CN114046731B - Submicron single photon magnitude tiny light spot measuring method based on silicon photomultiplier - Google Patents

Abstract

The silicon photomultiplier tube-based submicron single-photon level micro-spot measurement method disclosed by the present invention uses a silicon photomultiplier tube as a single-photon response detector, combined with a precision displacement stage, through two-dimensional or one-dimensional space scanning and deconvolution Through calculation, the spatial distribution of the spot size and light intensity of the single-photon level pulsed laser spot focused by the microscope objective lens is obtained.

Description

Measurement method of submicron single-photon level micro-spot based on silicon photomultiplier tube

technical field

The invention belongs to the technical fields of optical measurement and semiconductor optoelectronics, and in particular relates to a method for measuring a submicron single-photon level tiny light spot based on a silicon photomultiplier tube.

Background technique

Micro-spot focusing technology has important applications in many fields. For example, laser self-collimation and measurement, optical information storage and transmission, and biological microfluidic tube preparation all need to focus the spot to a small size. Among them, the tiny spot of single-photon level has important applications in the fields of single-photon imaging, time-correlated fluorescence lifetime spectroscopy, and optical quantum information processing. At present, the commonly used measurement methods for tiny light spots include: flat panel/plane detector measurement method, (slit, knife edge, pinhole) scanning method, CCD (charge coupled device) method, etc. Jain A et al. (A.Jain, A.Panse, D.R.Bednarek, S.Rudin, Focal spotmeasurements using a digital flat panel detector, Spie Medical Imaging, 9033 (90335F) (2014)) use 194μm pixel flat panel detector (FPD, Flat panel detector) combined with micro pinhole (10μm) to measure the focal spot, using the deconvolution method to weaken the blurring effect brought by the detector during the focus spot measurement process, and the measurement spot size is about 0.6mm. TakeuchiA et al. (A.Takeuchi, Y.Suzuki, K.Uesugi, Differential-phase-contrast knife-edge scan method for precise evaluation of X-ray nanobeam, Japanese Journal of Applied Physics 54 (9) (2015) 092401.) for The micro-spot is improved on the basis of the knife-edge method. A hard x-ray micro-beam knife-edge scanning system with a CMOS sensor/CCD is used, and a tantalum film is used as the knife-edge to scan the focused micro-beam. The measured focus spot size is 25nm. However, this method cannot respond to single-photon-level pulsed spots. S K Tiwari et al (S.K.Tiwari, S.P.Ram, J.Jayabalan, S.R.Mishra, Measuring a narrow Bessel beam spot by scanning a charge-coupled device (CCD) pixel, Measurement Science and Technology 21(2)(2010)025308.) The CCD photosensitive surface is placed perpendicular to the beam axis, and the two-dimensional distribution of the beam intensity on the scanning plane is recorded by the CCD imaging method, and a 4 μm spot that is similar to the pixel size and smaller than the pixel size is measured. The CCD used in the above method does not have the ability to respond to single photons, and it is impossible to measure the pulse spot of the single photon level. At present, there are few reports on spot size measurement at the single-photon level. Liu Yuzhou et al. (Liu Yuzhou, Zhao Bin. Scanning method to measure the energy distribution of non-diffraction imaging micro-spots. Applied Optics, 06(2007):680-683.) used a photomultiplier tube (PMT) as an optical signal detector, and measured a 6μm The beam waist spot of the Bessel beam, but the PMT used in this method is a vacuum device, the minimum size is on the order of centimeters, which limits the integration of the system, and the photon number resolution is poor.

Contents of the invention

The purpose of the present invention is to provide a silicon photomultiplier tube-based measurement method for submicron single-photon-level micro-spots, which solves the problem that the prior art cannot realize the measurement of single-photon-level pulsed light spots.

