOPA (Non-Linear Optical Parametric Amplifier) system involves the conversion of pump light energy into signal light and idler light. The phase matching condition in the nonlinear optical process determines the energy exchange efficiency between the pump light and the signal light. Due to the strict requirements of the phase matching condition on the wavelength and the beam shape, perfect matching cannot be achieved, thereby limiting the effective conversion of energy. Different nonlinear crystal materials have different nonlinear coefficients, losses, and bandwidth characteristics. For efficient spectral broadening and compression, it is very important to select the appropriate crystal material, but these materials usually need to work at a lower conversion efficiency. Due to the low nonlinear optical conversion efficiency of the NOPA, the output signal power is usually relatively low. Usually only a few millijoules.

[0050] Embodiment One

[0051] To solve the above problems, the present application provides a compact high-power ultra-short pulse optical parametric amplification device, as shown in Figures 1-3 , arranged in order along the light path direction: a glass plate array, a first blazed grating pair, a slit 3, a first mirror 4, and a second blazed grating pair.

[0052] The glass plate array is used to receive incident femtosecond laser and perform nonlinear spectral broadening on the incident femtosecond laser to generate ultra-wideband white light.

[0053] The first blazed grating pair is used to diffract the ultra-wideband white light to generate spatially continuous parallel light bands.

[0054] The slit 3 is used to select a light beam with a preset central wavelength and a preset bandwidth range from the parallel light bands.

[0055] The first mirror 4 is used to reflect the light beam passing through the slit 3 and adjust the reflection direction of the light beam to deliver the light beam to the second blazed grating pair.

[0056] The second blazed grating pair is used to receive and compress the light beam reflected by the first mirror 4 to generate outgoing laser, and is also used to perform dispersion compensation on the received light beam to achieve pulse width compression.

[0057] ​In practical applications, a plurality of glass sheets are arranged in the glass sheet array, and the glass sheet array is capable of nonlinearly broadening the incident laser when receiving the incident laser. When the incident laser passes through the glass sheet, the instantaneous phase of the pulse changes, causing the spectrum to expand to the low and high frequency sides, respectively, thereby broadening the pulse of the incident laser and generating ultra-wideband white light. Under the condition of fixing the parameters of the incident laser, the broadening range of the ultra-wideband white light is related to the material of the glass sheet, the thickness of the glass sheet, the gas pressure in the environment where the glass sheet is located, and the type of gas.

[0058] The first blazed grating pair is used to diffract the ultra-wideband white light, and a spatially continuous light band is generated. In order to select a light beam with a preset central wavelength and a preset bandwidth range from the light band, the first blazed grating pair is also used to adjust the spatially continuous light band to a parallel light band. By adjusting the distance inside the first blazed grating pair, the optical path can also be compensated, so that the optical path of light with a longer wavelength is lengthened, and the optical path of light with a shorter wavelength is shortened, so that light of each wavelength can be kept in a closer position to compress the pulse width of the incident laser.

[0059] The slit 3 is used to select a light beam with a preset central wavelength and a preset bandwidth range from the parallel light band. Since the parallel light band is spatially continuous, adjusting the position of the slit 3 can correspondingly select a light band with a predetermined central wavelength. According to the Fourier transform limit formula, and By adjusting the bandwidth and wavelength position, the effect of adjusting the pulse width can be achieved. The central position of the slit 3 corresponds to the central wavelength, and the width of the slit 3 is proportional to the wavelength bandwidth of the reflected light band. At the same time, the change of the wavelength bandwidth will also cause the change of the output laser power. Therefore, the central wavelength, bandwidth, pulse width, and power of the laser can be continuously tuned.

[0060] The first mirror 4 is used to adjust the angle of the bandwidth light band passing through the slit 3, so that the propagation direction of the bandwidth light band and the direction of the incident light are separated from each other.

