A dynamic performance calibration system and method for a streak camera fast scan stage

Abstract

The present application relates to a kind of dynamic performance calibration systems for streak camera fast scanning gear, mainly used to solve the technical problems that the operation is complex when multiple pulse trains are generated by the existing light splitting and beam combining mode, and the consistency of optical path difference between each light path is difficult to guarantee, and the conventional electrical signal trigger mode exists sway, influence the time resolution capability calibration of streak camera.The present application can simultaneously generate multiple optical pulse trains, and the time interval consistency between multiple optical pulse trains is high.The optical pulse output by the laser is divided into the first light beam transmitted by the beam splitter and the second light beam reflected, the second light beam is input to the fast-response photodiode, and then converted into an electrical pulse to trigger the streak camera to work.The first light beam is input to the streak camera through the F-P standard device, and the streak camera reads the streak image output by the streak camera and analyzes it.The present application also provides a kind of dynamic performance calibration method for streak camera fast scanning gear.

Description

Technical Field

[0001] This invention relates to a streak camera calibration system and method, specifically to a dynamic performance calibration system and method for the fast scan mode of a streak camera. Background Technology

[0002] A streak camera is a transient optical process measurement instrument that has both high temporal and spatial resolution. It can convert time information into spatial information to achieve ultrafast diagnosis. Its temporal resolution capability covers the range from microseconds to sub-picoseconds (femtoseconds), 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 converting light signals into electronic signals using a photocathode. These electronic signals are accelerated and deflected by the electric field within the streak image inductor tube, forming a streak image. Based on this principle, multiple time windows (scanning levels) can be obtained by applying ramp voltages of different scanning speeds to the scanning plates of the streak image inductor tube. For each scanning level, its performance characteristics need to be calibrated before use. When applying a streak camera to an ultrafast diagnostic system, dynamic performance calibration is essential before application. This includes quantitative measurements of time resolution, the camera's full-screen time range, and dynamic range to facilitate experimental data analysis.

[0004] Fast scan mode typically refers to a camera operating mode with a time window of less than 5ns. In this mode, the streak camera's time resolution is extremely high, requiring extremely stable trigger signals. Current technology usually involves splitting the light pulse, creating a certain optical path difference between the two beams, and then combining them 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 combining are required, and ensuring the consistency of the optical path difference between the various optical paths is difficult. Furthermore, the electrical signals generated by the calibration light source itself, which are commonly used in current technology, exhibit temporal fluctuations. Therefore, using conventional electrical signal triggering methods will affect the calibration of the streak camera's time resolution. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problems of existing streak camera fast scan mode time resolution calibration, which uses beam splitting and beam combining to generate multiple pulse trains, which is complicated and difficult to ensure the consistency of optical path difference between each optical path, and the use of conventional electrical signal triggering method has jitter, affecting the time resolution calibration. The invention proposes a dynamic performance calibration system and method for streak camera fast scan mode.

[0006] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0007] A dynamic performance calibration system for the fast scan mode of a stripe camera includes a stripe camera, and is characterized in that it also includes a laser, a beam splitter, a fast-response photodiode, and an FP etalon readout camera.

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

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

[0010] The FP etalon includes two parallel reflectors with a distance L between them; the two reflectors are located on the transmission optical path of the beam splitter to receive the first beam and output multiple light pulse trains with equal time intervals and progressively decreasing intensity; the streak camera is located on the output optical path of the FP etalon.

[0011] The fast-response photodiode is located in the reflected light path of the beam splitter and is used to receive the second beam and output electrical pulses; the output terminal of the fast-response photodiode is connected to the trigger terminal of the stripe camera to trigger the stripe camera to work.

[0012] The stripe camera receives light pulse trains and converts them into equidistant stripes, outputting a stripe 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 stripe camera. It is used to read stripe images through the image plane and convert them into digital signals, which are then transmitted to an external computer for analysis and calculation to obtain the calibration results of the dynamic performance of the stripe camera's fast scan mode.

[0014] Furthermore, it also includes a first reflecting mirror; the first reflecting mirror is located in the reflected light path of the beam splitter; the fast-response photodiode is located in the reflected light path of the first reflecting mirror, and is used to receive the second beam and output electrical pulses.

[0015] Furthermore, the stripe camera is in the picosecond to sub-picosecond range;

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

[0017] Furthermore, it also includes a frosted glass, located between the FP etalon and the streak camera, for homogenizing the light pulse train and widening the light pulse train in the spatial direction.

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

[0019] This invention also provides a dynamic performance calibration method for the fast scan mode of a streak camera. Based on the above-mentioned dynamic performance calibration system for the fast scan mode of a streak camera, its special feature is that it includes time resolution calibration, full-screen time calibration, and dynamic range calibration, specifically including the following steps:

[0020] Step 1: Acquire the output image from the stripe camera.