The technical scheme adopted in the present invention is: a method for measuring submicron single-photon level micro-spots based on silicon photomultiplier tubes. The device based on the measurement method includes a nano-displacement stage for placing a silicon photomultiplier tube, and the nano-displacement stage is electrically connected in turn. Nano-stage driver and computer; under the nano-stage, there is a microscopic objective lens whose optical path faces the silicon photomultiplier tube, and a pinhole light-transmitting sheet and an inclined laser beam splitter are arranged in turn under the microscopic objective along the direction of the optical path. One side of the beam splitter is provided with a laser head along the direction of the optical path, and the laser head is electrically connected to a picosecond pulse laser driver; it also includes a stabilized power supply and a high-speed low-noise amplifier connected to the silicon photomultiplier tube, and the other part of the high-speed low-noise amplifier One end is connected to a digital oscilloscope, and the other end of the digital oscilloscope is connected to a computer; the measurement method specifically includes the following steps:

Step 1. Place the silicon photomultiplier tube in the electromagnetic shielding box, and place the photosensitive side down on the nano-shift stage;

Step 2. Horizontally place a pinhole light-transmitting sheet with a central hole on the optical path between the laser beam splitter and the microscope objective;

Step 3. The picosecond pulse laser driver makes the laser head irradiate the picosecond laser beam, which is split by the laser beam splitter and passed through the microscope objective lens to focus the picosecond laser beam on the surface of the silicon photomultiplier tube to form a spot;

Step 4. Supply power to the silicon photomultiplier tube through a regulated power supply to make it reach the Geiger avalanche mode. The output avalanche pulse signal is first amplified by a high-speed low-noise amplifier, and then input into a digital oscilloscope to obtain the pulse count rate;

Step 5, using a computer program to control the driver of the nano-displacement stage to move the nano-displacement stage to obtain the pulse count rate distribution at different positions;

Step 6. Use the pulse count rate distribution at different positions obtained on the computer and the shape function of the avalanche diode unit in the silicon photomultiplier tube to perform deconvolution operations, and perform Bessel function fitting on the results of the deconvolution operations to obtain the spot size information .

The present invention is also characterized in that,

In step 2, a pinhole with a diameter of no more than 100 microns is opened in the center of the pinhole light-transmitting sheet.

In step 3, the intensity of the picosecond laser beam is adjusted by a picosecond pulse laser driver, so that the count rate of the silicon photomultiplier tube avalanche is lower than 10% of the repetition frequency of the picosecond laser beam.

The picosecond laser beam has a repetition rate of 1-100 MHz.

In step 6, the spatial distribution function f(x, y) of the relative light intensity of the focused laser spot is obtained by deconvolution operation, which is expressed by formula (1):

f(x,y)=F ^-1 {F(f _x ,f _y )} (1)

In formula (1), x, y are the coordinates in the beam waist section perpendicular to the beam propagation direction, and F ^-1 {F(f _x , f _y )} is the inverse Fourier transform form of f(x, y) , F(f _x ,f _y ) is the Fourier transform form of f(x,y), which is expressed by formula (2):

F(f _x ,f _y )＝H(f _x ,f _y )/G(f _x ,f _y ) (2)

In formula (2), H(f _x , f _y ), G(f _x , f _y ) are expressed as follows through formulas (3) and (4) in turn:

In formula (3) and formula (4), L ₀ is the scanning space range, H(f _x , f _y ) is the Fourier transform form of pulse count rate distribution function h(x, y), G(f _x ,f _y ) is the Fourier transform form of the shape function g(x,y) of the avalanche diode unit, i is the imaginary unit, and e is the natural base.

The beneficial effects of the present invention are:

(1) Able to measure single-photon sub-micron light spots;

(2) It is easy to align the light spot with the detector without precise adjustment, and there is no need for optical slits/knife edges or pinholes. Using the tiny APD unit array in the SiPM, it can be scanned by fast movement and deconvolution operation. The spatial distribution information of the size and light intensity of the spot to be measured can be obtained;

(3) It has practical value in the detection of small and weak light spots and its related application fields.