[0061] The second blazed grating pair is used to receive and compress the light beam reflected by the first mirror 4 to generate an outgoing laser. The second blazed grating pair is also used to compensate for the dispersion of the received light beam to achieve a pulse width compression light beam.

[0062] In summary, the application provides a compact high-power ultra-short pulse optical parametric amplification device. The device uses femtosecond laser to perform spectral broadening and grating compression to achieve frequency width selection through an ultra-thin glass sheet, and is particularly suitable for high-power hundred femtosecond and sub-hundred femtosecond lasers. The input light conversion efficiency of the device is high, and the pulse width and spectral bandwidth can be continuously adjusted. After frequency doubling and difference frequency, the wavelength adjustable range can be wider. Compared with the method of using femtosecond laser to achieve spectral broadening through high-pressure inert gas only, the stability of the laser output is greatly improved. At the same time, compared with the scheme of using expensive ultra-wideband chirped mirrors for compression, the product price is greatly reduced. It is particularly suitable as a light source for parametric tuning in ultra-high time resolution spectral testing and ultrafast laser processing systems.

[0063] In one embodiment, the glass sheet array comprises: at least two groups of glass sheet groups, each glass sheet group comprising two glass sheets arranged in sequence along the propagation direction of the incident femtosecond laser to achieve nonlinear broadening of the incident femtosecond laser by sequentially passing through each glass sheet; and the angle between the surface of each glass sheet and the incident femtosecond laser is located at the Brewster's Angle.

[0064] In practical applications, the Brewster's Angle refers to the angle at which the reflected light is completely polarized and the transmitted light has the maximum power when the incident angle meets a certain condition when the light is incident from one medium to another medium. The specific angle of the Brewster's Angle is related to the refractive indices of the two media, and specifically satisfies:

[0065]

[0066] wherein, represents the Brewster's Angle, that is, the angle between the incident light and the interface; is the refractive index of the incident medium; is the refractive index of the transmitted medium. When light is incident from air to a glass sheet, part of the light is reflected and part of the light is transmitted. The intensity of the reflected light and the transmitted light depends on the incident angle. At the Brewster's Angle, the intensity of the reflected light is minimized and the intensity of the transmitted light is maximized. Therefore, controlling the angle between the glass sheet and the incident femtosecond laser can effectively improve the transmission efficiency of the incident femtosecond laser.

[0067] In one embodiment, the first glass sheet 11 and the second glass sheet 12 in the glass sheet group are arranged in a V shape so that the incident femtosecond laser can propagate along the original light path after sequentially passing through the two glass sheets in the glass sheet group.

[0068] In practical applications, as Figure 2 , Figure 3As shown in the figure, two of the two glass pieces in each glass piece group are arranged in a V shape, which can make the laser deflected in the glass piece with thickness to make a slight optical path correction, avoiding the existence of a large position offset between the optical path and the original incident femtosecond laser, affecting the integration of the equipment.

[0069] In one embodiment, the installation position of the glass piece is subject to the power of the incident femtosecond laser at the installation position, specifically including:

[0070]

[0071] Wherein, The critical power of the self-focusing effect of the glass piece; The power of the incident femtosecond laser at the installation position of the glass piece; the distance between any two adjacent glass pieces is kept at a minimum distance under the premise of meeting the incident femtosecond laser power constraint.

[0072] In practical applications, when the ultra-short laser propagates in the air, due to the high intensity of the laser, the refractive index of the air will change, usually increase, which will cause the laser beam to focus, further increase its intensity, and form a kind of self-focusing effect. After focusing, the ultra-short laser pulse will usually form a high-intensity concentrated spot in the near focal point area, and as the laser propagates, the focal point will expand. However, the high intensity and nonlinear effect of the laser pulse can cause the laser to re-focus or deform in the area away from the focal point, forming a layered propagation effect, that is, the layering effect of the laser propagating in the air, so the laser usually focuses, diverges and focuses alternately in the propagation path of the laser, and a large number of focal spots will be formed in the propagation path of the laser. Again, the thinner the laser beam, the higher the peak power of the laser, and the more obvious the nonlinear effect of the interaction between the laser and the glass piece. The peak power cannot be too high, and the peak power that is too high will damage the glass piece. When setting the position of the glass piece, the glass piece is usually set near the focal point position to balance the relationship between the nonlinear effect and the peak power. Specifically, the position of the glass piece can be adjusted to maximize the spectral broadening at the position of the glass piece.

