Purple picosecond laser pulse time domain diagnosis system of free electron laser device

Abstract

The utility model provides a purple picosecond laser pulse time domain diagnosis system of a free electron laser device. The purple picosecond laser pulse time domain diagnosis system comprises an oscillator, an amplifier, a quadruplicated frequency module, an ultraviolet laser pulse time domain shaping module and a diagnosis system which are connected in sequence, the diagnosis system comprises a half-wave plate, a polarization beam splitter, a high reflective mirror, a lens, a signal indication light plug-in, a beam combiner, a BBO crystal, a dispersion prism, a band-pass filter and a photomultiplier, wherein the photomultiplier is connected with an oscilloscope. The function of the signal indication light plug-in is to output 360 nm signal light, and the signal light and light to be measured are collinearly output in a measurement light path so as to determine the position of the signal light generated in the actual measurement process; then a photomultiplier is installed at the position to detect signal light, then a signal indication light plug-in is moved out of a diagnosis light path, and time domain diagnosis of ultraviolet pulses is carried out; signal light is accurately and efficiently collected through the system, so that the problem that the installation position of the photoelectric detector cannot be determined due to too small signal light energy is solved.

Description

Technical Field

[0001] The utility model relates to an ultraviolet picosecond laser pulse time domain diagnosis system of a free electron laser device. Background Art

[0002] Free electron laser is the brightest X-ray coherent light source in the world. It is currently being applied to the most cutting-edge research in many fields, such as pump-probe ultrafast chemistry, single particle imaging, nonlinear optics, etc. At present, free electron laser devices are developing towards continuous wave high repetition frequency (MHz), ultrashort wavelength (<1nm), and high pulse energy. One of the key links is to further reduce the emissivity of the electron beam and improve the brightness and stability of the electron beam. The function of the driving laser is to act on the photocathode electron gun to generate an electron beam. Longitudinal shaping of the driving laser is one of the most effective and promising ways to obtain a low-emissivity, high-brightness electron beam. Therefore, after completing the shaping of the driving laser, time domain diagnosis of the driving laser is a very important link.

[0003] In the field of ultrafast optics, second harmonic autocorrelation methods are commonly used to diagnose ultrafast laser pulses. However, such methods are not applicable to the ultraviolet band because it is impossible to obtain crystals with second harmonic phase matching conditions in the ultraviolet band.

[0004] In the ultraviolet band, the optical cross-correlation method is often used to diagnose the time domain characteristics of ultraviolet pulses. For ultraviolet laser pulses with a wavelength of 210nm, researchers have used non-collinear cross-correlation scanning to measure the time domain distribution of laser pulses [Jing Yang et al., Pulse broadening of deep ultraviolet femtosecond laserfrom second harmonic generation in KBe2BO3F2, Optics Communications, 288(2013)114-117]. Patent CN106855437A also uses this non-collinear measurement method to measure the pulse width of 266nm ultraviolet laser. This non-collinear cross-correlation scanning method requires that the input probe light and the light to be measured have a single pulse energy of the order of 10 microjoules in order to determine the generation position of the signal light and then determine the position of the photodetector. For probe light with a single pulse energy of about several nJ, the generated signal light is very weak (in the order of picojoules), and the above non-collinear measurement method is difficult to determine the position of the signal light, making the measurement process very difficult.

[0005] In the field of free electron lasers, the current patent CN202020121020.5 designs a 266nm ultraviolet femtosecond seed laser pulse width measurement device, which adopts a collinear measurement method. In this method, the wavelength of the probe light is 800nm, the wavelength of the ultraviolet light to be measured is 266nm, and the wavelength of the generated signal light is 400nm. For this collinear measurement method, the 800nm ​​probe light and the 400nm signal light have a direct frequency doubling relationship, so the position of the signal light can be easily found through BBO frequency doubling. For the conditions where the wavelength of the probe light is 1030nm and the wavelength of the light to be measured is 257nm, there is no frequency doubling relationship between the signal light and the probe light or the light to be measured, so the direct application of this method cannot determine the position of the signal light, and thus cannot be measured.

