Ultrafast optical parametric oscillator cavity length locking device, laser and locking method

Abstract

The present invention provides an ultrafast optical parametric oscillator cavity length locking device, a laser and a locking method, belonging to the field of laser technology. The locking device comprises an optical module and a control circuit module, the optical module comprises an ultrafast pump source, a pump focusing mirror, an optical resonant cavity, a nonlinear crystal, a temperature-controlled furnace, a beam splitter, a dispersion element and an aperture, and the control circuit module comprises a first photodetector, a second photodetector, an amplifier, a low-pass filter, a signal generator, a servo controller, a high-voltage amplifier and piezoelectric ceramics. The present invention uses a dispersion element and an aperture to select a narrowband spectrum as a cavity locking signal, and uses the different sensitivities of different wavelengths to the cavity length to lock it at the rising edge or falling edge of the narrowband spectrum power without introducing a disturbance signal, thereby achieving stable operation of the total power of the signal light at the peak point without a modulation signal.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and in particular to an ultrafast optical parametric oscillator cavity length locking device, a laser and a locking method. Background Art

[0002] The statements in this section merely provide background art related to the present invention and do not necessarily constitute prior art.

[0003] High-power, high-repetition-rate ultrafast laser pulses have a wide range of applications, such as biophotonics, time-resolved spectroscopy, and optical frequency combs. Ultrafast optical parametric oscillators (OPOs) have attracted widespread attention due to their wide wavelength tuning range. Most OPOs are in a free-running state. Affected by group velocity dispersion, as long as the mismatch between the OPO cavity length and the pump pulse repetition frequency does not exceed a certain range, the OPO can meet the synchronous pumping conditions to keep the signal light resonant. However, under different cavity length conditions, the central wavelength, power, and pulse width of the signal light that achieves resonance are different; factors such as the disturbance of the pump source, the vibration of the cavity mirror, the change of the external environment temperature, and the disturbance of the airflow will cause the ultrafast OPO cavity length to jitter, affecting the output stability of the OPO in the free-running state, which limits the wide application of OPOs.

[0004] The stability of the resonant cavity length is the key to achieving stable output of synchronously pumped OPOs. Commonly used OPO output stability control methods are mainly divided into passive control methods and active control methods. Passive control methods include using a shockproof platform to achieve vibration isolation, adding a protective cover to isolate external temperature and airflow disturbances, designing a specific resonant cavity structure, adding passive optical fibers to the cavity to replace the spatial optical path, inserting high-dispersion elements into the cavity, etc. Passive control methods can only reduce interference from the external environment, so active control is also required.

[0005] Active control mainly uses external electrical circuits for feedback control. The most typical solution is the jitter-locking method. It is inevitable that the oscillator output signal light has a modulation signal; and in some bands, the peak value of the output power is irregular or flat as the cavity length changes, so the power peak cannot be accurately locked. For example, Patent No. CN111082300B discloses a cavity length locking method and system for a dual-resonance optical parametric oscillator, which uses a wavelength selection element to filter the signal light, thereby solving the problem that the power peak cannot be accurately locked when the structure of the resonance peak is irregular or has a flat top, but its cavity locking point is still at the peak point, and the error signal is locked when the sensitivity of the cavity length is the lowest, which will inevitably provide a greater tolerance for the change of the cavity length; and it needs to introduce additional interference signals, and modulation signals will inevitably appear; Patent No. CN115548852A discloses a pump-enhanced optical parametric oscillator and an active stabilization method and application, which adopts an active control technology of a low-frequency modulation and demodulation method, and can obtain a clearer error signal by increasing the amplitude of the scanning signal at high power, and actively control the stability of the intracavity oscillation pump light power, but it uses the cavity mode signal of the intracavity pump light as the error signal, which is obviously not applicable to ultrafast optical parametric oscillators (generally, there is no cavity mode signal in the cavity of ultrafast optical parametric oscillators). Another unmodulated signal power stabilization scheme uses the second harmonic output power of the OPO as the error signal, locks the cavity length by stabilizing the doubled power, compares the output voltage of the detected doubled output power with the reference voltage to generate an error signal, and feeds back to the PZT in the OPO cavity to tune the cavity length to achieve locking. This method heavily relies on the power peak points of the signal light and the second harmonic not being at the same cavity length point, and has limitations for cavity length locking in any band. Summary of the invention

[0006] In order to overcome the deficiencies of the prior art, the present invention provides an ultrafast optical parametric oscillator cavity length locking device, a laser and a locking method, which utilize a dispersion element and an aperture to select a narrowband spectrum as a cavity locking signal, and utilize the different sensitivities of different wavelengths to the cavity length to lock it at the rising edge or falling edge of the narrowband spectrum power without introducing a disturbance signal, thereby achieving stable operation of the total signal light power at the peak point without a modulation signal.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a cavity length locking device for an ultrafast optical parametric oscillator.