[0073] Based on the layering effect of the nonlinear laser, the placement position of the glass piece needs to be determined based on the power of the incident femtosecond laser at each position , and the critical power of the self-focusing effect of the glass piece , that is, the placement position needs to meet . In addition, in order to improve the integration of the equipment and reduce the size of the equipment, the distance between the two glass pieces needs to be kept at a minimum value when the glass pieces are placed under the condition of meeting the incident power. The position of the glass piece can also be adjusted to maximize the spectral broadening at the position of the glass piece.

[0074] In one embodiment, the glass slide is made of one or more of BBO crystal, sapphire crystal, and quartz glass.

[0075] In practical applications, the peak power threshold of the input ultrashort laser pulse is controlled by adjusting the power of the input ultrashort laser. The power threshold for achieving self-phase modulation (SPM) on a glass slide is greater than that required. The refractive index of the material through which the glass slide or laser light passes exhibits nonlinear characteristics; the refractive index *n* of an optical material is related to the light intensity *I*. When the electric field strength changes, the refractive index of the material also changes, and the phase of the light wave passing through the medium also changes; this is called SPM (Spectral Pulsation). SPM causes frequency adjustment, resulting in spectral broadening. Its frequency shift... It can be expressed as follows:

[0076]

[0077]

[0078] in, It is the average power of the laser. It is the repetition frequency of the laser. It is the area of ​​the focal spot. The duration of a single pulse. It is the laser wavelength. For effective area, For effective length, The nonlinear refractive index of the medium. Simultaneously, the power threshold of the input laser. It must be greater than the critical power at which the slide produces a self-focusing effect. However, it is less than twice the latter, specifically satisfying the following conditions:

[0079]

[0080]

[0081] Where λ is the laser wavelength. For linear refractive index, The nonlinear refractive index of the medium. By varying the materials and thicknesses of glass slides, the spectral bandwidth can be broadened by 10 times or more. In particular, the design of ultrathin micron-sized glass slides is more suitable for high-peak-power femtosecond laser spectral broadening than currently used spectral broadening designs such as sapphire, CaF2, and water films.

[0082] In one embodiment, the thickness of the slide of the slide group array can be adjusted according to the pulse energy of the incident femtosecond laser. From the perspective of bandwidth expansion and supercontinuum light quality, the higher the power, the thinner the slide, so that the laser passes through the thickness of the medium, which helps to reduce the divergence of the laser and improve the beam quality. In the present embodiment, the thickness of the slide is between . Incident angle satisfies the Brewster angle. With the current commercial titanium sapphire laser as the light source, the output laser pulse width is , the output power is , and the repetition frequency is . The input power that can be achieved by the device is . By adjusting the focal length of the laser passing through the concave mirror, the highest peak power at the shorter end can reach the order of . By adjusting the position of the slide at the focal point, the slide can be placed at the optimal peak power position to obtain the best expansion effect and conversion efficiency without damaging the slide. Thus, after passing through group of slides, continuous white light in the range of can be generated. The conversion efficiency of the ultra-wideband white light generated by the input laser can reach . When injecting atmospheric pressure of inert gas He in the slide cavity, the spectral width can reach . In the present application, the spectrum of the slide expanded by 1.5 He gas pressure, the light signal passing through the slit 3, reflected by the first reflecting mirror 4, and then compressed by the blazed grating, the pulse width can be continuously tuned between sub-5 femtoseconds and picoseconds, and the center wavelength and bandwidth can be continuously tuned between . Combined with the laser after frequency doubling and difference frequency, the integrated frequency selection of the slit 3-the first reflecting mirror 4 can realize a large continuous adjustable range from ultraviolet 250 nm to infrared 1700 nm.

