CN115389017B - A pulse laser power measurement method based on integration circuit - Google Patents

Abstract

The invention provides a pulse laser power measuring method based on an integrating circuit, which is suitable for the conditions of low data sampling frequency and no synchronous trigger signal, and solves the problems of harsh measuring conditions and low measuring precision of the existing pulse laser power measuring method. The measuring method is characterized in that a typical RC integral circuit is utilized to carry out signal conditioning amplification on a voltage signal generated by a pulse laser irradiation photoelectric detector, an analog-digital converter is utilized to carry out equidistant sampling on the amplified voltage signal, the back-pushing calculation is carried out according to the characteristics of the integral circuit and a laser power analysis expression, when the back-pushing calculation result meets the error, the light emitting zero moment of the pulse laser can be determined, and the pulse laser power to be measured is further calculated.

Description

A pulse laser power measurement method based on integration circuit

Technical Field

The invention relates to the field of pulse laser power measurement, and in particular to a pulse laser power measurement method based on an integration circuit.

Background technique

Photodetectors have the characteristic of converting optical signals into electrical signals and are widely used in the detection of laser power. For continuous laser signals, photodetectors can sample and monitor the laser power according to the set sampling frequency. For pulsed laser signals, there are usually two ways to measure using photodetectors: one is the direct measurement method, which is to sample at a higher frequency to ensure that there are enough sampling points within the pulse width range, and each sampling directly obtains the laser signal power at the sampling moment; the other is the integral calculation method, which is to use an integral circuit to integrate the signal within the pulse width, and calculate the average power of the pulsed laser signal by back-calculation. The direct measurement method is simple and convenient, but it has high requirements on the sampling frequency, and the measurement accuracy of the average power of the pulsed laser is affected by the number of sampling points. There is also the problem of too much invalid data when measuring low duty cycle pulsed laser signals. The integral calculation method can obtain a complete pulse signal, but the measurement accuracy of the signal zero point directly affects the calculation result, and usually requires the introduction of a synchronous trigger mechanism.

In practical applications, the sampling frequency may be difficult to meet the requirements of the direct measurement method due to the limitations of the data acquisition equipment or transmission channel performance. When the integral calculation method is used for non-cooperative measurement at a lower sampling frequency, the signal zero point measurement accuracy is low due to the lack of a synchronous trigger mechanism, which will lead to large errors in the calculation results.

Summary of the invention

The purpose of the present invention is to solve the problems of harsh measurement conditions and low measurement accuracy in existing pulse laser power measurement methods, and to provide a pulse laser power measurement method based on an integration circuit, which is suitable for conditions where the data sampling frequency is low and there is no synchronous trigger signal.

In order to achieve the above object, the technical solution adopted by the present invention is:

A pulse laser power measurement method based on an integration circuit is special in that it includes the following steps:

Step 1: Build an RC integration circuit to condition and amplify the voltage signal generated by the pulsed laser irradiated photodetector and convert it into a digital voltage signal;

Step 2: Perform time-series sampling on the digital voltage signal output by the RC integration circuit at a sampling interval of _ts . According to the amplitude of the voltage signal obtained by sampling, preliminarily draw a curve of the change of the amplitude of the voltage signal output by the RC integration circuit within the single pulse irradiation time. Mark the sampling point with the largest amplitude of the voltage signal in the sampling data as the nth sampling point; n is an integer greater than or equal to 3.

The sampling interval satisfies: 0<t _s <0.5t _w , where t _w is the pulse width to be measured;

Step 3, calculate and obtain the laser power value of the charging section of the RC integration circuit;

3.1. Define the zero time of pulse laser emission t _start as time 0 on the time axis, then the time region corresponding to the n-1th sampling point is [t _w -2t _s ,t _w ], and the corresponding voltage signal amplitude is V _n-1 ;

3.2. Divide the time region [ _tw - _2ts , _tw ] into m segments on average. Then the values of m+1 time points in the corresponding time region are tw _{- 2ts} +( _2ts /m)*j, j=0, 1, 2, ...m, and the corresponding voltage signal amplitudes are all Vn _-1 ; m is an integer greater than or equal to 1;

3.3. Substitute the voltage signal amplitude Vn _-1 and the m+1 time point values into the analytical expression of laser power in the charging stage P=f(R,C,V,t), and calculate the laser power value P(j) sequence corresponding to the m+1 time point values in the charging stage;

Step 4, calculate and obtain the laser power value of the discharge section of the RC integration circuit;

4.1. According to the setting of the sampling interval, the time region corresponding to the n+1th sampling point is [t _w ,t _w +2t _s ], and the corresponding voltage signal amplitude is V _n+1 ;