[0009] An ultrafast optical parametric oscillator cavity length locking device comprises: an optical module and a control circuit module;

[0010] The optical module comprises: an optical resonant cavity, a nonlinear crystal, a beam splitter, a dispersive element and an aperture, wherein the optical resonant cavity comprises a plurality of cavity mirrors, the nonlinear crystal is located in the optical resonant cavity, and the optical resonant cavity is used for inputting pump light and multiple reflection enhancement of signal light generated by the nonlinear crystal;

[0011] The part of the signal light after reflection enhancement is guided out of the optical resonant cavity to the beam splitter through a cavity mirror, and the part of the signal light after beam splitting passes through the dispersion element and the aperture in sequence, and the aperture is used to select signal lights of different wavelengths as error light signals by changing the position;

[0012] The control circuit module includes: a first photodetector, a second photodetector and a servo controller, the first photodetector is used to detect the total power of the signal light, the second photodetector is used to convert the error light signal into an error electrical signal, and the servo controller is used to control the total power peak point of the signal light to be at the rising edge or falling edge of the error electrical signal.

[0013] As a further limitation of the first aspect of the present invention, the optical module further includes an ultrafast pump source and a pump focusing mirror, and the pump focusing mirror is used to focus the pump light into the optical resonant cavity.

[0014] As a further limitation of the first aspect of the present invention, the nonlinear crystal is located in a temperature-controlled furnace, and the temperature-controlled furnace is located in the optical resonant cavity.

[0015] As a further limitation of the first aspect of the present invention, the optical resonant cavity comprises: a first cavity mirror, a second cavity mirror, a third cavity mirror and a fourth cavity mirror, the pump light enters the optical resonant cavity from the first lens, and the fourth lens is used to output part of the signal light after reflection enhancement.

[0016] As a further limitation of the first aspect of the present invention, the first cavity mirror and the second cavity mirror are both plano-concave mirrors, with one side without curvature coated with a high-transmittance film for pump light, and the other side with curvature coated with a high-reflection film for signal light and a high-transmittance film for pump light and idler light.

[0017] As a further limitation of the first aspect of the present invention, the third cavity mirror is a plane mirror coated with a high-reflection film for signal light and a high-transmittance film for pump light, and the fourth cavity mirror is a coupling output mirror.

[0018] As a further limitation of the first aspect of the present invention, the pump focusing mirror is a convex lens.

[0019] As a further limitation of the first aspect of the present invention, the control circuit module includes: an amplifier, a low-pass filter, a signal generator, a high-voltage amplifier and a piezoelectric ceramic, and the output signal of the first photodetector enters the first channel of the oscilloscope after being filtered by the low-pass filter;

[0020] The output signal of the second photodetector is selected through an amplifier and a low-pass filter to obtain a required error electrical signal, which is then input into a servo controller. The error signal monitoring port of the servo controller is connected to the second channel of the oscilloscope.

[0021] The signal generator is connected to the servo controller and is used to provide a scanning signal to the servo controller to scan the cavity length of the optical parametric oscillator module. The output port of the servo controller is connected to the input port of the high-voltage amplifier. The output port of the high-voltage amplifier is connected to the piezoelectric ceramic. The servo controller is used to control the piezoelectric ceramic through the error electrical signal amplified by the high-voltage amplifier.

[0022] In a second aspect, the present invention provides a method for locking the cavity length of an ultrafast optical parametric oscillator.

[0023] A method for locking the cavity length of an ultrafast optical parametric oscillator, using the ultrafast optical parametric oscillator cavity length locking device described in the first aspect of the present invention, comprises the following steps:

[0024] The servo controller scans the cavity length according to the received scanning signal, which is amplified by the high-voltage amplifier and then transmitted to the piezoelectric ceramic, and selects the filtered error light signal from the total spectrum of the signal light. The selected error light signal can meet the following control conditions: the peak point of the total power of the signal light detected by the first photodetector is at the rising edge or falling edge of the error electrical signal output by the second photodetector;

[0025] By adjusting the first channel of the oscilloscope, the peak point of the total power of the signal light detected by the first photodetector coincides with the zero position of the second channel, and by adjusting the bias DC on the servo controller, the rising edge or falling edge of the error electrical signal coincides with the peak point of the total power of the signal light;

[0026] The servo controller is adjusted to reduce the amplitude of the scanning signal, and the bias of the scanning voltage of the servo controller is adjusted so that the zero point position does not change, until the scanning signal amplitude is zero, the servo controller is locked, and the cavity length locking process is completed.