[0006] Compared with the experimental conditions in the current public literature, it is necessary to design a new, reasonable and efficient ultraviolet pulse time-domain diagnostic system for the test conditions that neither have high pulse energy to directly observe the signal light position nor can find the signal light through convenient difference and frequency doubling design (such as the probe light wavelength is 1030nm and the measured light wavelength is 257nm). Utility Model Content

[0007] The utility model aims to provide a time domain diagnosis system for ultraviolet picosecond laser pulses of a free electron laser device, so as to realize online real-time pulse width diagnosis of ultraviolet laser pulses and improve the time resolution and accuracy of the measurement results.

[0008] In order to achieve the above-mentioned purpose, the utility model provides an ultraviolet picosecond laser pulse time domain diagnostic system of a free electron laser device, comprising an oscillator, an amplifier, a quadruple frequency module, an ultraviolet laser pulse time domain shaping module and a diagnostic system connected in sequence; the oscillator is configured to output probe light and input light of the amplifier, the quadruple frequency module is configured to convert the output light of the amplifier into an ultraviolet driving laser pulse by frequency doubling, the ultraviolet laser pulse time domain shaping module stretches the ultraviolet driving laser pulse to a picosecond pulse width required for driving the laser, and inputs it to the diagnostic system as light to be measured; the diagnostic system comprises a half-wave plate, a polarization beam splitter, a first infrared plane high reflection mirror, a second infrared plane high reflection mirror, a third infrared plane high reflection mirror, and a fourth infrared plane arranged in sequence along the optical path of the probe light. A high-reflection mirror, a fifth infrared plane high-reflection mirror and a sixth infrared plane high-reflection mirror, an infrared lens, a signal indicator light plug-in that can be moved in and out of the optical path, a beam combiner, a BBO crystal, a dispersion prism, a bandpass filter and a photomultiplier tube, wherein the photomultiplier tube is connected to an oscilloscope, an optical path of the light to be measured is provided between the beam combiner and the output end of the ultraviolet laser pulse time domain shaping module, and an ultraviolet lens is provided; when the probe light and the light to be measured meet the time and space overlap in the BBO crystal, signal light is generated, and the dispersion prism and the bandpass filter are used to separate the signal light and transmit it to the photomultiplier tube; when the signal indicator light plug-in is moved into the optical path, the signal indicator light and the light to be measured are collinear at the downstream of the beam combiner, and the photomultiplier tube is arranged at the spot position of the signal indicator light.

[0009] The wavelength of the light to be measured is 257nm, and the wavelength of the probe light is 1030nm, so that when the probe light and the light to be measured meet the time and space overlap in the BBO crystal, a signal light with a wavelength of 342nm is generated; the signal indicator light plug-in is an optical fiber and is coupled with an external 360nm light source to collimate and output a signal indicator light with a wavelength of 360nm.

[0010] The thickness of the BBO crystal is at most 0.1 mm, and the cutting angle is =42.2°.

[0011] The polarization state of the probe light is perpendicular to the polarization state of the light to be measured, the probe light is o light, and the light to be measured is e light; the half-wave plate and the polarization beam splitter are used to determine the polarization state of the probe light, thereby ensuring that the polarization state of the probe light is adjusted to horizontal polarization.

[0012] The first infrared plane high reflective mirror and the second infrared plane high reflective mirror are directly opposite to each other, and the incident angles of the light to be measured on the first infrared plane high reflective mirror and the second infrared plane high reflective mirror are both set to 10°, so that the combination of the first infrared plane high reflective mirror and the second infrared plane high reflective mirror is used to adjust the optical path difference of the probe light relative to the light to be measured, and the adjustment range of the optical path difference between the first infrared plane high reflective mirror and the second infrared plane high reflective mirror is 1ns to 15ns.

[0013] The fifth infrared plane high-reflection mirror and the sixth infrared plane high-reflection mirror are installed on the same electric translation stage, so as to achieve the temporal overlap of the light to be measured and the probe light by controlling the movement of the electric translation stage; the electric translation stage is also configured to enable the oscilloscope to collect the distribution curve between the intensity of the signal light and the position of the high-precision delay line as the intensity distribution curve of the difference frequency signal light during scanning, and the half-height full width of the intensity distribution curve of the difference frequency signal light is The pulse width of the light to be measured The relationship is:

[0014] ,

[0015] in, is the full width at half maximum of the intensity distribution curve of the difference frequency signal light, is the pulse width of the probe light.