4.2. Divide the time region [ _tw , _tw + _2ts ] into m segments evenly. The values of m+1 time points in the corresponding time region are _tw +( _2ts /m)*j, and the corresponding voltage signal amplitudes are all Vn ₊₁ ;

4.3. Substitute the voltage signal amplitude Vn ₊₁ and the m+1 time point values into the discharge segment laser power analytical expression P′＝g(R,C,V,t), and calculate the laser power value P′(j) sequence corresponding to the m+1 time point values of the discharge segment;

Step 5, sequentially calculate the absolute value of the difference between the laser power values corresponding to the m+1 time points of the charging section and the discharging section ε _j =|P(j)-P′(j)|, and obtain j _right corresponding to the minimum value of ε _j ;

Step 6, calculating the power value of the pulsed laser to be measured;

The j _right calculation time point corresponding to the minimum value of ε _j and its corresponding voltage signal amplitude are used to calculate the power value of the pulsed laser to be measured through the analytical expression of laser power.

Furthermore, step 6 is specifically as follows:

Using the analytical expression of laser power in the charging stage P=f(R,C,V,t), the time point value is calculated as _tw - _2ts +( _2ts /m)* _jright , the voltage signal amplitude is Vn _-1 , and the power value _Pright of the pulse laser to be measured is calculated;

Alternatively, using the discharge laser power analytical expression P′=g(R,C,V,t), the time point value is calculated as t _w +(2t _s /m)*j _right , the voltage signal amplitude is V _n+1 , and the power value P′ _right of the pulse laser to be measured is calculated.

Furthermore, in step 1, the photodetector is a single photodetector or a photodetector array.

Furthermore, when the photodetector is a photodetector array, each photodetector performs time-series sampling on the digital voltage signal output by the RC integration circuit at the same sampling interval _ts .

Furthermore, when the photodetector array includes N photodetectors, N is an integer greater than or equal to 2, step 5 is specifically:

5.1. Calculate the absolute value of the difference between the laser power values corresponding to the m+1 time points of the charging and discharging segments of the k-th photodetector, ε _j (k) = |P(j,k)-P′(j,k)|, and obtain the j _right (k) sequence value corresponding to the minimum value of ε _j (k), k = 1, 2, 3, ..., N;

5.2. Calculate the average value of the j _right (k) sequence value The j _right corresponding to the minimum value of ε _j .

Furthermore, in step 5, when the minimum value of ε _j is greater than the measurement accuracy given by the measuring device, a value greater than the initial value of m is selected to re-divide the time region, and steps 3 to 5 are repeated until the minimum value of ε _j meets the measurement accuracy.

Furthermore, in step 3, the initial value of m is 100.

Compared with the prior art, the present invention has the following beneficial technical effects:

1. The pulse laser power measurement method based on the integration circuit provided by the present invention realizes the measurement of the pulse laser power using the integration circuit under the condition of no synchronization signal. The measurement accuracy of the non-ideal square wave pulse signal is much better than the direct measurement method under the same sampling frequency. While retaining the advantage of the integral calculation method in fully recording the pulse signal, it overcomes the limitation of the conventional integral calculation method that relies on the synchronization signal, and expands the application scenarios of the integral calculation method.

2. The measurement method of the present invention is suitable for the scenario where a photoelectric detector array using an integral calculation method measures the power density distribution of a pulsed laser spot. By counting the laser emission time calculated by each array detector and taking the average value, the calculation error of the laser emission time can be reduced and the measurement accuracy can be improved.

3. The analytical model for calculating the sampling time in the present invention is applicable to the determination of the signal starting point (zero point) in the sampling signal of other integration circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of an integration circuit for measuring pulsed laser power;

FIG2 is a schematic diagram of a typical output voltage variation curve of an integrator circuit;

FIG3 is a timing diagram of a sampling signal and a pulse signal in an embodiment of the present invention;

FIG4 is a schematic diagram of an area where a sampling point may be located when a signal zero point is not determined in an embodiment of the present invention;

FIG. 5 is a schematic diagram of a valid data segment of a sampling signal according to an embodiment of the present invention.

Detailed ways

In order to make the purpose, advantages and features of the present invention clearer, the pulse laser power measurement method based on the integration circuit proposed by the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood by those skilled in the art that these implementations are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

The basic principle of the present invention is: for the voltage signal generated by the pulse laser irradiation photodetector, the RC integration circuit (as shown in Figure 1) is first used to condition and amplify the signal, and then the analog-to-digital converter (ADC) is used to convert it into a digital signal, the amplified voltage signal is collected at equal intervals, and finally the average power of the pulse laser is back-calculated based on the characteristics of the RC integration circuit.