[0083] In one embodiment, as shown in Figure 4 , it further comprises: an inert gas sealed cavity 8; the inert gas sealed cavity 8 is arranged along the propagation direction of the incident femtosecond laser, and the slide array is arranged inside the inert gas sealed cavity 8 along the propagation direction of the incident femtosecond laser;

[0084] The inert gas sealed cavity 8 is filled with one of helium, neon, argon, krypton or xenon, and the gas pressure in the inert gas sealed cavity 8 is .

[0085] Specifically, in practical applications, the spectral broadening effect is related to the medium through which the ultrafast laser passes. In inert gas, the broadening effect is more pronounced compared to air. Furthermore, in gaseous media, the higher the pressure, the greater the impact on spectral broadening. Therefore, by filling the inert gas sealed cavity 8 with inert gas and controlling its pressure, the broadening effect of the ultrafast laser can be further improved. During the laser's passage through the glass slide assembly, both the glass slide and the inert gas can act as nonlinear media, contributing to laser broadening. In particular, the nonlinear refractive index of the inert gas increases with increasing gas pressure, thus providing a positive gain effect on spectral broadening.

[0086] In one embodiment, such as Figure 4 As shown, the inert gas sealing cavity 8 is provided with an inlet through hole and an outlet through hole;

[0087] The first glass slide in the glass slide array is placed over the incident through-hole;

[0088] The last glass slide in the glass slide array is placed over the exit through-hole;

[0089] The angle between the first glass slide in the glass slide array and the incident femtosecond laser satisfy:

[0090]

[0091] in, Brewster's angle at the air-glass slide interface; Brewster's angle is the angle at the interface between the glass slide and the inert gas.

[0092] The angle between the last glass slide in the glass slide array and the incident femtosecond laser. satisfy:

[0093]

[0094] in, Brewster's angle is the angle between the inert gas and the glass slide. Brewster's angle is the angle between the glass slide and the air.

[0095] Specifically, filling the inert gas sealed cavity 8 with high-pressure inert gas not only enhances the spectral broadening effect of the ultrafast laser but also alters the Brewster angle from the glass slide into the high-pressure inert gas. In other words, on the first glass slide, the first Brewster angle at which the ultrafast femtosecond laser enters the slide from the air... And the second Brewster angle of the ultrafast femtosecond laser emitted from the glass slide into the inert gas. The two Brewster angles are different, and the average of the two Brewster angles can be taken to maximize the transmittance of the femtosecond laser. Similarly, the angle of the last glass sheet needs to be determined based on the average of the two Brewster angles.

[0096] In the inert gas sealed cavity 8, in order to avoid the high-pressure gas crushing the glass sheet on the incident through hole, the size of the incident through hole and the exit through hole needs to be controlled within a predetermined size range, and the predetermined size is usually 1mm-3mm.

[0097] When the laser passes through the inert gas medium and is refracted on the surface and inside of the glass sheet, the refractive index of the inert gas is close to that of air. However, the refractive index of the inert gas increases with the increase of the gas pressure, which has a fine adjustment effect on the direction of the laser exiting through the glass sheet group.

[0098] Change of the refractive index of the inert gas , satisfies:

[0099]

[0100] wherein , and The refractive index under standard conditions, the gas pressure and the temperature. and are the expansion coefficient and the Celsius temperature of the gas, respectively. is the increase or change of the gas pressure. By changing the gas pressure, the refractive index also changes proportionally, thereby modulating the Brewster angle. Under the same laser input parameters, replacing the inert gas He with Ne gas or even Xe gas with a larger nonlinear refractive index, the spectral broadening amplitude will further increase to .