[0021] The laser emits light pulses which are split into a first beam and a second beam by a beam splitter. The first beam is transmitted through an FP etalon to generate multiple light pulse trains with equal time intervals and proportionally decreasing in intensity, which are then incident on the stripe camera. Simultaneously, the second beam is transmitted through a fast-response photodiode to generate electrical pulses, which trigger the stripe camera to operate. The stripe camera converts the received light pulse trains into equidistant stripes and outputs a stripe image. The readout camera acquires the stripe image output by the stripe camera.

[0022] Step 2: Calibrate the dynamic performance of the stripe camera at the fast scan setting.

[0023] The dynamic performance calibration of the fast scan mode of the stripe camera includes time resolution calibration, full-screen time calibration, and dynamic range calibration;

[0024] A) Time resolution calibration:

[0025] A1) The FP standard generates multiple light pulse trains with equal time intervals, the time interval being 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 mirrors;

[0028] A2) Analyzing the stripe image read by the readout camera, we find that the signal peak interval corresponding to the time interval Δt is N pixels, and the full width at half maximum (FWHM) of the narrowest light pulse train is n pixels. Therefore, the formula for calculating the temporal resolution τ of the stripe camera is:

[0029] τ=(n / N)·Δt;

[0030] The calibration of time resolution capability was completed;

[0031] B) Full-screen time calibration:

[0032] Full-screen time refers to the time range that the stripe camera can record; analyze the stripe image read by the readout camera, obtain the signal peak interval corresponding to the time interval Δt as N pixels; and obtain the full-screen time T of the stripe camera;

[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 fringe camera.

[0035] C) Dynamic range:

[0036] After noise removal, the ratio of the maximum to the minimum brightness value of the image output by the streak camera is the dynamic range of the streak camera. The formula for calculating the dynamic range is:

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

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

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] 1. In a dynamic performance calibration system for the fast scan mode of a streak camera, the laser output light pulse is split into a transmitted first beam and a reflected second beam by a beam splitter. The second beam is input to a fast-response photodiode, which converts it into an electrical signal and outputs an electrical pulse to trigger the streak camera. The first 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 simultaneously generate multiple light pulse trains with high consistency in the time intervals between the multiple light pulse trains.

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

[0042] 3. In the dynamic performance calibration system for the fast scan mode of a streak camera of the present invention, the FP etalon is used. Compared with the use of a length measuring interferometer, which requires multiple step adjustments until the time is indistinguishable, the FP etalon in the present invention is an interferometer with a known spacing L, which eliminates the need for repeated adjustments. The time resolution can be calculated from the spacing L during the calibration process, simplifying the calibration process.

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

[0044] 5. In the dynamic performance calibration method for fast scan mode of a stripe camera, the brightness of multiple light pulse trains generated by the FP etalon gradually decreases, and their intensity decreases proportionally, which facilitates the testing of dynamic range. Attached Figure Description

[0045] Figure 1 This is a connection diagram of an embodiment of a dynamic performance calibration system for fast scan mode of a stripe camera according to the present invention;

[0046] Figure 2 This is a stripe image output by a stripe camera in an embodiment of a dynamic performance calibration method for fast scan mode of a stripe camera according to the present invention.

[0047] Figure 3 This is an integral image of the stripe image output by the stripe camera in an embodiment of the dynamic performance calibration method for the fast scan mode of a stripe camera according to the present invention.

[0048] Figure 4 This is a schematic diagram of the light pulse train output by the FP etalon in an embodiment of a dynamic performance calibration system for fast scan mode of a stripe camera according to the present invention.

[0049] Explanation of reference numerals in the attached figures:

[0050] 1. Laser; 2. Beam splitter; 3. First reflecting mirror; 4. FP etalon; 5. Frosted glass; 6. Streak camera; 7. Readout camera; 8. Fast response photodiode; 9. Computer. Detailed Implementation

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

[0052] This invention discloses a dynamic performance calibration system and method for the fast scan mode of a streak camera, such as... Figure 1 As shown, it includes a laser 1, a beam splitter 2, a first reflector 3, a fast-response photodiode 8, an FP etalon 4, a frosted glass 5, a stripe camera 6, and a readout camera 7.

[0053] Laser 1 serves as the calibration light source in the calibration system, used to generate light pulses with a time width of femtoseconds. 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 finite luminous flux and infinitely narrow pulse width is generally used as the ideal test light source. The calibration light source usually refers to a light pulse duration that is much shorter than the time resolution capability of the camera under test. 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 the ideal light source for calibrating the performance of the streak camera 6.