[0016] The scanning range of the electric translation stage is 0 mm-400 mm, and the minimum displacement increment of the scanning is 30 nm.

[0017] The signal indicator light plug-in is installed on a quickly disassembled four-dimensional optical adjustment frame, and the four-dimensional optical adjustment frame is used to realize the colinearity of the signal indicator light and the light to be measured.

[0018] The BBO crystal is mounted on a crystal optical adjustment frame.

[0019] The pulse width of the probe light is 50-200 femtoseconds, the average power is 10-150 milliwatts, the repetition frequency is 0.1-100 MHz, and the single pulse energy is 1-10 nanojoules.

[0020] The ultraviolet picosecond laser pulse time domain diagnostic system of the free electron laser device of the utility model applies a light source close to the signal light wavelength of 342nm externally, and the wavelength of the output light is 360nm. The signal indicator light plug-in is obtained by coupling the light source to the optical fiber coupler, and is outputted in the measurement optical path in a colinear manner with the light to be measured to determine the position of the signal light generated during the actual measurement process, and then a photomultiplier tube is installed at this position to detect the signal light. After the signal indicator light plug-in is moved out of the diagnostic optical path, the ultraviolet pulse time domain diagnosis is performed, thereby overcoming the problem that the probe light energy is too small to determine the position of the signal light. Therefore, for test conditions that can neither have high pulse energy to directly observe the signal light position nor find the signal light through convenient difference and frequency doubling design, it is still possible to achieve online real-time pulse width diagnosis of ultraviolet laser pulses and improve the time resolution and accuracy of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1The utility model is a schematic structural diagram of an ultraviolet picosecond laser pulse time domain diagnostic system of a free electron laser device.

[0022] Figure 2 This is a diagram of actual measurement results of a 257nm ultraviolet driving laser pulse for diagnosing a free electron laser device obtained by the ultraviolet picosecond laser pulse time domain diagnostic system of the free electron laser device of the utility model. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0024] When the probe light and the light to be measured pass through the BBO crystal, and the probe light and the light to be measured meet the time and space coincidence and phase matching conditions in the BBO crystal, signal light can be generated.

[0025] Among them, the wavelengths of the probe light and the light to be measured can only generate signal light of the corresponding wavelength when the following conditions are met:

[0026] ,

[0027] in, is the wavelength of the ultraviolet light to be measured, which is approximately 257nm; is the wavelength of the probe light, which is 1030nm, is the wavelength of the signal light, which is 342nm.

[0028] Therefore, when the above conditions are met, it cannot be guaranteed that the wavelength of the probe light is an integer multiple of the wavelength of the signal light, and then to find the signal light through simple difference and frequency doubling, it is necessary to design a UV picosecond laser pulse time domain diagnostic system for the free electron laser device. In addition, it cannot be guaranteed that the signal light can be directly observed.

[0029] like Figure 1 The figure shows an ultraviolet picosecond laser pulse time domain diagnostic system of a free electron laser device according to an embodiment of the utility model, which includes an oscillator 1, an amplifier 2, a quadruple frequency module 3, an ultraviolet laser pulse time domain shaping module 4 and a diagnostic system 5 connected in sequence.

[0030] The oscillator 1 is configured to output the probe light and the input light of the amplifier 2. The probe light is output from the oscillator 1 to the half-wave plate P1 of the diagnosis system 5.

[0031] In this embodiment, the probe light has a central wavelength of 1030 nm, a bandwidth of 14 nm, a pulse width of 100 fs, an average power of about 121 mW, a frequency of 36 MHz, and a single pulse energy of 2.7 nJ. In other embodiments, the probe light has a pulse width of 50-200 femtoseconds, an average power of 10-150 mW, a repetition frequency of 0.1-100 MHz, and a single pulse energy of 1-10 nanojoules.

[0032] The amplifier 2 is configured to amplify the energy of the input light of the amplifier. The output light of the amplifier 2 is infrared light with an output repetition frequency of 1 Hz-1 MHz for optical pulses, a pulse width of 100-1000 femtoseconds, an average power of 10-100 watts, and a wavelength of about 1030 nm.