[0101] In an embodiment, the glass sheet is detachably arranged, so that the material and thickness of the glass sheet can be adjusted according to the pulse energy of the incident laser. From the perspective of bandwidth broadening and supercontinuum light quality, the higher the power, the thinner the glass sheet, so that the thickness of the laser passing through the medium is small, which is beneficial to reduce the divergence of the laser and improve the beam quality.

[0102] In an embodiment, a diaphragm is further arranged between the glass sheet array and the first pair of blazed gratings, for shielding the light halo formed by the incident femtosecond laser after diffraction. A through hole is formed in the center of the diaphragm, so that the ultra-wideband white light located in the central region of the incident femtosecond laser passes through the through hole and then enters the first pair of blazed gratings.

[0103] The superfast femtosecond laser is spectrally broadened after passing through the glass sheet, and color halos are generated around the laser. These color halos may interfere with subsequent light after entering the grating. To solve this problem, an optical stop with a through hole is needed to shield the color halos around the laser and only allow the white light in the middle of the superfast femtosecond laser to pass through, while also adjusting the laser power.

[0104] In one embodiment, a concave mirror 6 is further arranged between the optical stop and the first blazed grating pair to focus the divergent super-wideband white light into parallel super-wideband white light.

[0105] Due to the hierarchical effect of the superfast laser propagating in the medium, the superfast laser will be divergent after passing through the last glass sheet. Therefore, the superfast laser after passing through the optical stop will still be divergent. In order to enable the superfast laser to propagate smoothly, a concave mirror 6 is further arranged in the propagation path of the superfast laser to focus the divergent super-wideband white light into parallel super-wideband white light. The spot diameter on the concave mirror 6 is The following constraints need to be met:

[0106]

[0107] Wherein is the maximum spot diameter on the concave mirror 6; is the focal length of the concave mirror 6; is the central wavelength of the incident light beam; is the focal spot radius at the position of the last glass sheet.

[0108] In one embodiment, in order to adjust the angle of the light beam reflected by the concave mirror 6, a second mirror 7 is further arranged after the concave mirror 6 to adjust the propagation direction of the parallel super-wideband white light.

[0109] In one embodiment, the slit 3 includes a first light shield and a second light shield; both the first light shield and the second light shield can be adjusted by sliding, and the sliding direction of the first light shield and the second light shield is perpendicular to the propagation direction of the parallel light band; the position of the first light shield and the position of the second light shield are both controlled by a motor drive to realize continuous adjustment of the position and width of the slit 3.

[0110] The sliding positions of the first and second light-shielding pieces are controlled by a motor drive, realizing continuous adjustment of the position and width of the slit 3, with high flexibility and adaptability. The sliding direction of the light-shielding pieces is perpendicular to the propagation direction of the parallel light bands, which can efficiently cut the target spectral region and avoid horizontal interference, thereby improving the adjustment efficiency. The motor drive is a servo motor or a stepper motor, which can accurately control the rotation angle of the motor based on the number of pulses, thereby realizing high-precision adjustment of the position and width of the slit 3 to meet different experimental requirements. The motor drive supports automatic adjustment, simplifies the operation process, reduces manual intervention, and is particularly suitable for application scenarios that require frequent switching of spectral settings, thereby significantly improving the convenience and efficiency of the system.