[0027] In a third aspect, the present invention provides a laser, comprising the ultrafast optical parametric oscillator cavity length locking device described in the first aspect of the present invention.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention uses a dispersion element and an aperture to select a narrowband spectrum as a cavity locking signal, and uses the different sensitivities of different wavelengths to the cavity length to lock it at the rising or falling edge of the narrowband spectrum power without introducing a disturbance signal, thereby achieving stable operation of the total signal light power at the peak point without a modulation signal.

[0030] 2. The present invention utilizes a wavelength locking device to lock any wavelength within the signal light tuning range, and can enable the ultrafast optical parametric oscillator to maintain wavelength and power stability during long-term operation.

[0031] 3. The second photodetector converts the filtered error light signal into an electrical signal. By comparing the error electrical signal with the total power, as the scanning cavity length changes, the position of the aperture is adjusted to make the total power peak point at the rising edge or falling edge of the error electrical signal, thereby ensuring the locking of the signal light power peak point.

[0032] 4. The present invention is mainly used in ultrafast optical parametric oscillators. The error signal used is the filtered signal of the signal light. A low-pass filter is used to process the narrow-band spectral electrical signal, which not only filters out the high-frequency part (mainly the laser repetition frequency), but also covers the function of the integrator, and can retain the information of the power change with the cavity length without the need for additional mixing and integration.

[0033] 5. The present invention compares the filtered narrowband spectrum power with the total power, finds the peak point of the total power changing with the cavity length by scanning the cavity length, and makes the total power peak point on the rising edge or falling edge of the narrowband spectrum power by adjusting the central wavelength of the filtered narrowband spectrum. Similarly, the narrowband spectrum is used as the error signal, so that the cavity locking point is at the rising edge or falling edge, and is locked at the position where the error signal is most sensitive to the cavity length. The allowable variation of the cavity length is very small, so that the total power output of the OPO signal light is at the peak point. In addition, the present invention does not need to add the error signal to the disturbance signal, thereby avoiding the generation of the modulation signal.

[0034] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0036] Figure 1 A schematic diagram of the ultrafast optical parametric oscillator cavity length locking device provided by the present invention;

[0037] Figure 2 A schematic diagram of the signal light spectrum output by the optical parametric oscillator and the error light signal after filtering in the experiment provided by the present invention;

[0038] Figure 3 A schematic diagram showing how the total power of the signal light and the error light signal after filtering vary with the cavity length in the experiment provided by the present invention;

[0039] Figure 4A schematic diagram of the long-term operation of the signal light power and spectrum without adding a cavity length locking device provided by the present invention;

[0040] Figure 5 It is a schematic diagram of the long-term operation of the signal light power and spectrum after adding the cavity length locking device provided by the present invention.

[0041] Among them, 101, ultrafast pump source; 102, pump focusing mirror; 201, first cavity mirror; 202, second cavity mirror; 203, third cavity mirror; 204, fourth cavity mirror; 205, beam splitter; 301, nonlinear crystal; 401, temperature controlled furnace; 501, dispersion element; 502, aperture; 601, first photodetector; 602, second photodetector; 602, second photodetector; 603, amplifier; 604, low-pass filter; 605, servo controller; 606, signal generator; 607, high-voltage amplifier; 608, piezoelectric ceramics. DETAILED DESCRIPTION

[0042] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0043] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0044] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including", "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0045] In this implementation, a cavity length locking device for an ultrafast optical parametric oscillator is proposed, which realizes the long-term stable operation of the power and wavelength of the ultrafast optical parametric oscillator. The cavity length can be locked in any band of the optical parametric oscillator output, and the different sensitivities of different wavelengths to the cavity length can be utilized to lock the peak point of the signal light power without the output of a modulated signal.