[0054] Beam splitter 2 receives the light pulse and splits it into a first beam and a second beam. The first beam is transmitted light and enters the FP etalon 4 after being output by beam splitter 2. The second beam is reflected light and enters the first reflecting mirror 3 after being reflected by beam splitter 2.

[0055] The second beam of light is reflected by the first reflecting mirror and then enters the fast-response photodiode 8. The fast-response photodiode 8 is a photoelectric conversion device with fast response capability, used to convert optical signals into electrical signals. It features fast response speed, high sensitivity, and low noise. The fast-response photodiode 8 outputs electrical pulses, which serve as trigger signals to activate the stripe camera 6.

[0056] The FP etalon 4 consists of two parallel reflectors spaced L apart, with a transmission-to-reflection ratio of 3:7. For example... Figure 4 As shown, the first beam is reflected back and forth within the FP etalon 4, outputting multiple light pulse trains with equal time intervals and progressively decreasing intensity. Adjusting the distance L between the two reflectors in the FP etalon 4 changes the time interval of the light pulse trains, thereby enabling calibration at different time settings.

[0057] The light pulse train is input to the streak camera 6 through the frosted glass 5. The frosted glass 5 plays the role of homogenizing the light pulse train, which can reduce the damage of the high-energy laser spots in the light pulse train to the streak camera 6. At the same time, it 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 stripes by the stripe camera 6, which are then imaged on the fluorescent screen of the stripe camera 6 and read by the readout camera 7. The readout camera 7 transmits and stores the stripe image to an external computer 9 for analysis, and calculates and obtains various dynamic performance parameters of the stripe camera 6.

[0059] This invention also provides a dynamic performance calibration method for the fast scan mode 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: Acquire the output image from the stripe camera.

[0061] Laser 1 emits light pulses which are split into a first beam and a second beam by beam splitter 2. The first beam passes through FP etalon 4 to generate multiple light pulse trains with equal time intervals and proportionally decreasing intensity, which are then incident on stripe camera 6. At the same time, the second beam generates electrical pulses through fast-response photodiode 8, which triggers stripe camera 6 to work. Stripe camera 6 converts the received light pulse trains into equidistant stripes and outputs a stripe image. Readout camera 7 acquires the stripe image output by stripe camera 6.

[0062] Step 2: Calibrate the dynamic performance of the stripe camera at the fast scan setting.

[0063] The dynamic performance calibration of the fast scan mode of the stripe camera includes time resolution calibration, full-screen time calibration, and dynamic range calibration;

[0064] A) Time resolution calibration:

[0065] The temporal resolution of the streak camera 6 refers to the minimum time interval between two optical pulse trains that the streak camera 6 can resolve. The image of the calibration light source on the streak camera 6 will broaden. If two sequentially occurring optical pulse trains enter the streak camera 6 and satisfy the Rayleigh criterion along the time axis, then the time interval between these two optical pulse trains is considered resolvable. In actual calibration and performance testing, for femtosecond laser pulses that satisfy a Gaussian distribution, their width is usually described using the full width at half maximum (FWHM) of the pulse train. The FWHM of a Gaussian optical pulse must be at least 1 / 4 of the temporal resolution FWHM of the streak camera. Therefore, the broadened FWHM of the calibration light source is equivalent to the minimum interval between optical pulse trains that the streak camera 6 can resolve, i.e., its temporal resolution.

[0066] A1) Multiple light pulse trains with equal time intervals are generated using the FP etalon 4. The time interval is Δt, which 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, analyze the stripe image read by the readout camera 7. The signal peak interval of time interval Δt is N pixels, and the full width at half maximum (FWHM) of the narrowest light pulse is n pixels. Therefore, the formula for calculating the time resolution τ of the stripe camera 6 is:

[0070] τ=(n / N)·Δt;

[0071] The calibration of time resolution capability was completed;

[0072] B) Full-screen time calibration:

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

[0074] The readout camera 7 has 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 stripe camera 6 is:

[0075] T = (M / N)·Δt;

[0076] Where 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 stripe camera.

[0077] C) Dynamic range:

[0078] Dynamic range refers to the range within which the stripe camera 6 can image an object at different brightness levels. After noise removal, the ratio of the maximum to minimum brightness value of the stripe image output by the stripe camera 6 is the dynamic range of the stripe camera 6. Since the brightness of the multiple light pulse trains generated by the FP etalon 4 gradually decreases, their intensity also gradually decreases. Given that the transmission-to-reflection ratio of the two mirrors 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 formula for calculating the dynamic range is:

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

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

[0081] After the stripe camera 6 is calibrated using the method of this invention, the stripe image output by the stripe camera 6 is as follows: Figure 2 As shown. Figure 2 The horizontal coordinates represent the slit direction of the streak camera 6, and the vertical coordinates represent the time direction of the streak camera 6. In image analysis software, after selecting the image, integration is performed along the time direction to obtain the integrated image. For example... Figure 3 The image shown is an integral plot of the stripe image output by the stripe camera 6. The horizontal axis represents time, and the vertical axis represents image intensity. Figure 3 The multiple peaks in the image represent multiple optical pulse trains, and the spacing between the peaks is the time delay Δt. From... Figure 3 From the integral curve, we can obtain the dynamic performance parameters of the stripe camera 6, such as the temporal resolution, full-screen time range, and dynamic range, at this scanning level.