[0111] In actual applications, the adjustment of the slit 3 can be manual or electric, and the adjustment of the slit 3 can be achieved by changing the position of the center point of the slit 3 to select the position of the center wavelength, or adjusting the width of the slit 3 to select the bandwidth of the light signal passing through the slit 3. The selection of the position of the center wavelength requires the overall adjustment of the upper and lower light-shielding pieces of the slit 3, and the simultaneous movement of the two light-shielding pieces to select the center wavelength of the slit 3 while keeping the phase position unchanged. The selection of the bandwidth is to control the relative position of the upper and lower light-shielding pieces of the slit 3 to adjust the width of the slit 3. According to the time-frequency uncertainty principle, the bandwidth of the ultrafast laser is inversely proportional to the pulse width, so by selecting the bandwidth of the light band formed by the expansion of the ultrafast laser, the pulse width of the ultrafast laser can be indirectly controlled. In this application, the pulse width of the light signal passing through the slit 3, reflected by the first mirror 4, and then compressed by the blazed grating can be continuously tuned from sub-5 femtoseconds to picoseconds, and the center wavelength and bandwidth can be continuously tuned within By combining the frequency-doubled and frequency-difference lasers, the slit 3 and the first mirror 4 can be integrated to realize a large range of continuous adjustment from ultraviolet to infrared bands.

[0112] In one embodiment, the first blazed grating pair and the second blazed grating pair are the same blazed grating pair;

[0113] The first blazed grating pair includes:

[0114] A first blazed grating 21 is configured to diffract the ultra-wideband white light into a light band that is continuously distributed in space;

[0115] A second blazed grating 22 is configured to adjust the propagation angle of the light band to generate a parallel light band that is continuously distributed in space;

[0116] The angle between the first blazed grating 21 and the ultra-wideband white light is the Littrow angle; the second blazed grating 22 is slidably configured, and the sliding distance of the second blazed grating 22 is controlled by a motor drive to adjust the optical path of each wavelength of light in the light band;

[0117] The second blazed grating 22 is also used to receive the light beam reflected by the first reflector 4 and to transmit the light beam in the opposite direction to the first blazed grating 21. The first blazed grating 21 is also used to compress the light beam to generate an outgoing femtosecond laser.

[0118] In practical applications, a first blazed grating is used to diffract ultra-wideband white light into a spatially continuous light band, and a second blazed grating is used to parallelize the light band to generate a spatially continuous parallel light band, such as... Figure 1 As shown, although there is a certain angle between the multiple rays emitted from the first blazed grating, the second blazed grating can adjust the angular relationship between the rays, transforming the angled rays into parallel rays. In applications requiring high-precision focusing, interference, and laser beam transmission, parallel beams can improve system efficiency and controllability. By converting beams with a certain angular relationship into parallel rays, the propagation direction and coherence of the light are optimized. Through two-stage grating processing, the first grating achieves spectral decomposition, and the second grating completes the task of beam parallelization, allowing the light source configuration to adapt to different optical system design requirements. Beam parallelization also facilitates the calculation of the corresponding position and size for controlling the slit 3 when selecting a portion of the light signal for pulse width compression. Furthermore, beam parallelization facilitates the calculation of optical path length to adjust the angle of the first reflector 4, achieving ultrafast laser pulse width compression. Additionally, the second blazed grating can slide, and the distance between the second blazed grating and the first grating can be adjusted to adjust the optical path length for different wavelength bands, thereby compressing the ultrafast laser pulse width.

[0119] In one embodiment, the angle between the first blazed grating 21 and the ultrawideband white light conforms to the Littrow angle.

[0120] In practical applications, the grating constant is typically tens to thousands of divisions per millimeter. By adjusting the grating spacing, the pulse width of the broadened spectrum can be compressed. The angle of incidence on the blazed grating satisfies the Littrow angle and satisfies... ,in It is a diffraction order. It's the wavelength. It is the grating constant, which is the number of grating lines per millimeter. It is the angle of incidence. The diffraction efficiency of the grating is highest when the angle of incidence equals the Littrow angle.

[0121] In one embodiment, the first mirror 4 is rotatably arranged to adjust the spot position of the light beam passing through the slit 3 to the first grating to ensure the output of the laser and prevent the laser from returning to the original path.

