Dynamic performance calibration system and method for fast scanning gear of streak camera

Abstract

The invention relates to a dynamic performance calibration system for a streak camera fast scanning gear, which is mainly used for solving the problems that the operation is complicated when a plurality of pulse strings are generated in an existing mode of beam combination after beam splitting, the consistency of optical path differences among all optical paths is difficult to guarantee, and a conventional electric signal triggering mode shakes, so that the calibration precision is poor. And the calibration of the time resolution capability of the streak camera is influenced. According to the invention, a plurality of optical pulse strings can be generated at the same time, and the time interval consistency among the plurality of optical pulse strings is high. Wherein a light pulse output by the laser is divided into a transmitted first light beam and a reflected second light beam through the spectroscope, the second light beam is input into the fast response photodiode and then is converted into an electric pulse, and the streak camera is triggered to work; the first light beam is input into the streak camera through the F-P etalon, and the reading camera reads and analyzes a streak image output by the streak camera. The invention further provides a dynamic performance calibration method for the fast scanning gear of the streak camera.

Description

Technical Field

[0001] The present invention relates to a streak camera calibration system and method, and in particular to a dynamic performance calibration system and method for a streak camera fast scanning gear. Background Art

[0002] A streak camera is an instrument for measuring transient optical processes with both high temporal resolution and high spatial resolution. It can convert time information into spatial information to achieve ultrafast diagnosis. Its time resolution capability covers the microsecond to sub-picosecond (femtosecond) range, and it has important applications in basic scientific research and major national scientific facilities.

[0003] As an ultrafast diagnostic instrument, the streak camera works by using a photocathode to convert light signals into electronic signals. The electronic signals are accelerated and deflected under the action of the electric field in the streak image converter to form a streak image. According to its principle, multiple time windows (scanning gears) can be obtained by applying ramp voltages with different scanning speeds to the scanning electrode of the streak image converter. For different scanning gears, it is necessary to calibrate the various performances of each gear before use. When applying a streak camera to an ultrafast diagnostic system, its dynamic performance calibration is a necessary task before application, including quantitative measurement of time resolution, camera full-screen time range and dynamic range, so as to analyze the experimental data.

[0004] The fast scan gear usually refers to the working mode in which the camera time window is below 5ns. At this time, the temporal resolution capability of the streak camera is extremely high, and the stability of the trigger signal is extremely high. In the prior art, the light pulse is usually split, a certain optical path difference is created in the two light paths, and then the beams are combined to generate two light pulse trains with a certain time interval. However, this method can generally only generate two light pulse trains. For three or more light pulse trains, multiple splitting and multiple combining are required. At the same time, the consistency of the optical path difference between each light path is difficult to ensure. In addition, the electrical signal generated by the calibration light source itself usually used in the prior art has time jitter, so the use of conventional electrical signal triggering will affect the calibration of the temporal resolution capability of the streak camera. Summary of the invention

[0005] The purpose of the present invention is to solve the technical problems that when calibrating the time resolution capability of the fast scanning gear of the existing streak camera, the operation of generating multiple pulse trains by the method of splitting and then combining is complicated, the consistency of the optical path difference between each optical path is difficult to ensure, and the conventional electrical signal triggering method has jitter, which affects the calibration of the time resolution capability. A dynamic performance calibration system and method for the fast scanning gear of the streak camera are proposed.