Claims

1. A dynamic performance calibration system for the fast scan mode of a stripe camera, comprising a stripe camera, characterized in that: It also includes lasers, beam splitters, fast-response photodiodes, FP etalons, and readout cameras; The laser is used to output optical pulses; The beam splitter is located in the optical path of the laser output light pulse, and the light pulse is split into a first transmitted beam and a second reflected beam by the beam splitter; The FP etalon includes two parallel mirrors with a distance L between them; the two mirrors are located on the transmission optical path of the beam splitter to receive the first beam and output multiple light pulse trains with equal time intervals and progressively decreasing intensity; the streak camera is located on the output optical path of the FP etalon. The fast-response photodiode is located in the reflected light path of the beam splitter and is used to receive the second beam and output electrical pulses; the output terminal of the fast-response photodiode is connected to the trigger terminal of the stripe camera to trigger the stripe camera to work. The stripe camera receives light pulse trains and converts them into equidistant stripes, outputting a stripe image; 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 stripe camera. It is used to read stripe images through the image plane and convert them into digital signals, which are then transmitted to an external computer for analysis and calculation to obtain the calibration results of the dynamic performance of the stripe camera's fast scan mode. It also includes a first reflecting mirror; the first reflecting mirror is located in the reflected light path of the beam splitter; the fast-response photodiode is located in the reflected light path of the first reflecting mirror, and is used to receive the second beam and output electrical pulses; The stripe camera is in the picosecond to sub-picosecond range; The laser is a femtosecond laser that outputs light pulses with a time width of femtoseconds; It also includes a frosted glass, which is located between the FP etalon and the streak camera, to homogenize the light pulse train and broaden the light pulse train in the spatial direction.

2. The dynamic performance calibration system for the fast scan mode of a streak camera according to claim 1, characterized in that: The transmission-to-reflection ratio of the two mirrors of the FP etalon is 3:

7.

3. A method for dynamic performance calibration of a streak camera in fast scan mode, based on the dynamic performance calibration system for a streak camera in fast scan mode as described in any one of claims 1-2, characterized in that, This includes time resolution calibration, full-screen time calibration, and dynamic range calibration, specifically comprising the following steps: Step 1: Acquire the output image from the stripe camera. The laser emits light pulses which are split into a first beam and a second beam by a beam splitter. The first beam is transmitted through an FP etalon to generate multiple light pulse trains with equal time intervals and proportionally decreasing in intensity, which are then incident on the stripe camera. Simultaneously, the second beam is transmitted through a fast-response photodiode to generate electrical pulses, which trigger the stripe camera to operate. The stripe camera converts the received light pulse trains into equidistant stripes and outputs a stripe image. The readout camera acquires the stripe image output by the stripe camera. Step 2: Calibrate the dynamic performance of the stripe camera at the fast scan setting. The dynamic performance calibration of the fast scan mode of the stripe camera includes time resolution calibration, full-screen time calibration, and dynamic range calibration; A) Time resolution calibration: A1) The FP etalon generates multiple light 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 mirrors; A2) Analyzing the stripe image read by the readout camera, we find that the signal peak interval corresponding to the time interval Δt is N pixels, and the full width at half maximum (FWHM) of the narrowest light pulse train is n pixels. Therefore, the formula for calculating the temporal resolution τ of the stripe camera is: τ = (n / N)·Δt; The calibration of time resolution capability was completed; B) Full-screen time calibration: Full-screen time refers to the time range that the stripe camera can record; analyze the stripe image read by the readout camera, obtain the signal peak interval corresponding to the time interval Δt as N pixels; and obtain the full-screen time T of the stripe camera; T = (M / N)·Δt; 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 fringe camera. C) Dynamic range: After noise removal, the ratio of the maximum to the minimum brightness value of the image output by the streak camera is the dynamic range of the streak camera. The formula for calculating the dynamic range is: DR=(Imax-Inoise) / (Imin-Inoise); Where DR represents dynamic range, Imax represents maximum brightness, Inoise represents noise intensity, and Imin represents minimum brightness.

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