[0122] Specifically, as shown in Figure 5 ; the rotation angle of the first mirror 4 needs to be determined according to the offset of the spot, as shown in Figure 5 ; the super-wideband white light irradiated on the first grating will form a spot A, after the light beam is reflected by the first mirror 4, a spot B will be formed on the second grating, and after being reflected by the second grating to the first grating, a spot C will be formed; therefore, the rotation angle of the first mirror 4 satisfies:

[0123]

[0124]

[0125]

[0126] wherein, represents the distance between the spot A and the spot C, is the vertical distance between the two gratings; represents the distance from the foot D of the perpendicular line from the center point of the spot B to the second grating to the spot A. According to the distance between the two gratings and the distance of the movement of the spot formed by the outgoing laser on the first grating , the rotation angle of the first mirror 4 can be calculated .

[0127] In one embodiment, an exit mirror 5 is further included, which is arranged after the first blazed grating 21 to receive the outgoing femtosecond laser and adjust the direction and angle of the outgoing femtosecond laser.

[0128] In summary, the present application provides a high-power ultra-short pulse optical parametric amplification device. The present application controls the femtosecond laser to pass through the ultra-thin glass sheet for spectral broadening, the grating pair for pulse width compression, and the frequency width selection for optical parametric tuning, which is particularly suitable for high-power hundred femtosecond and sub-hundred femtosecond lasers. The device of the present application can efficiently convert the incident femtosecond laser, and the pulse width and spectral bandwidth can be continuously adjustable. Compared with the method of realizing spectral broadening by high-pressure inert gas using femtosecond laser, the stability of the laser output is greatly improved, and compared with the scheme of using expensive ultra-wideband chirped mirrors for compression, the product price is greatly reduced; it is particularly suitable as a light source parameter tuning in ultra-high time resolution spectrum test and ultrafast laser processing system.

[0129] Any combination of the technical features in the above embodiments can be made, and for the sake of brevity, not all possible combinations of the technical features in the above embodiments are described, however, as long as the combination of the technical features does not exist contradictions, it should be considered as the scope of the present disclosure.

[0130] The above description is only the preferred embodiments of the present application, and the protection scope of the present application is not limited to the above embodiments. Any technical solutions falling within the concept of the present application shall be considered as the protection scope of the present application. It should be noted that, for ordinary skilled in the art, some improvements and refinements without departing from the principles of the present application shall be considered as the protection scope of the present application.