Description of drawings

Fig. 1 is a schematic diagram of the device based on the silicon photomultiplier tube-based submicron single-photon level micro-spot measurement method of the present invention;

Fig. 2 is a schematic flow chart of a method for measuring a submicron single-photon level tiny spot based on a silicon photomultiplier tube in the present invention;

Figure 3a) is a one-dimensional distribution diagram of the pulse count rate measured by the present invention using the FBK SiPM (model: LF-HD) with a cell size of 35 μm;

Figure 3b) is a two-dimensional distribution diagram of the pulse count rate measured by the present invention using an NDL SiPM (model: EQR1011-1010C-T) with a cell size of 10 μm;

Figure 3c) is a one-dimensional distribution diagram of the pulse count rate measured by the present invention using a Hamamatsu SiPM (model: S12571-010C) with a cell size of 10 μm;

Figure 3d) is a two-dimensional distribution diagram of the pulse count rate measured by the present invention using the FBK SiPM (model: LF-HD) with a cell size of 35 μm;

Figure 3e) is a two-dimensional distribution diagram of the pulse count rate measured by the present invention using an NDL SiPM (model: EQR1011-1010C-T) with a cell size of 10 μm;

Figure 3f) The two-dimensional distribution diagram of the pulse count rate measured by the present invention using the Hamamatsu SiPM (model: S12571-010C) with a cell size of 10 μm;

Figure 4a) is a one-dimensional deconvolution result and a Bessel fitting diagram based on the FBK SiPM (model: LF-HD) with a cell size of 35 μm used in the present invention;

Figure 4b) is the one-dimensional deconvolution result and Bessel fitting diagram based on the NDL SiPM (EQR1011-1010C-T) with a cell size of 10 μm used in the present invention;

Fig. 4c) is a one-dimensional deconvolution result and a Bessel fitting diagram based on the present invention using a Hamamatsu SiPM (model: S12571-010C) with a cell size of 10 μm.

In the figure, 1. Stabilized power supply, 2. High-speed low-noise amplifier, 3. Digital oscilloscope, 4. Nano-stage driver, 5. Nano-stage, 6. Picosecond pulse laser driver, 7. Laser head, 8. Laser Beam splitter, 9. pinhole light-transmitting sheet, 10. microscope objective lens, 11. silicon photomultiplier tube, 12. computer.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

The present invention provides a method for measuring submicron single-photon level micro-spots based on silicon photomultiplier tubes. The device based on it is shown in FIG. Electrically connected to the nano-displacement stage driver 4 and computer 12; the nano-displacement stage 5 is provided with a microscopic objective lens 10 with an optical path facing the silicon photomultiplier tube 11, and a pinhole light-transmitting sheet is respectively arranged under the microscopic objective lens 10 along the optical path direction 9 and an inclined laser beam splitter 8, one side of the laser beam splitter 8 is provided with a 375 nm laser head 7 along the optical path direction, and the laser head 7 is electrically connected with a picosecond pulse laser driver 6; 11 is connected to a stabilized power supply 1 and a high-speed low-noise amplifier 2, the other end of the high-speed low-noise amplifier 2 is connected to a digital oscilloscope 3, and the other end of the digital oscilloscope 3 is connected to a computer 12; the measurement method specifically includes the following steps, as shown in Figure 2 Shown:

Step 1, silicon photomultiplier tube 11 is placed in an electromagnetic shielding box, and the photosensitive surface is installed on the piezoelectric ceramic (PZT) nano-displacement stage 5 downwards, and is used for controlling the position of silicon photomultiplier tube 11; Silicon photomultiplier tube 11 is composed of a tiny avalanche photodiode (APD) unit array, with gaps between APD units, and a square APD corresponds to a square wave function or a rectangular function. The photosensitive area of the silicon photomultiplier tube 11 is above a millimeter square, much larger than a single photon Avalanche Photodiode (SPAD), so alignment of spot to detector is easy and no optical slit/knife edge or pinhole is required in front of the detector.

Among them, the silicon photomultiplier tube 11 used in the measurement is selected as FBK SiPM (LF-HD, produced in Italy), NDLSiPM (EQR1011-1010C-T, produced in China), Hamamatsu SiPM (S12571-010C, produced in Hamamatsu, Japan), and the unit The dimensions are 35×35μm ² (FBK), 10×10μm ² (NDL), 10×10μm ² (Hamamatsu); the piezoelectric ceramic (PZT) nano-stage is Pinano XYZ (closed-loop displacement accuracy 2nm; displacement range 200μm, German Domestic)

Step 2. Horizontally place a pinhole light-transmitting sheet 9 with a central hole on the optical path between the laser beam splitter 8 and the silicon photomultiplier tube 11. The center of the pinhole light-transmitting sheet 9 is provided with a pinhole with an aperture of 100 μm. to reduce the diameter of the spot;