[0046] First, some nouns or terms that appear in the description of the embodiments of the present application are subject to the following explanations:

[0047] An optical parametric oscillator (OPO) is a parametric oscillator that oscillates at optical frequencies. It uses nonlinear optical effects to generate frequency-tunable coherent light in optical crystals. The working principle of OPO is based on nonlinear optical effects and three-wave mixing processes. When the input pump light interacts with the signal light in the nonlinear crystal, a frequency-tunable optical parametric wave (idler light) is generated; in this process, energy is transferred from the pump light to the optical parametric wave, realizing optical parametric amplification and frequency conversion. Optical parametric oscillators can be used in the following technical fields:

[0048] (1) Spectroscopy and infrared spectroscopy measurement. OPO can generate laser light with a wide range of continuously adjustable wavelengths, which is particularly suitable for high-resolution spectroscopy research;

[0049] (2) LiDAR and spectral sensing: The stable coherent light source provided by OPO can be used to achieve high-resolution and high-sensitivity distance and speed measurement;

[0050] (3) Optical communications and quantum information processing: OPOs can be used to generate entangled photon pairs to realize applications such as quantum key distribution and quantum teleportation;

[0051] (4) Biomedicine and materials science: OPO can be used to generate tunable deep ultraviolet lasers to achieve non-destructive detection and analysis of biological samples, as well as high-precision processing and micro-nano manufacturing of materials.

[0052] In this implementation, the optical parametric oscillator cavity length locking device includes: an optical module and a control circuit module, wherein the optical module is used to perform an optical parametric process to output ultrashort pulses and provide an error optical signal for the control circuit.

[0053] More specifically, Figure 1 As shown, the optical module includes an ultrafast pump source 101, a pump focusing mirror 102, a first cavity mirror 201, a second cavity mirror 202, a third cavity mirror 203, a fourth cavity mirror 204, a beam splitter 205, a nonlinear crystal 301, a temperature-controlled furnace 401, a dispersion element 501 and an aperture 502. The ultrafast pump light is sequentially focused to the center of the nonlinear crystal 301 through the pump focusing mirror. The first cavity mirror 201, the second cavity mirror 202, the third cavity mirror 203 and the fourth cavity mirror 204 form a resonant cavity of an optical parametric oscillator. The temperature-controlled furnace 401 is used to control the temperature of the nonlinear crystal 301. Part of the signal light enhanced by the resonant cavity reflection is output through the fourth cavity mirror 204, and then split by the beam splitter 205. Part of the signal light is directly output, and the other part of the signal light is filtered out of a narrow-band spectrum as an error light signal through the dispersion element 501 and the aperture 502.

[0054] In this implementation, the central wavelength of the ultrafast pump source 101 is 1040 nm or 520 nm, the generated signal light wavelength is 1400 nm-1900 nm or 650 nm-980 μm, and the corresponding idler light wavelength is 2298 nm-4044 nm or 1108-2600 nm.

[0055] In this implementation, the pump focusing mirror 102 is a convex lens with a focal length of 75 mm or 100 mm, which is used for cavity membrane matching of the resonant cavity.

[0056] In the present implementation, the first cavity mirror 201 and the second cavity mirror 202 are plano-concave mirrors, and the radius of curvature is 100 mm or 150 mm. The side without curvature is coated with a high-transmittance film for pump light, and the side with curvature is coated with a high-reflection film for signal light and a high-transmittance film for pump light and idler light; the third cavity mirror 203 is a plane mirror, coated with a high-reflection film for signal light and a high-transmittance film for pump light; the fourth cavity mirror 204 is a coupling output mirror, and the reflectivity of the signal light is between 85% and 98%, and the reflectivity is preferably set to 92%.

[0057] In this implementation, the dispersion element 501 and the aperture 502 filter the wide spectrum signal light. By controlling the position of the aperture 502, different wavelengths can be selected as error light signals. The dispersion element 501 can be a grating, a prism, a filter, etc.

[0058] In this implementation, the control circuit module provides active control for the entire optical system, converts the error optical signal into an electrical signal, and locks the optical parametric oscillator at the peak power, so that its power and wavelength remain stable for a long time.

[0059] Specifically, the control circuit module includes: a first photodetector 601 , a second photodetector 602 , an amplifier 603 , a low-pass filter 604 , a servo controller 605 , a signal generator 606 , a high-voltage amplifier 607 and a piezoelectric ceramic 608 .