[0033] The quadruple frequency module 3 is configured to convert the output light of the amplifier into a 257nm ultraviolet driven laser pulse by frequency doubling, with a bandwidth of 0.51nm and a pulse width of 200-2000 femtoseconds.

[0034] The ultraviolet laser pulse time domain shaping module 4 stretches the 200-2000 femtosecond ultraviolet driving laser pulse to the picosecond pulse width required for driving the laser, and inputs it to the diagnostic system 5 as the light to be measured, wherein the single pulse energy of the light to be measured is less than 0.4uJ.

[0035] The diagnostic system 5 includes a half-wave plate P1, a polarization beam splitter P2, a first infrared plane high-reflection mirror M1, a second infrared plane high-reflection mirror M2, a third infrared plane high-reflection mirror M3, a fourth infrared plane high-reflection mirror M4, a fifth infrared plane high-reflection mirror M5 and a sixth infrared plane high-reflection mirror M6, an infrared lens F1, a signal indicator light plug-in T0 that can be moved in and out of the optical path, a beam combiner M7, a BBO crystal T1, a dispersion prism T2, a bandpass filter T3, a photomultiplier tube T4, which are arranged in sequence along the optical path of the probe light, and are connected to an oscilloscope (not shown in the figure). There is an optical path of the light to be measured between the beam combiner M7 and the output end of the ultraviolet laser pulse time domain shaping module 4 and is provided with an ultraviolet lens F2.

[0036] Among them, the first infrared plane high reflective mirror M1, the second infrared plane high reflective mirror M2, the third infrared plane high reflective mirror M3, the fourth infrared plane high reflective mirror M4, the fifth infrared plane high reflective mirror M5 and the sixth infrared plane high reflective mirror M6 are all infrared plane high reflective mirrors with low group delay dispersion.

[0037] The probe light and the light to be measured generate signal light when the phase matching condition is met in the BBO crystal T1. The dispersion prism T2 and the bandpass filter T3 are used to separate the signal light and transmit it to the photomultiplier tube T4. When the signal indicator light plug-in T0 is moved into the optical path, the signal indicator light and the light to be measured are collinear downstream of the beam combiner M7. The photomultiplier tube T4 is arranged at the spot position of the signal indicator light.

[0038] In this embodiment, the wavelength of the light to be measured is 257 nm, and the wavelength of the probe light is 1030 nm, so that the probe light and the light to be measured meet the temporal and spatial overlap in the BBO crystal T1 to generate signal light with a wavelength of 342 nm.

[0039] Because when the difference frequency signal is generated, the polarization state of the probe light (o light) needs to be perpendicular to the polarization state of the light to be measured (e light), only when the perpendicular condition is met, they will generate a 342nm signal light when passing through the BBO crystal. Therefore, in this embodiment, before measurement, the polarization states of the probe light and the light to be measured are checked using a half-wave plate P1 and a polarization beam splitter P2 to ensure that the polarization state of the probe light is adjusted to horizontal polarization (while the polarization state of the light to be measured is vertical polarization). Among them, the half-wave plate P1 and the polarization beam splitter P2 are used to judge the 1030nm probe light, and the way in which the half-wave plate P1 and the polarization beam splitter P2 judge the polarization state of the probe light includes: rotating the half-wave plate P1 so that the light output by the polarization beam splitter P2 reaches the strongest. If you want to judge the wavelength of the light to be measured with a wavelength of 257nm, you can also use a 257nm half-wave plate and a 257nm polarization beam splitter to judge the polarization state of the 257nm ultraviolet light.

[0040] The first infrared plane high reflective mirror M1 and the second infrared plane high reflective mirror M2 face each other, and the incident angles of the light to be measured on the first infrared plane high reflective mirror M1 and the second infrared plane high reflective mirror M2 are set to be less than 10°, so that the combination of the first and second infrared plane high reflective mirrors is used to adjust the optical path difference of the probe light relative to the light to be measured, and the adjustment range of the optical path difference between the first infrared plane high reflective mirror and the second infrared plane high reflective mirror is 1ns to 15ns. This compact and multiple light returns are used to quickly and roughly make up for the optical path difference between the probe light and the light to be measured.