Step 3, the picosecond pulse laser driver 6 causes the laser head 7 to emit a picosecond pulse laser beam, which is split by the laser beam splitter 8 and passes through the pinhole light-transmitting sheet 9 and the microscopic objective lens 10 to make the picosecond pulse laser beam flow through the silicon photoelectric The surface focusing of the multiplier tube 11; the specific processing method is as follows:

The intensity of the laser light generated by the laser head 7 is adjusted by the picosecond pulse laser driver 6, so that the count rate of the avalanche of the silicon photomultiplier tube 11 is lower than 10% of the repetition frequency of the picosecond pulse laser driver 6, so as to ensure that the pulse photons reaching the SiPM photosensitive surface decays to the single photon level.

Wherein the microscope (including microscopic objective lens 10, pinhole light-transmitting film 9, and laser beam splitter 8) is X-73, Olympus Corp. (nominal value of objective lens resolution is 0.42 μm, produced by Olympus Corporation of Japan); picosecond The laser beam is PDL-800D375 (central wavelength, 375nm; full width at half maximum, 44ps; repetition rate, 31.125kHz–80MHz; maximum average light energy, 0.7mW; produced by PicoQuant, Germany).

Step 4. Supply power to the silicon photomultiplier tube 11 through the programmable regulated power supply 1 to make it reach the Geiger avalanche mode. The output avalanche pulse signal is first amplified by the high-speed low-noise amplifier 2, and then input into the digital oscilloscope 3 for observation Avalanche pulse waveform, get the pulse count rate;

Among them, the regulated power supply 1 is IT6235 precision regulated power supply (domestic), which is used to provide power supply.

Step 5, use the LABVIEW program control displacement stage driver 4 in the computer 12 to make the nanometer displacement stage 5 move, set the equivalent photon number threshold value of the digital oscilloscope 3 at 0.5p.e., display and record the avalanche pulse signal of the trigger through the digital oscilloscope 3 The pulse counting frequency is collected by the computer 12, and the pulse counting frequency is output on the computer 12, which is the one-dimensional and two-dimensional spatial distribution of the relative photoresponsivity;

Step 6, the one-dimensional spatial distribution of the pulse count rate collected by the computer 12 is used in the LABVIEW program terminal to perform a deconvolution operation using the deconvolution module and the shape function (rectangular function) of the APD unit, and the deconvolution result is imported into the computer 12 The built-in general mathematics software uses Bessel function fitting to get the spot size information.

In the experiments performed on different types of silicon photomultiplier tubes 11 at different times in steps 3 and 4, it is necessary to adjust the distance of the SiPM relative to the objective lens, and perform multiple measurements to screen the one-dimensional spatial distribution of the pulse count rate and perform the peak-to-valley ratio to ensure that the spot in the best focus position.

The principle of the method for measuring the submicron single-photon level tiny spot based on the silicon photomultiplier tube of the present invention is as follows:

The laser light generated by the picosecond pulse laser driver 6 and the laser head 7 is irradiated onto the silicon photomultiplier tube 11 fixed on the nanometer displacement stage 5 through the laser beam splitter 8 and the pinhole light-transmitting sheet 9, and the regulated power supply 1 supplies the silicon photoelectric The multiplier tube 11 supplies power, and the output avalanche pulse signal is first amplified by the high-speed low-noise amplifier 2, the waveform and the spatial distribution of the relative photon response of the detector are observed by a digital oscilloscope, and the computer 12 collects the one-dimensional sum of the relative photon responsivity generated by the avalanche. For two-dimensional spatial distribution, use the deconvolution module and rectangular function to perform deconvolution operations on the LABVIEW program. The operation principle is as follows:

The relationship between relative spatial responsivity distribution data h(x, y), rectangular function g(x, y), and spot light intensity spatial distribution function f(x, y) can be given by formula (1):

f(x,y)*g(x,y)+ε(x,y)=h(x,y) (1)

In formula (1), x and y are the coordinates in the beam waist section perpendicular to the beam propagation direction, ε is the noise fluctuation of the measurement signal, which can be eliminated by low-pass filtering operation, and the intensity distribution function f( x,y). The Fourier transform of h(x, y) and g(x, y) is given by (2) and (3):

In formula (2) (3), L ₀ is the scanning space range.