The voltage change curve formed during the measurement process can be divided into two sections (as shown in Figure 2): one is the charging section curve during pulse laser irradiation, also called the rising section; the other is the discharge section curve after irradiation, also called the falling section. The charging section and the discharge section each have their own analytical expressions or approximate analytical expressions. Assume that the laser power value of the charging section P = f(R, C, V, t), and the laser power value of the discharge section P′ = g(R, C, V, t), where t is the time relative to the zero time t _start of the pulse laser emission, and V is the voltage signal amplitude output by the RC integration circuit at time t. It is usually assumed that the power curve of the entire pulse section is a square wave, a triangle wave or other waveform with a known shape. The curve function corresponding to each waveform is different, which mainly depends on the values of R and C.

For an integration circuit that determines RC parameters and waveform shape, there are only two variables in the analytical expressions of the charging and discharging stages: the voltage value of the sampling point and the sampling time value relative to the start time of the pulse laser (signal zero point t _start ). The voltage value and sampling time value of the sampling point can be directly obtained by data acquisition, but when there is no synchronization signal, the signal zero point value may be any time between the initial signal point and the adjacent baseline sampling point (as shown in Figure 3).

It can be seen from the characteristics of the integral circuit that if the signal zero point value is correct, the laser power value can be obtained according to a voltage V value in the charging section or the discharging section, and the laser power value calculated by back-calculating using the analytical expression at a sampling point in the charging section and the discharging section should be equal. Therefore, after taking a known voltage V value sampling point in the charging section and the discharging section of Figure 2, several signal zero point values can be selected in the interval where the sampling point is located for back-calculation and comparison of the calculation results, and the corresponding signal zero point value when the back-calculation results of each sampling point are consistent can be found, and it can be determined as the correct value of the signal zero point. That is, as long as the signal zero point is determined, the laser power value can be calculated regardless of the V in the charging section or the discharging section.

The pulse laser power measurement method based on the integration circuit proposed in the present invention specifically comprises the following steps:

Step 1: Build an RC integration circuit to condition and amplify the voltage signal generated by the pulsed laser irradiated photodetector;

The photodetector is a single photodetector or a photodetector array, and each detector in the photodetector array has the same sampling timing;

Step 2: Perform time-series sampling on the voltage signal output by the RC integration circuit at a certain sampling interval _ts . According to the amplitude of the voltage signal obtained by sampling, preliminarily draw a curve of the change of the amplitude of the voltage signal output by the RC integration circuit within the single pulse irradiation time (as shown in FIG3 ). The sampling point with the largest voltage signal amplitude in the sampling data is marked as the nth sampling point, and its corresponding voltage signal amplitude is V _max ; n is an integer greater than or equal to 3;

The pulse width to be measured is t _w , and the sampling interval is 0<t _s <0.5t _w . Sampling is performed at this sampling interval, which can ensure that the charging section during the pulse laser irradiation period has at least 3 sampling points.

Figure 3 shows the timing diagram of the sampling interval and the pulse signal. Figures 4 and 5 respectively show schematic diagrams of the possible areas where the sampling points may be located when the signal zero point is not determined. It can be seen that the nth sampling point with the largest voltage signal amplitude V _max may be located in the charging section or the discharging section. Since the sampling interval 0<t _s <0.5t _w , it can be guaranteed that the n-1th sampling point must be in the charging section and the n+1th sampling point must be in the discharging section. The time region corresponding to the n-1th sampling point is [t _w -t _s ,t _w +t _s ].

Step 3: Calculate and obtain the laser power value of the charging section of the RC integration circuit

3.1. Assuming that the zero time of pulse laser emission t _start is the time 0 on the time axis, the time region corresponding to the n-1th sampling point is [t _w -2t _s ,t _w ], and the corresponding voltage signal amplitude is V _n-1 ;

3.2. Divide the time region [ _tw - _2ts , _tw ] into m segments on average. Then the values of m+1 time points in the corresponding time region are tw _{- 2ts} +( _2ts /m)*j, j=0, 1, 2, ...m, and the corresponding voltage signal amplitudes are all Vn _-1 ; m is an integer greater than or equal to 1;

3.3. Substitute the voltage signal amplitude Vn _-1 and the m+1 time point values into the analytical expression of the laser power in the charging section P=f(R,C,V,t), and calculate the laser power value P(j) sequence corresponding to the m+1 time point values in the charging section.