[0006] To solve the above technical problems, the technical solutions provided by the present invention are as follows:

[0007] A dynamic performance calibration system for a streak camera fast scanning gear includes a streak camera, and is special in that it also includes a laser, a spectroscope, a fast response photodiode, and an FP standard tool readout camera;

[0008] The laser is used to output light pulses;

[0009] The beam splitter is located on the optical path of the laser output light pulse, and the light pulse is divided into a transmitted first light beam and a reflected second light beam by the beam splitter;

[0010] The FP etalon comprises two parallel reflectors, the distance between the two reflectors is L; the two reflectors are located on the transmission light path of the beam splitter, and are used to receive the first light beam and output a plurality of light pulse trains with equal time intervals and decreasing intensities; the streak camera is located on the output light path of the FP etalon;

[0011] The fast response photodiode is located on the reflection light path of the spectroscope, and is used to receive the second light beam and output an electrical pulse; the output end of the fast response photodiode is connected to the trigger end of the streak camera, and is used to trigger the streak camera to work;

[0012] The streak camera receives the light pulse train, converts it into equidistant fringes, and outputs a streak image;

[0013] The readout camera includes an image plane composed of M×M pixels. The input end of the readout camera is connected to the output end of the streak camera, and is used to read the streak image through the image plane and convert it into a digital signal, which is transmitted to an external computer for analysis and calculation to obtain the calibration result of the dynamic performance of the fast scanning gear of the streak camera.

[0014] Furthermore, it also includes a first reflector; the first reflector is located on the reflected light path of the spectroscope; the fast response photodiode is located on the reflected light path of the first reflector, and is used to receive the second light beam and output an electrical pulse.

[0015] Furthermore, the streak camera is of picosecond to sub-picosecond magnitude;

[0016] The laser is a femtosecond laser, which outputs light pulses with a time width of femtoseconds.

[0017] Furthermore, it also includes frosted glass, which is located between the FP etalon and the streak camera and is used to homogenize the light pulse train and broaden the light pulse train in the spatial direction.

[0018] Furthermore, the transmission-reflection ratio of the two reflectors of the FP etalon is 3:7.

[0019] The present invention also provides a dynamic performance calibration method for a streak camera fast scanning gear, based on the above-mentioned dynamic performance calibration system for a streak camera fast scanning gear, which is special in that it includes time resolution calibration, full screen time calibration and dynamic range calibration, and specifically includes the following steps:

[0020] Step 1: Collect the output image of the streak camera

[0021] The light pulse emitted by the laser is divided into a first light beam and a second light beam by a spectroscope; the first light beam generates a plurality of light pulse trains with equal time intervals and proportionally reduced intensities through the FP standard device and is incident on the streak camera; at the same time, the second light beam generates an electric pulse through a fast response photodiode to trigger the streak camera to work; the streak camera converts the received light pulse train into equidistant stripes and outputs a stripe image; the readout camera collects the stripe image output by the streak camera;

[0022] Step 2: Calibrate the dynamic performance of the streak camera at the fast scanning position

[0023] The dynamic performance calibration of the streak camera in fast scanning gear includes time resolution calibration, full screen time calibration and dynamic range calibration;

[0024] A) Time resolution calibration:

[0025] A1) The FP etalon generates multiple optical pulse trains with equal time intervals, the time interval is Δt. The formula for calculating the time interval Δt is:

[0026] Δt=2L / c;

[0027] Where c is the speed of light and L is the distance between the two reflectors;

[0028] A2) Analyze the fringe image read by the readout camera, and obtain that the signal peak interval corresponding to the time interval Δt is N pixels, and the half-maximum full width of the narrowest light pulse train is n pixels. The calculation formula of the temporal resolution τ of the streak camera is:

[0029] τ=(n / N)·Δt;

[0030] Complete the calibration of time resolution;

[0031] B) Full screen time calibration:

[0032] The full screen time refers to the time range that the streak camera can record; the streak image read by the readout camera is analyzed, and the signal peak interval corresponding to the time interval Δt is obtained as N pixels; the full screen time T of the streak camera is obtained;

[0033] T = (M / N) · Δt;

[0034] Where M is the pixel value in the time direction of the readout camera image plane, and the time direction refers to the direction parallel to the deflection plate of the streak camera;

[0035] C) Dynamic Range:

[0036] After the image output by the streak camera is de-noised, the ratio of its maximum brightness to its minimum brightness is the dynamic range of the streak camera. The dynamic range is calculated as follows:

[0037] DR=(Imax-Inoise) / (Imin-Inoise);

[0038] Among them, DR represents dynamic range, Imax represents maximum brightness, Inoise represents noise intensity, and Imin represents minimum brightness.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. In a dynamic performance calibration system for a fast scanning position of a streak camera of the present invention, the light pulse output by the laser is divided into a transmitted first light beam and a reflected second light beam by a spectroscope, the second light beam is input to a fast response photodiode, the fast response photodiode converts it into an electrical signal, outputs an electrical pulse, and triggers the streak camera to work; the first light beam is input to the streak camera via an FP etalon, and the readout camera reads and analyzes the streak image output by the streak camera. The FP etalon can realize the simultaneous generation of multiple light pulse trains, and the time intervals between the multiple light pulse trains are highly consistent.

[0041] 2. The present invention discloses a dynamic performance calibration system for a streak camera in a fast scanning position, which uses a femtosecond laser as a calibration light source. Compared with the prior art, the femtosecond laser can eliminate the jitter of the laser's own electrical signal and meet the high requirements of the streak camera for the stability of the trigger signal in the fast scanning position.

[0042] 3. In the dynamic performance calibration system for the fast scanning position of a streak camera of the present invention, the FP etalon is used. Compared with the use of a length measuring interferometer, multiple step adjustments are required until the time is indistinguishable. The FP etalon of the present invention is an interferometer with a known spacing L, which does not require repeated adjustments. During the calibration process, the time resolution can be calculated based on the spacing L, which simplifies the calibration process.

[0043] 4. The present invention provides a dynamic performance calibration method for a streak camera fast scan position, which can simultaneously calibrate the lower limit time resolution capability, dynamic range and camera full screen time of the streak camera, and provide accurate performance indicators.

[0044] 5. In the dynamic performance calibration method for the fast scanning gear of a streak camera of the present invention, the brightness of the multiple light pulse trains generated by the FP standard tool gradually decreases, and the intensity thereof decreases proportionally, which is convenient for testing the dynamic range. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 A connection diagram of an embodiment of a dynamic performance calibration system for a streak camera fast scanning position according to the present invention;

[0046] Figure 2 A streak image output by a streak camera in an embodiment of a method for calibrating the dynamic performance of a streak camera at a fast scanning position of the present invention;

[0047] Figure 3 It is an integral image of a streak image output by a streak camera in an embodiment of a method for calibrating the dynamic performance of a streak camera at a fast scanning position of the present invention;

[0048] Figure 4 The diagram is a schematic diagram of an optical pulse train output by an FP etalon in an embodiment of a dynamic performance calibration system for a streak camera fast scanning position of the present invention.

[0049] Description of reference numerals:

[0050] 1. Laser; 2. Spectrometer; 3. First reflector; 4. FP etalon; 5. Ground glass; 6. Streak camera; 7. Readout camera; 8. Fast response photodiode; 9. Computer. DETAILED DESCRIPTION

[0051] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0052] The present invention provides a dynamic performance calibration system and method for a streak camera fast scanning position, such as Figure 1 As shown, it includes a laser 1, a spectrometer 2, a first reflector 3, a fast response photodiode 8, an FP etalon 4, a ground glass 5, a streak camera 6 and a readout camera 7.

[0053] The laser 1 is used as a calibration light source in the calibration system to generate light pulses with a time width of femtoseconds. In order to ensure that the performance of the calibration light source does not affect the time resolution of the streak camera 6 itself, a delta pulse light source with a limited light flux and an infinitely narrow width is generally used as an ideal test light source. The calibration light source usually refers to a light pulse whose duration is much lower than the time resolution capability of the camera to be tested. In this embodiment, the streak camera 6 is in the picosecond to sub-picosecond range, and a femtosecond laser with a pulse width in the femtosecond range is used as an ideal light source for the performance calibration of the streak camera 6.