F(f _x ,f _y )＝H(f _x ,f _y )/G(f _x ,f _y ) (4)

where F(f _x ,f _y ) is the Fourier transform of f(x,y). Then the spatial distribution function f(x,y) of the relative light intensity of the focused laser spot is obtained by inverse Fourier transform:

f(x,y)=F ^-1 {F(f _x ,f _y )} (5)

Finally, the general mathematical software embedded in the computer 12 is used to perform Bessel function fitting on the light spot deconvolution result, and the one-dimensional distribution map of the light spot is drawn using the drawing software.

Example

As shown in Figure 1, the silicon photomultiplier tube 11 models adopted in the present embodiment are respectively selected from FBK (LF-HD, produced in Italy), NDL (EQR1011-1010C-T, produced in China) Hamamatsu S12571-010C (produced in Japan); The nano-shift stage 5 is nanoXYZ (no-load resolution 2nm; displacement range, 200 microns, made in Germany); microscope (including microscope objective lens 10 (model HAS-Y-2-40, bandwidth 10kHz-1.9GHz, noise factor 4.9dB , voltage gain 40dB (100×), made in Germany), pinhole light-transmitting sheet 9, laser beam splitter 8) is X-73, Olympus Corp., (produced by Olympus Corporation in Japan); the picosecond pulse laser is PDL-800D375 (center wavelength, 375nm; full width at half maximum, 44ps; repetition rate, 31.125kHz–80MHz; maximum average light energy, 0.7mW; made in Germany); digital oscilloscope 4 is DPO4102B-L for digital phosphor oscilloscope (sampling rate 5GSa /s, 1GHz bandwidth, produced by Tektronix in the United States);

The working principle of this embodiment is:

The silicon photomultiplier tube 11 detector is fixed on the nano-shift stage 5, and the silicon photomultiplier tube 11 can follow the nano-shift stage 5 to move in two directions of X and Y according to a certain step. The programmable regulated power supply 1 is used to bias the silicon photomultiplier tube 11 to reach the state of Geiger avalanche breakdown. The avalanche signal generated by the avalanche breakdown of the silicon photomultiplier tube 11 is amplified by the high-speed low-noise amplifier 2 and then transmitted to the high-speed Digital oscilloscope 3 to obtain the avalanche pulse count rate at 0.5p.e. Set the appropriate step length on the PC side, the silicon photomultiplier tube 11 fixed by the nano-shift stage 2 moves point by point along the X/Y direction, and simultaneously measure and record the pulse count rate displayed by the digital oscilloscope 3 on each position point, you can get 0.5p.e. The next-dimensional pulse count rate, the avalanche pulse count rate distribution obtained by formula (4) (5) is deconvolved with the rectangular function, and the spot information distribution can be obtained. Fig. 3a) to Fig. 3f) are distribution diagrams of one-dimensional pulse count rate and two-dimensional pulse count rate of silicon photomultiplier tube 11 of different sizes, as can be seen from Fig. 3d) to Fig. 3f): the relative photoresponse space inside the APD unit The distribution is uniform, and different APD units can be clearly distinguished. From 3d) the size of the Gap (interval) region between the APD units of FBK 35μm SiPM is 5μm, so it can be concluded that the size of the spot (FWHM) is significantly smaller than 5μm, if the spot size is larger than 5μm, different APD units will not be able to distinguish. Figure 3e) is the one-dimensional/two-dimensional distribution diagram of the relative photoresponse space of NDL10μm SiPM, in which the period of the APD unit is 10μm, the size of the photosensitive area is 7μm, and the size of the gap is 3μm. 3μm is still small. From Figure 3f), the details inside the APD unit in the 10μm Hamamatsu SiPM can still be resolved, indicating that the FWHM of the spot size should be less than 1μm. Figure 3a) to Figure 3c) and square wave matrix deconvolution operation, Figure 4a) to Figure 4c) are deconvolution results and Bessel fitting diagrams, the obtained spot size is about 0.66μm.