[0060] In this implementation, the first photodetector 601 detects the change of the total power of the signal light with the cavity length to determine whether the signal light is at the peak power; the second photodetector 602 converts the filtered error light signal into an electrical signal, and compares the error electrical signal with the total power. As the scanning cavity length changes, the position of the aperture 502 is adjusted to make the total power peak point at the rising edge or falling edge of the error electrical signal.

[0061] In this implementation, the low-pass filter 604 filters the high-frequency pulse electrical signal detected by the photodetectors 601-602, which not only filters out the useless high-frequency part (laser repetition frequency), but also includes the function of an integrator, and can retain the error optical signal power information.

[0062] The first photodetector 601 is used to detect the total power change of the signal light and input it into the first channel of the oscilloscope. The second photodetector 602 is used to convert the filtered narrowband spectral power into an electrical signal. The required error electrical signal is selected through the amplifier 603 and the low-pass filter 604 and enters the servo controller 605. The error signal monitoring port of the servo controller 605 is connected to the second channel of the oscilloscope. The signal generator 606 provides a scanning signal for the servo controller 605 to scan the cavity length of the optical parametric oscillator module. The output port of the servo controller 605 is connected to the input port of the high-voltage amplifier 607. The error electrical signal amplified by the high-voltage amplifier 607 is used to control the piezoelectric ceramic 608.

[0063] Based on the above-mentioned ultrafast optical parametric oscillator cavity length locking device, this implementation provides a specific ultrafast optical parametric oscillator cavity length locking method, including the following process:

[0064] S1: The signal generator 606 outputs a Hz-level low-frequency triangular wave reference signal to the servo controller 605 as a scanning signal, which is amplified by the high-voltage amplifier 607 and then transmitted to the piezoelectric ceramic 608 to scan the cavity length; in the total spectrum of the signal light (i.e. Figure 2 a) Select the appropriate filtered error light signal (i.e. Figure 2 b) in the formula to satisfy Figure 3 The schematic diagram shown is that the total power of the signal light (first photodetector) and the power of the filtered error light signal (second photodetector) vary with the cavity length, that is, the peak point of the total power is at the rising edge or falling edge of the error electrical signal.

[0065] S2: Adjust the first channel of the oscilloscope so that the peak point of the total power of the signal light detected by the first photodetector 601 coincides with the zero position of the second channel. At the same time, by adjusting the bias DC on the servo controller 605 (without changing the cavity length), the rising edge or falling edge of the error electrical signal coincides with the peak point of the total power of the signal light.

[0066] S3: Adjust the servo controller 605 to reduce the amplitude of the scanning signal. While observing the amplitude change, adjust the bias of the scanning voltage of the servo controller 605 (change the cavity length) to ensure that the zero point position does not change, until the scanning signal amplitude is zero, turn on the servo controller 605 lock button to complete the cavity length locking.

[0067] In order to conduct comparative analysis, the present implementation provides a device that does not include a control circuit module, that is, only includes the above-mentioned optical module, and tests the output results to compare the influence of the control circuit module on the power and spectrum during the long-term operation of the optical parametric oscillator.

[0068] When the control circuit module is not added, the central wavelength of the optical parametric oscillator is 740nm, and the spectrum is observed continuously for 18 minutes. The corresponding spectrum is as follows Figure 4 As shown in a in the figure, the spectrum of the signal light power is continuously observed for 18 minutes, and the corresponding power is as follows Figure 4 As shown in b in the figure, it can be seen from the results that the spectrum stability is poor and the power stability RMS is 4%.

[0069] When the control circuit module is added, the central wavelength of the optical parametric oscillator is 740nm. The spectrum is observed continuously for 1 hour. The corresponding spectrum is as follows Figure 5 As shown in a; at the same time, the optical power of the signal light is continuously observed for 1 hour, and the corresponding power is as follows Figure 5 As shown in b in the figure, the spectrum stability is better than when the control circuit module is not added, and the power stability RMS is 1.6%.