[0054] The beam splitter 2 receives the light pulse and divides it into a first light beam and a second light beam. The first light beam is the transmitted light, which enters the FP etalon 4 after being output by the beam splitter 2; the second light beam is the reflected light, which enters the first reflector 3 after being reflected by the beam splitter 2;

[0055] The second light beam is reflected by the first reflector and then enters the fast response photodiode 8. The fast response photodiode 8 is a photoelectric conversion device with fast response capability, which is used to convert light signals into electrical signals. It has the characteristics of fast response speed, high sensitivity and low noise. The fast response photodiode 8 outputs an electrical pulse, which serves as a trigger signal to trigger the streak camera 6 to work.

[0056] The FP etalon 4 includes two parallel reflectors, the distance between the two reflectors is L, and the transmission-reflection ratio is 3:7. Figure 4 As shown, the first light beam reflects back and forth in the FP etalon 4, outputting multiple light pulse trains with equal time intervals and decreasing intensities. By adjusting the distance L between the two reflectors in the FP etalon 4, the time interval of the light pulse train can be changed, thereby achieving calibration of different time positions.

[0057] The optical pulse train is input to the streak camera 6 for imaging through the frosted glass 5. The frosted glass 5 plays the role of homogenizing the optical pulse train, which can reduce the damage of the high-energy laser spot in the optical pulse train to the streak camera 6, and at the same time, widens the light spot in the spatial direction, making the streak image output by the streak camera 6 easier to analyze.

[0058] The light pulse train is converted into equidistant fringes by the streak camera 6, which are imaged on the fluorescent screen of the streak camera 6 and then read by the readout camera 7; the readout camera 7 transmits and stores the fringes image to the external computer 9 for analysis and calculation to obtain the various dynamic performances of the streak camera 6.

[0059] The present invention also provides a dynamic performance calibration method for a fast scanning position of a streak camera, including A time resolution calibration, B full screen time calibration and C dynamic range calibration, specifically including the following steps:

[0060] Step 1: Collect the output image of the streak camera

[0061] The laser 1 emits a light pulse which is divided into a first light beam and a second light beam by a beam splitter 2; the first light beam generates a plurality of light pulse trains with equal time intervals and proportionally reduced intensities through an FP etalon 4 and is incident on a streak camera 6; at the same time, the second light beam generates an electric pulse through a fast response photodiode 8 to trigger the streak camera 6 to work; the streak camera 6 converts the received light pulse train into equidistant stripes and outputs a stripe image; the readout camera 7 collects the stripe image output by the streak camera 6;

[0062] Step 2: Calibrate the dynamic performance of the streak camera at the fast scanning position

[0063] The dynamic performance calibration of the streak camera in fast scanning gear includes time resolution calibration, full screen time calibration and dynamic range calibration;

[0064] A) Time resolution calibration:

[0065] The temporal resolution capability of the streak camera 6 refers to the minimum time interval between two optical pulse trains that the streak camera 6 can resolve. The imaging of the calibration light source on the streak camera 6 will be broadened. If two optical pulse trains with time sequence enter the streak camera 6 and satisfy the Rayleigh criterion in the time axis direction, the time interval between the two optical pulse trains is considered to be resolvable. In actual calibration and performance testing, for femtosecond laser pulses that satisfy the Gaussian distribution, the full width at half maximum (FWHM) of the optical pulse train is usually used to describe its width. The full width at half maximum of the Gaussian light pulse must be at least 1 / 4 of the full width at half maximum of the temporal resolution of the streak camera. Therefore, the full width at half maximum after the calibration light source is broadened is equivalent to the minimum interval of the optical pulse train that the streak camera 6 can resolve, that is, the temporal resolution capability.