Claims (4)

1. The submicron single photon magnitude tiny light spot measuring method based on the silicon photomultiplier is characterized in that a device based on the measuring method comprises a nanometer displacement table (5) for placing a silicon photomultiplier (11), wherein the nanometer displacement table (5) is sequentially and electrically connected with a nanometer displacement table driver (4) and a computer (12); a microscope objective (10) with a light path right facing a silicon photomultiplier (11) is arranged below the nanometer displacement table (5), a pinhole light-transmitting sheet (9) and an inclined laser beam splitter (8) are sequentially arranged below the microscope objective (10) along the light path direction, a laser head (7) is arranged on one side of the laser beam splitter (8) along the light path direction, and the laser head (7) is electrically connected with a picosecond pulse laser driver (6); the device is characterized by also comprising a stabilized voltage power supply (1) and a high-speed low-noise amplifier (2) which are both connected with the silicon photomultiplier (11), wherein the other end of the high-speed low-noise amplifier (2) is connected with a digital oscilloscope (3), and the other end of the digital oscilloscope (3) is connected to a computer (12); the measuring method specifically comprises the following steps:

step 1, placing a silicon photomultiplier (11) in an electromagnetic shielding box, and placing the silicon photomultiplier on a nanometer displacement table (5) with a photosensitive surface facing downwards;

step 2, horizontally placing a pinhole light-transmitting sheet (9) with a central hole on a light path between a laser beam splitter (8) and a microscope objective (10);

step 3, enabling a laser head (7) to irradiate picosecond laser beams by a picosecond pulse laser driver (6), splitting the picosecond laser beams by a laser beam splitter (8), and enabling the picosecond laser beams to be focused into light spots on the surface of a silicon photomultiplier (11) through a microscope objective (10);

step 4, supplying power to the silicon photomultiplier (11) through a voltage-stabilized power supply (1) to enable the silicon photomultiplier to reach a Geiger avalanche mode, amplifying an output avalanche pulse signal through a high-speed low-noise amplifier (2), and inputting the avalanche pulse signal into a digital oscilloscope (3) to obtain a pulse counting rate;

step 5, controlling a driver (4) of the nano displacement table by using a program of a computer (12) to move the nano displacement table (5) and acquiring pulse counting rate distribution at different positions;

step 6, performing deconvolution operation by using pulse counting rate distribution at different positions acquired by the computer (12) and a shape function of an avalanche diode unit in the silicon photomultiplier (11), and performing Bessel function fitting on a deconvolution operation result to obtain light spot size information; the spatial distribution function f (x, y) of the relative light intensity of the focused laser spot is obtained by deconvolution operation, and is expressed by a formula (1):

f(x,y)＝F ^-1 {F(f _x ,f _y )} (1)

in the formula (1), x and y are beam waist sections perpendicular to the beam propagation directionIn-plane coordinates, F ^-1 {F(f _x ,f _y ) Is the inverse Fourier transform of F (x, y), F (F) _x ,f _y ) Is a fourier transform form of f (x, y) and is represented by equation (2) as:

F(f _x ,f _y )＝H(f _x ,f _y )/G(f _x ,f _y ) (2)

in the formula (2), H (f) _x ,f _y )、G(f _x ,f _y ) Expressed sequentially by equations (3), (4) as:

in the formulae (3) and (4), L ₀ For the spatial extent of the scan, H (f) _x ,f _y ) In the form of a Fourier transform of the pulse count rate distribution function h (x, y), G (f) _x ,f _y ) In the form of a fourier transform of the shape function g (x, y) of the avalanche diode cell, i is in imaginary units and e is a natural base.

2. The method for measuring the submicron single photon magnitude micro light spot based on the silicon photomultiplier as claimed in claim 1, wherein a pinhole having a pore size not more than 100 μm is formed in the center of the pinhole light-transmitting sheet (9) in the step 2.

3. The method for measuring the submicron single photon magnitude micro light spot based on the silicon photomultiplier as claimed in claim 1, wherein the step 3 adjusts the intensity of the picosecond laser beam through the picosecond pulse laser driver (6) to make the avalanche count rate of the silicon photomultiplier (11) less than 10% of the repetition rate of the picosecond laser beam.

4. The silicon photomultiplier-based submicron single photon magnitude micro spot measurement method according to claim 3, wherein the repetition frequency of the picosecond laser beam is 1-100 megahertz.

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