[0070] The above diagram only lists one signal light wavelength (740), but is not limited thereto and is applicable to the entire tuning band. Those skilled in the art can select it according to specific working conditions, which will not be described in detail here.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An ultrafast optical parametric oscillator cavity length locking device, characterized in that: include: Optical module and control circuit module; The optical module comprises: an optical resonant cavity, a nonlinear crystal, a beam splitter, a dispersive element and an aperture, wherein the optical resonant cavity comprises a plurality of cavity mirrors, the nonlinear crystal is located in the optical resonant cavity, and the optical resonant cavity is used for inputting pump light and multiple reflection enhancement of signal light generated by the nonlinear crystal; The part of the signal light after reflection enhancement is guided out of the optical resonant cavity to the beam splitter through a cavity mirror, and the part of the signal light after beam splitting passes through the dispersion element and the aperture in sequence, and the aperture is used to select signal lights of different wavelengths as error light signals by changing the position; The control circuit module comprises: a first photodetector, a second photodetector and a servo controller, wherein the first photodetector is used to detect the total power of the signal light, the second photodetector is used to convert the error light signal into an error electrical signal, and the servo controller is used to control the total power peak point of the signal light to be at the rising edge or the falling edge of the error electrical signal; The control circuit module includes: an amplifier, a low-pass filter, a signal generator, a high-voltage amplifier and piezoelectric ceramics. The output signal of the first photodetector enters the first channel of the oscilloscope after being filtered by the low-pass filter; The output signal of the second photodetector is selected through an amplifier and a low-pass filter to obtain a required error electrical signal, which is then input into a servo controller. The error signal monitoring port of the servo controller is connected to the second channel of the oscilloscope. The signal generator is connected to the servo controller, and is used to provide a scanning signal to the servo controller to scan the cavity length of the optical parametric oscillator module. The output port of the servo controller is connected to the input port of the high-voltage amplifier, and the output port of the high-voltage amplifier is connected to the piezoelectric ceramic. The servo controller is used to control the piezoelectric ceramic through the error electrical signal amplified by the high-voltage amplifier. Adjust the servo controller to reduce the amplitude of the scanning signal. While observing the amplitude change, adjust the bias of the servo controller scanning voltage, that is, change the cavity length to ensure that the zero point position does not change, until the scanning signal amplitude is zero, turn on the servo controller lock button, and complete the cavity length locking.

2. The ultrafast optical parametric oscillator cavity length locking device according to claim 1, characterized in that: The optical module also includes an ultrafast pump source and a pump focusing mirror, and the pump focusing mirror is used to focus the pump light into the optical resonant cavity.

3. The ultrafast optical parametric oscillator cavity length locking device according to claim 1, characterized in that: The nonlinear crystal is located in a temperature-controlled furnace, and the temperature-controlled furnace is located in the optical resonant cavity.

4. The ultrafast optical parametric oscillator cavity length locking device according to claim 1, characterized in that: The optical resonant cavity comprises: a first cavity mirror, a second cavity mirror, a third cavity mirror and a fourth cavity mirror. The pump light enters the optical resonant cavity from the first lens, and the fourth lens is used to output part of the signal light after reflection enhancement.

5. The ultrafast optical parametric oscillator cavity length locking device according to claim 4, characterized in that: The first cavity mirror and the second cavity mirror are both plano-concave mirrors, with a non-curved side coated with a high-transmittance film for pump light, and a curved side coated with a high-reflection film for signal light and a high-transmittance film for pump light and idler light.

6. The ultrafast optical parametric oscillator cavity length locking device according to claim 4, characterized in that: The third cavity mirror is a plane mirror coated with a high-reflection film for signal light and a high-transmittance film for pump light, and the fourth cavity mirror is a coupling output mirror.

7. The ultrafast optical parametric oscillator cavity length locking device according to claim 1, characterized in that: The pump focusing mirror is a convex lens.

8. A method for locking the cavity length of an optical parametric oscillator, characterized in that: Using the ultrafast optical parametric oscillator cavity length locking device according to any one of claims 1 to 7, The process includes: The servo controller scans the cavity length according to the received scanning signal, which is amplified by the high-voltage amplifier and then transmitted to the piezoelectric ceramic, and selects the filtered error light signal from the total spectrum of the signal light. The selected error light signal can meet the following control conditions: the peak point of the total power of the signal light detected by the first photodetector is at the rising edge or falling edge of the error electrical signal output by the second photodetector; By adjusting the first channel of the oscilloscope, the peak point of the total power of the signal light detected by the first photodetector coincides with the zero position of the second channel, and by adjusting the bias DC on the servo controller, the rising edge or falling edge of the error electrical signal coincides with the peak point of the total power of the signal light; The servo controller is adjusted to reduce the amplitude of the scanning signal, and the bias of the scanning voltage of the servo controller is adjusted so that the zero point position does not change, until the scanning signal amplitude is zero, the servo controller is locked, and the cavity length locking process is completed.

9. A laser, characterized in that: The invention comprises the ultrafast optical parametric oscillator cavity length locking device as described in any one of claims 1 to 7.

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