[0066] A1) Using the FP etalon 4 to generate a plurality of optical pulse trains with equal time intervals, the time interval Δt can be changed by adjusting the spacing L of the FP etalon 4. The formula for calculating the time interval Δt is:

[0067] Δt=2L / c;

[0068] Where c is the speed of light;

[0069] A2) After obtaining the time interval Δt of each pulse, the fringe image read by the readout camera 7 is analyzed and obtained, and the signal peak interval of the time interval Δt is N pixels, and the half-maximum full width of the narrowest light pulse is n pixels; then the calculation formula of the time resolution capability τ of the streak camera 6 is:

[0070] τ=(n / N)·Δt;

[0071] Complete the calibration of time resolution;

[0072] B) Full screen time calibration:

[0073] The full screen time refers to the time range that the streak camera 6 can record; after obtaining the time interval Δt of each pulse, the width of the streak image read by the readout camera 7 is analyzed to obtain the full screen time T of the streak camera 6 at the corresponding gear position;

[0074] The readout camera 7 is an image plane composed of M×M pixels, where the signal peak interval of the time interval Δt is N. The formula for calculating the full screen time T of the streak camera 6 is:

[0075] T = (M / N) · Δt;

[0076] Wherein, M is the pixel value of the image plane of the read-out camera 7 in the time direction, and the time direction refers to the direction parallel to the deflection plate of the streak camera;

[0077] C) Dynamic Range:

[0078] The dynamic range refers to the dynamic range of the streak camera 6 that can image objects of different brightness. After the noise is removed from the streak image output by the streak camera 6, the ratio of its maximum brightness to its minimum brightness is the dynamic range of the streak camera 6. As the brightness of the multiple light pulse trains generated by the FP etalon 4 gradually decreases, their intensity also gradually decreases. The transmission-reflection ratio of the two reflectors of the FP etalon 4 is 3:7. After two reflections, the intensity of each light pulse is 49% of the intensity of the previous light pulse. The dynamic range is calculated as follows:

[0079] DR=(Imax-Inoise) / (Imin-Inoise);

[0080] Among them, DR represents dynamic range, Imax represents maximum brightness, Inoise represents noise intensity, and Imin represents minimum brightness.

[0081] After the streak camera 6 is calibrated by the method of the present invention, the streak image output by the streak camera 6 is as follows: Figure 2 shown. Figure 2 The horizontal coordinate is the slit direction of the streak camera 6, and the vertical coordinate is the time direction of the streak camera 6. In the image analysis software, after selecting the image, the integral image can be obtained by integrating in the time direction. Figure 3 As shown, it is an integral diagram of the streak image output by the streak camera 6, wherein the horizontal axis is time and the vertical axis is image intensity. Figure 3 The multiple peaks in represent multiple optical pulse trains, and the interval between the peaks is the time delay Δt. Figure 3 From the integral curve, the dynamic performance parameters of the streak camera 6 at this scanning position, such as the time resolution, full-screen time range, and dynamic range, can be obtained.

Claims

1. A dynamic performance calibration system for a streak camera fast scanning position, comprising a streak camera (6), characterized in that: It also includes a laser (1), a spectroscope (2), a fast response photodiode (8), an FP etalon (4) and a readout camera (7); The laser (1) is used to output light pulses; The beam splitter (2) is located on the optical path of the light pulse output by the laser (1), and the light pulse is split into a transmitted first light beam and a reflected second light beam by the beam splitter (2); The FP etalon (4) comprises two parallel reflectors, the distance between the two reflectors being L; the two reflectors are located on the transmission light path of the beam splitter (2), and are used to receive the first light beam and output a plurality of light pulse trains with equal time intervals and decreasing intensities; the streak camera (6) is located on the output light path of the FP etalon (4); The fast response photodiode (8) is located on the reflection light path of the spectroscope (2) and is used to receive the second light beam and output an electrical pulse; the output end of the fast response photodiode (8) is connected to the trigger end of the streak camera (6) and is used to trigger the streak camera (6) to work; The streak camera (6) receives the light pulse train, converts it into equidistant fringes, and outputs a streak image; The readout camera (7) comprises an image plane composed of M×M pixels. The input end of the readout camera (7) is connected to the output end of the streak camera (6) and is used to read the streak image through the image plane and convert it into a digital signal, which is transmitted to an external computer (9) for analysis and calculation to obtain a calibration result of the dynamic performance of the fast scanning gear of the streak camera.