[0041] The fifth infrared plane high reflective mirror M5 and the sixth infrared plane high reflective mirror M6 are installed on the same high-precision electric translation stage 6. The movement of the electric translation stage 6 is controlled to achieve precise temporal coincidence of the light to be measured and the probe light, so that the two generate difference frequency signal light after passing through the BBO crystal.

[0042] In addition, the electric translation stage 6 is also configured to enable the oscilloscope to collect a distribution curve between the intensity of the difference frequency signal light and the position of the high-precision delay line during scanning as an intensity distribution curve of the difference frequency signal light, and the half-maximum full width of the intensity distribution curve of the difference frequency signal light is related to the pulse width of the light to be measured.

[0043] Specifically, the full width at half maximum of the intensity distribution curve of the difference frequency signal light is The pulse width of the light to be measured The relationship is:

[0044] ,

[0045] in, is the full width at half maximum of the intensity distribution curve of the difference frequency signal light, is the pulse width of the probe light.

[0046] Therefore, after calculating the half-height full width of the distribution curve, the pulse width of the light to be measured (ie, the ultraviolet seed laser to be measured) can be obtained through simple conversion.

[0047] The scanning range of the electric translation stage 6 is in the range of 0-400 mm, and the minimum displacement increment of the scanning is 30 nm, so that scanning of the order of 1 ns can be achieved. In this embodiment, the scanning range of the electric translation stage 6 is greater than 200 mm, the repeatability is ±0.05 μm, the accuracy is ±1.7 μm, and the bidirectional repeatability is ±0.25 μm. Therefore, the time resolution of the scanning of the electric translation stage 6 is estimated to be 1.7×2 / 0.3 fs, that is, the time resolution of the scanning is better than 13 fs, the difference frequency signal is easy to find, and remote automatic scanning can be achieved, and the light to be measured with a wavelength of 257 nm and a pulse width of 100 femtoseconds to 100 picoseconds can be measured.

[0048] The signal indicator light plug-in T0 is an optical fiber and is coupled with an external 360nm light source to collimate and output a signal indicator light with a wavelength of 360nm. The signal indicator light plug-in T0 can be placed between the beam splitter and the infrared lens in a quick-disassembled manner to achieve co-linearity with the light to be measured. This co-linear setting can directly and efficiently determine the position of the 342nm signal light, and adjust the position of the photomultiplier tube T4 according to the position of the signal light. In addition, the pulse width of the probe light of the ultraviolet picosecond laser pulse time domain diagnostic system of the free electron laser device of the utility model is about 100fs, and under the condition of low energy of the probe light, a high-sensitivity photomultiplier tube T4 is used as a detector to improve the sensitivity of the measurement system.

[0049] The signal indicator light plug-in T0 is located between the beam combiner M7 and the infrared lens F1. The signal indicator light plug-in T0 is installed on a four-dimensional optical adjustment frame that can be fine-tuned in four directions. The adjustable directions are horizontal, vertical, rotation in the vertical plane, and rotation in the horizontal plane. The four-dimensional optical adjustment frame is used to achieve the collinearity of the signal indicator light and the light to be measured, thereby indicating the position of the difference frequency signal.

[0050] The beam combiner M7 is located at the intersection of the optical path of the light to be measured and the optical path of the probe light. In this embodiment, the angle between the beam combiner M7 and the optical path of the light to be measured is 45°, and the angle between the beam combiner M7 and the probe light is 0°. The beam combiner M7 is configured to reflect the light to be measured, the probe light output by the oscillator, and the signal indicator light.

[0051] In other embodiments, several more red / ultraviolet plane high-reflection mirrors may be added according to the space and the need to adjust the optical path and collimate the optical path. For example, two or more infrared plane high-reflection mirrors may be provided between the high-reflection mirror M6 and the beam combiner M7 to ensure that the beam combiner is located at the intersection of the optical path of the light to be measured and the optical path of the probe light.

[0052] Thus, the light to be measured output by the ultraviolet laser pulse time domain shaping module 4 and the probe light output by the oscillator 1 are irradiated on the center of the BBO crystal T1 after passing through the beam combiner M7, and a difference frequency signal light with a wavelength of 342nm is generated under the condition of phase matching. After passing through the dispersion prism T2, the three wavelengths of light, 1030nm, 342nm, and 257nm, are separated in space, and after the difference frequency signal light passes through the bandpass filter T3, the noise light of other bands is filtered out, and only the light of 342nm is allowed to pass, thereby reducing the influence of the probe light, the light to be measured and the ambient light on the measurement accuracy. The intensity of the signal light irradiated on the photomultiplier tube T4 is converted into a corresponding voltage signal, and an oscilloscope is used to collect it.