Claims

1. A compact, high-power ultrashort pulse optical parametric amplifier, characterized in that, The following components are arranged sequentially along the optical path: a glass slide array, a first pair of blazed gratings, a slit, a first mirror, and a second pair of blazed gratings; The glass slide array is used to receive the incident femtosecond laser and to perform nonlinear spectral broadening on the incident femtosecond laser to generate ultrawideband white light. The glass slide array includes at least two groups of glass slides, each group of glass slides including two glass slides, the glass slides being arranged sequentially along the propagation direction of the incident femtosecond laser, so that the incident femtosecond laser passes through each glass slide sequentially to achieve nonlinear broadening; the angle between the surface of each glass slide and the incident femtosecond laser is located at Brewster's angle. The two glass slides in the glass slide group are arranged in a V-shape so that the incident femtosecond laser can propagate along the original optical path after passing through the two glass slides in the glass slide group in sequence. The mounting position of the glass slide is constrained by the power of the incident femtosecond laser at that mounting position, specifically including: in, The critical power for the glass slide to produce a self-focusing effect; The power of the incident femtosecond laser at the mounting position of the glass slide; the distance between any two adjacent glass slides is kept to a minimum while satisfying the power constraint of the incident femtosecond laser; in, It is the average power of the laser. It is the repetition frequency of the laser. It is the area of ​​the focal spot. The duration of a single pulse; Where λ is the laser wavelength. For linear refractive index, The nonlinear refractive index of the medium; The first pair of blazed gratings is used to diffract the ultrawide white light to generate parallel light bands that are continuously distributed in space. A slit is used to select a beam of light with a preset center wavelength and a preset bandwidth range from the parallel light band; A first reflecting mirror is used to reflect the light beam passing through the slit and adjust the reflection direction of the light beam to transmit it to the second blazed grating pair. The rotation angle of the first reflecting mirror needs to be determined according to the offset of the light spot. When ultra-wideband white light shines on the first blazed grating of the first blazed grating pair, it will form a light spot A. After the first reflecting mirror reflects the light beam, it will form a light spot B on the second blazed grating of the first blazed grating pair. After being reflected by the second blazed grating of the first blazed grating pair back to the first blazed grating of the first blazed grating pair, it will form a light spot C. Therefore, the rotation angle of the first reflecting mirror... satisfy: in, This represents the distance between light spot A and light spot C. The vertical distance between the two gratings; The distance D represents the foot of the perpendicular line drawn from the center point of light spot B to the second blazed grating aligned with the first blazed grating, and the distance from light spot A. The second blazed grating pair is used to receive and compress the beam reflected by the first reflector to generate an outgoing laser. The second blazed grating pair is also used to perform dispersion compensation on the received beam to achieve pulse width compression. The blazed gratings of the first blazed grating pair and the blazed gratings of the second blazed grating pair are both reflective blazed gratings; It also includes: an inert gas sealed cavity; the inert gas sealed cavity is arranged along the propagation direction of the incident femtosecond laser, and the glass slide array is arranged inside the inert gas sealed cavity along the propagation direction of the incident femtosecond laser; The inert gas sealed cavity is filled with one of helium, neon, argon, krypton, or xenon, and the gas pressure in the inert gas sealed cavity is [insert pressure here]. ; The inert gas sealing cavity is provided with an inlet through hole and an outlet through hole; The first glass slide in the glass slide array is placed over the incident through-hole; The last glass slide in the glass slide array is placed over the exit through-hole; The angle between the first glass slide in the glass slide array and the incident femtosecond laser satisfy: in, Brewster's angle at the air-glass slide interface; Brewster's angle is the angle at the interface between the glass slide and the inert gas. The angle between the last glass slide in the glass slide array and the incident femtosecond laser. satisfy: in, Brewster's angle is the angle between the inert gas and the glass slide. Brewster's angle at the glass slide-air interface; An aperture is also provided between the glass slide array and the first blazed grating pair to block the halo formed by the diffraction of the incident femtosecond laser. A through hole is provided in the center of the aperture so that the ultrawideband white light located in the central region of the incident femtosecond laser passes through the through hole and enters the first blazed grating pair. A concave reflector is also provided between the aperture and the first blazed grating pair to focus the divergent ultrawide white light passing through the aperture into parallel ultrawide white light. The slit includes a first light-blocking plate and a second light-blocking plate; both the first light-blocking plate and the second light-blocking plate are adjustable by sliding, and the sliding direction of the first light-blocking plate and the second light-blocking plate is perpendicular to the propagation direction of the parallel light strip. The positions of the first and second light-shielding plates are both controlled by motor drive, enabling continuous adjustment of the slit position and slit width.

2. The compact high-power ultrashort pulse optical parametric amplifier according to claim 1, characterized in that, The first blazed grating pair and the second blazed grating pair are the same blazed grating pair; The first blazed grating pair includes: A first blazed grating is used to diffract the ultrawideband white light into a spatially continuous light band; The second blazed grating is used to adjust the propagation angle of the light band and generate parallel light bands that are continuously distributed in space. The angle between the first blazed grating and the ultra-wideband white light is the Littrow angle; the second blazed grating is a sliding grating, and the sliding distance of the second blazed grating is controlled by a motor drive to adjust the optical path of each wavelength of light in the light band; The second blazed grating is also used to receive the light beam reflected by the first reflector and to transmit the light beam in reverse to the first blazed grating. The first blazed grating is also used to compress the light beam to generate an outgoing femtosecond laser.

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