2. A dynamic performance calibration system for a streak camera fast scanning position according to claim 1, characterized in that: It also includes a first reflector (3); the first reflector (3) is located on the reflected light path of the beam splitter (2); the fast response photodiode (8) is located on the reflected light path of the first reflector (3) and is used to receive the second light beam and output an electrical pulse.

3. A dynamic performance calibration system for a streak camera fast scanning position according to claim 1 or 2, characterized in that: The streak camera (6) is of picosecond to sub-picosecond magnitude; The laser (1) is a femtosecond laser that outputs light pulses with a time width of femtoseconds.

4. The dynamic performance calibration system for the fast scanning position of a streak camera according to claim 3, characterized in that: The invention also comprises a frosted glass (5), which is located between the FP etalon (4) and the streak camera (6) and is used for homogenizing the optical pulse train and widening the optical pulse train in the spatial direction.

5. The dynamic performance calibration system for the fast scanning position of a streak camera according to claim 4, characterized in that: The transmission-reflection ratio of the two reflectors of the FP etalon (4) is 3:

7.

6. A method for dynamic performance calibration of a streak camera fast scan position, based on a dynamic performance calibration system for a streak camera fast scan position according to any one of claims 1 to 4, characterized in that: Including time resolution calibration, full screen time calibration and dynamic range calibration, specifically including the following steps: Step 1: Collect the output image of the streak camera A laser (1) emits a light pulse which is divided into a first light beam and a second light beam through a beam splitter (2); the first light beam generates a plurality of light pulse trains with equal time intervals and proportionally reduced intensities through an FP standard tool (4) and is incident on a streak camera (6); at the same time, the second light beam generates an electric pulse through a fast response photodiode (8) to trigger the streak camera (6) to work; the streak camera (6) converts the received light pulse train into equidistant stripes and outputs a stripe image; a readout camera (7) collects the stripe image output by the streak camera (6); Step 2: Calibrate the dynamic performance of the streak camera at the fast scanning position The dynamic performance calibration of the streak camera in fast scanning gear includes time resolution calibration, full screen time calibration and dynamic range calibration; A) Time resolution calibration: A1) The FP etalon (4) generates a plurality of optical pulse trains with equal time intervals, the time interval being Δt. The formula for calculating the time interval Δt is: Δt=2L / c; Where c is the speed of light and L is the distance between the two reflectors; A2) Analyze the fringe image read by the readout camera (7), and obtain that the signal peak interval corresponding to the time interval Δt is N pixels, and the half-maximum full width of the narrowest light pulse train is n pixels. Then the calculation formula of the time resolution capability τ of the streak camera (6) is: τ=(n / N)·Δt; Complete the calibration of time resolution; B) Full screen time calibration: The full screen time refers to the time range that the streak camera (6) can record; the streak image read by the readout camera (7) is analyzed, and the signal peak interval corresponding to the time interval Δt is obtained as N pixels; the full screen time T of the streak camera (6) is obtained; T = (M / N) · Δt; Wherein, M is the pixel value in the time direction of the image plane of the readout camera (7), and the time direction refers to the direction parallel to the deflection plate of the streak camera; C) Dynamic Range: After the image output by the streak camera (6) is de-noised, the ratio of the maximum brightness to the minimum brightness is the dynamic range of the streak camera (6). The calculation formula of the dynamic range is: DR=(Imax-Inoise) / (Imin-Inoise); Among them, DR represents dynamic range, Imax represents maximum brightness, Inoise represents noise intensity, and Imin represents minimum brightness.

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