[0053] Among them, in order to improve the time resolution and accuracy of the measurement system, the thickness of the BBO crystal T1 is at most 0.1mm, and the cutting angle is =42.2°. Under this angle, when the probe light with a wavelength of about 1030nm and the light to be measured with a wavelength of 257nm pass through this BBO crystal T1 (i.e., β-BBO crystal), a difference frequency signal light with a wavelength of 342nm can be generated, and the β-BBO crystal with a thickness of ≤0.1mm can reduce the influence of group velocity mismatch on the broadening of the cross-correlation signal, thereby improving the accuracy of the measurement device. The BBO crystal T1 is mounted on a crystal optical adjustment frame; during the measurement process, by adjusting the knob on the crystal optical adjustment frame, the angle of the BBO crystal T1 mounted on the optical adjustment frame is fine-tuned to obtain the best BBO crystal posture, and the strongest signal light is obtained by fine-tuning the phase matching angle of the BBO crystal T1.

[0054] The ultraviolet picosecond laser pulse time domain diagnosis system based on the free electron laser device described above, the ultraviolet picosecond laser pulse time domain diagnosis method implemented includes the following steps:

[0055] Step S1: lead out the probe light from the oscillator 1 and lead out the light to be measured from the ultraviolet laser pulse time domain shaping module 4; install the first infrared plane high reflective mirror M1 to the sixth infrared plane high reflective mirror M6 and the beam combining mirror M7 in sequence along the direction of the optical path of the light to be measured; set a light intensity detector at the intersection of the light to be measured and the probe light to perform a preliminary measurement of the optical path difference between the probe light and the light to be measured (i.e., check the time difference between the probe light and the light to be measured detected by the light intensity detector through an oscilloscope) and adjust the spacing between the first infrared plane high reflective mirror M1 and the second infrared plane high reflective mirror M2 according to the measurement result to achieve coarse synchronization of the light to be measured and the probe light.

[0056] Step S2: Install BBO crystal T1, dispersion prism T2, bandpass filter T3 and photomultiplier tube T4 in sequence along the optical path of the light to be measured, and connect the photomultiplier tube T4 to the oscilloscope; at this time, move the signal indicator light plug-in T0 into the optical path, and adjust the four-dimensional optical adjustment frame to make the signal indicator light and the light to be measured collinear downstream of the beam combiner M7; then, directly observe the position of the light spot of the signal indicator light after passing through the dispersion prism and adjust the photomultiplier tube T4 to this position, so as to realize the positioning of the signal light. Here, since the light intensity of the signal indicator light with a wavelength of 360nm is relatively strong, it can be directly observed through white paper.

[0057] Among them, the four-dimensional optical adjustment frame is adjusted to make the signal indicator light and the signal to be measured collinear after the beam combiner. Based on the principle of two points determining a straight line, the light to be measured first passes through two aperture holes, and then the indicator signal light is adjusted so that the indicator signal light also passes through the same two aperture holes.

[0058] It should be noted that although the ultraviolet picosecond laser pulse time domain diagnostic system of the free electron laser device of the utility model has a dispersion prism T2, since the wavelengths of the signal light of 342nm and the indicator signal light of 360nm are very close, the position where the indicator signal light reaches the detector through the dispersion prism basically coincides with the position of the 342nm signal light.

[0059] Step S3: Move the signal indicator light plug-in T0 out of the light path; after confirming that the light polarization state is correct, by moving the electric translation stage 6, use an oscilloscope to observe and find the difference frequency signal irradiated into the photomultiplier tube T4, and then obtain the distribution diagram of the intensity of the difference frequency signal light with the delay time (that is, the intensity distribution curve of the difference frequency signal light).

[0060] Specifically, in the process of moving the electric translation stage 6 , a curve showing the change of signal intensity with the position of the stage can be seen on the oscilloscope, that is, a distribution diagram of the intensity of the difference frequency signal light with the delay time.

[0061] The typical distribution diagram of the intensity of the 257nm ultraviolet driving laser pulse obtained by the ultraviolet picosecond laser pulse time domain diagnosis system for the free electron laser device of the utility model and the delay time is as follows: Figure 2 As shown. Figure 2 In the example, the stage moves 0.15 mm, and the corresponding delay time is 1 ps. After obtaining the intensity distribution curve of the difference frequency signal light, the half-height full width of the intensity distribution curve of the difference frequency signal light can be obtained. , and then obtain the pulse width of the light to be measured .

[0062] Pulse width of the light to be measured The calculation formula is:

[0063] ,

[0064] in, is the full width at half maximum of the intensity distribution curve of the difference frequency signal light, is the pulse width of the probe light, which is a known quantity, is the pulse width of the light to be measured.

[0065] The ultraviolet picosecond laser pulse time domain diagnostic system of the free electron laser device of the utility model adopts a BBO crystal with a thickness of 0.1mm and a crystal cutting angle of 42.2°, so that the 1030nm probe light and the 257nm ultraviolet light to be measured pass through the BBO crystal in a colinear manner to generate a difference frequency signal of about 342nm. Among them, the signal indicator light plug-in obtains the signal indicator light by coupling the external 360nm light source with the optical fiber and collimating the output, so as to achieve colinearity with the light to be measured. This colinear setting can directly and efficiently determine the position of the 342nm signal light, and adjust the position of the photomultiplier tube according to the position of the indicator signal light. In addition, the pulse width of the probe light of the ultraviolet picosecond laser pulse time domain diagnostic system of the free electron laser device of the utility model is about 100fs, and under the condition of low energy of the probe light, a high-sensitivity photomultiplier tube is used as a detector to improve the sensitivity of the measurement system.

[0066] The utility model has high time resolution (<100fs) and high scanning efficiency (on the order of ten seconds), and can realize real-time online monitoring of ultraviolet picosecond laser pulses.

[0067] The utility model applies a light source close to the signal light wavelength of 342nm externally, outputs light with a wavelength of 360nm, and inputs it into the diagnostic optical path through a signal indicator light plug-in to locate the position of the photodetector, then moves the signal indicator light plug-in out of the diagnostic optical path, and then performs time domain diagnosis of ultraviolet pulses, thereby overcoming the problem that the probe light energy is too small to determine the position of the signal light. Therefore, for test conditions that neither have high pulse energy to directly observe the signal light position nor can find the signal light through convenient difference and frequency doubling design (such as the probe light wavelength is 1030nm and the wavelength of the light to be measured is 257nm), it is still possible to achieve online real-time pulse width diagnosis of ultraviolet laser pulses and improve the time resolution and accuracy of the measurement results.

[0068] The above description is only a preferred embodiment of the utility model, and is not intended to limit the scope of the utility model. The above embodiments of the utility model can also be modified in various ways. All simple, equivalent changes and modifications made according to the claims and the contents of the specification of the utility model application fall within the scope of protection of the claims of the utility model patent. The conventional technical contents are not described in detail in the utility model.

Claims

1. A time domain diagnostic system for ultraviolet picosecond laser pulses of a free electron laser device, characterized in that: It includes an oscillator, an amplifier, a quadruple frequency module, an ultraviolet laser pulse time-domain shaping module and a diagnostic system connected in sequence; the oscillator is configured to output probe light and input light of the amplifier, the quadruple frequency module is configured to convert the output light of the amplifier into an ultraviolet laser pulse by frequency conversion, and the ultraviolet laser pulse time-domain shaping module stretches the ultraviolet driving laser pulse to a picosecond pulse width required for driving the laser, and inputs it into the diagnostic system as the light to be measured; The diagnostic system comprises a half-wave plate, a polarization beam splitter, a first infrared plane high-reflection mirror, a second infrared plane high-reflection mirror, a third infrared plane high-reflection mirror, a fourth infrared plane high-reflection mirror, a fifth infrared plane high-reflection mirror and a sixth infrared plane high-reflection mirror, an infrared lens, a signal indicator light plug-in that can be moved in and out of the optical path, a beam combiner, a BBO crystal, a dispersion prism, a bandpass filter and a photomultiplier tube, which are arranged in sequence along the optical path of the probe light. The photomultiplier tube is connected to an oscilloscope, and an optical path of the light to be measured is provided between the beam combiner and the output end of the ultraviolet laser pulse time domain shaping module and an ultraviolet lens is provided. When the probe light and the light to be measured meet the phase matching condition in the BBO crystal, 342nm signal light will be generated. The dispersion prism and the bandpass filter are used to separate the signal light and transmit it to the photomultiplier tube. When the signal indicator light plug-in is moved into the optical path, the signal indicator light and the light to be measured are collinear downstream of the beam combiner, and the photomultiplier tube is arranged at the spot position of the signal indicator light.

2. The ultraviolet picosecond laser pulse time domain diagnostic system of the free electron laser device according to claim 1, characterized in that: The wavelength of the light to be measured is 257nm, and the wavelength of the probe light is 1030nm, so that when the probe light and the light to be measured meet the time and space overlap in the BBO crystal, a signal light with a wavelength of 342nm is generated; the signal indicator light plug-in is an optical fiber and is coupled with an external 360nm light source to collimate and output a signal indicator light with a wavelength of 360nm.

3. The ultraviolet picosecond laser pulse time domain diagnostic system of the free electron laser device according to claim 1, characterized in that: The thickness of the BBO crystal is at most 0.1 mm, and the cutting angle is =42.2°.

4. The ultraviolet picosecond laser pulse time domain diagnostic system of the free electron laser device according to claim 1, characterized in that: The polarization state of the probe light is perpendicular to the polarization state of the light to be measured, the probe light is o light, and the light to be measured is e light; the half-wave plate and the polarization beam splitter are used to determine the polarization state of the probe light, thereby ensuring that the polarization state of the probe light is adjusted to horizontal polarization.

5. The ultraviolet picosecond laser pulse time domain diagnostic system of the free electron laser device according to claim 1, characterized in that: The first infrared plane high reflective mirror and the second infrared plane high reflective mirror are directly opposite to each other, and the incident angles of the light to be measured on the first infrared plane high reflective mirror and the second infrared plane high reflective mirror are set to be less than 10°, so that the combination of the first infrared plane high reflective mirror and the second infrared plane high reflective mirror is used to adjust the optical path difference of the probe light relative to the light to be measured, and the adjustment range of the optical path difference between the first infrared plane high reflective mirror and the second infrared plane high reflective mirror is 1ns to 15ns.

6. The ultraviolet picosecond laser pulse time domain diagnostic system of the free electron laser device according to claim 1, characterized in that: The fifth infrared plane high-reflection mirror and the sixth infrared plane high-reflection mirror are installed on the same electric translation stage, so as to achieve the temporal overlap of the light to be measured and the probe light by controlling the movement of the electric translation stage; the electric translation stage is also configured to enable the oscilloscope to collect the distribution curve between the intensity of the signal light and the position of the high-precision delay line as the intensity distribution curve of the difference frequency signal light during scanning, and the half-height full width of the intensity distribution curve of the difference frequency signal light is The pulse width of the light to be measured The relationship is: ， in, is the full width at half maximum of the intensity distribution curve of the difference frequency signal light, is the pulse width of the probe light.

7. The ultraviolet picosecond laser pulse time domain diagnostic system of the free electron laser device according to claim 6, characterized in that: The scanning range of the electric translation stage is 0 mm-400 mm, and the minimum displacement increment of the scanning is 30 nm.

8. The ultraviolet picosecond laser pulse time domain diagnostic system of the free electron laser device according to claim 1, characterized in that: The signal indicator light plug-in is installed on a quickly disassembled four-dimensional optical adjustment frame, and the four-dimensional optical adjustment frame is used to realize the colinearity of the signal indicator light and the light to be measured.

9. The ultraviolet picosecond laser pulse time domain diagnostic system of a free electron laser device according to claim 1, characterized in that: The BBO crystal is mounted on a crystal optical adjustment frame.

10. The ultraviolet picosecond laser pulse time domain diagnostic system of a free electron laser device according to claim 1, characterized in that: The pulse width of the probe light is 50-200 femtoseconds, the average power is 10-150 milliwatts, the repetition frequency is 0.1-100 MHz, and the single pulse energy is 1-10 nanojoules.

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