Step 3: Calculate and obtain the laser power value of the discharge section of the RC integrator circuit

4.1. According to the setting of the sampling interval, the time region corresponding to the n+1th sampling point is [t _w ,t _w +2t _s ], and the corresponding voltage signal amplitude is V _n+1 ;

4.2. Divide the time region [ _tw , _tw + _2ts ] into m segments evenly. The values of the m+1 time points in the corresponding time region are _tw +( _2ts /m)*j, and the corresponding voltage signal amplitudes are all Vn ₊₁ ;

4.3. Substitute the voltage signal amplitude Vn ₊₁ and the m+1 time point values into the discharge segment laser power analytical expression P′=g(R,C,V,t), and calculate the laser power value P′(j) sequence corresponding to the m+1 time point values of the discharge segment.

Step 5, calculate the absolute value of the difference between the laser power values corresponding to the m+1 time points of the charging section and the discharging section ε _j =|P(j)-P′(j)| in sequence, and obtain j _right corresponding to the minimum value of ε _j .

According to the above principle, when the zero time t _start of the pulse laser emission is determined, the laser power values calculated at any time in the charging section and the discharging section are equal or have a small difference. Therefore, when ε _j is the smallest, it is considered that the zero time t _start of the pulse laser emission is determined, and the pulse laser power value calculated at the corresponding time point value of j _right is accurate.

Step 6: Calculate the power value of the pulsed laser to be measured

Using the analytical expression of laser power in the charging stage P=f(R,C,V,t), the time point value is calculated as _tw - _2ts +( _2ts /m)* _jright , the voltage signal amplitude is Vn _-1 , and the power value _Pright of the pulse laser to be measured is calculated;

Alternatively, using the discharge laser power analytical expression P′=g(R,C,V,t), the time point value is calculated as t _w +(2t _s /m)*j _right , the voltage signal amplitude is V _n+1 , and the power value P′ _right of the pulse laser to be measured is calculated.

have to be aware of is:

First, using the above-mentioned pulse laser power measurement method, when the ε _j value calculated in step 5 is greater than the measurement accuracy given by the measuring device, a higher division accuracy (i.e., a larger m value) is selected to re-divide the time area, and steps 3 to 5 are repeated to obtain a more accurate time point value calculation, so as to improve the accuracy of the measured power value of the pulsed laser to be measured.

The value of m should take into account both calculation accuracy and efficiency. Usually the initial value of m is 100.

Secondly, when the photodetector array is used to detect the light spot in step 1, each detector in the array has the same sampling timing. All detectors irradiated by the laser are counted, and the j _right corresponding to the minimum value of the sampling time value ε _j of each detector is calculated. Then the average value of all j _right is taken to calculate the laser power, thereby reducing the calculation error.

The sampling moments calculated by all the detectors irradiated by the laser can be aligned with the selected reference detector, and the average value can be taken to reduce the calculation error.

A specific embodiment is given below:

For example, when the pulse width of the pulse signal to be measured is 3ms, the sampling frequency of the sampling point is 1kHz, that is, the time interval between two adjacent data points is 1ms, then there are at least 3 sampling points within the 3ms (charging period) of the pulse action.

The first data point with signal in the data segment before and after the marker pulse is k+1, and the previous point is k, and the subsequent points are k+2, k+3, k+4, ... According to the signal characteristics, the peak point of the sampled data may be k+3 or k+4. Assuming that the pulse starts at zero, the signal peak time is 3ms, then the peak point of the sampled data, whether it is k+3 or k+4, will be within the range of [2ms, 4ms].

Because the peak point of the sampled data cannot be determined whether it is in the charging stage or the discharging stage, but the previous point must be in the charging stage, and the next point must be in the discharging stage. Assuming that the peak point of the sampled data is the k+3th point, the k+2th point is taken as the calculation point of the charging stage, and the interval corresponding to its sampling time is one sampling time interval earlier than the peak point of the sampled data, that is, 1ms, that is, the possible interval of the sampling time is [1ms, 3ms]. The required calculation accuracy is set to 0.1ms, and the sequence value of the sampling time in this interval is: 1.0ms, 1.1ms, 1.2ms, ..., 3.0ms. Substitute this sequence value and the sampled data value _V2 of the k+2th point into the analytical expression P(t) = f(R,C,V,t) of the laser power back-test of the RC integration circuit charging stage, and calculate the sequence value P of the laser power to be measured.

Similarly, when the peak point of the sampling data is the k+3th point, the k+4th point is taken as the calculation point of the discharge segment. The RC integration circuit is used to back-calculate the analytical expression P′(t)=g(R,C,V,t) of the laser power in the discharge segment to obtain the laser power sequence value P′ to be measured.

The absolute value of the difference between the laser power sequence values P and P′ is calculated in sequence, wherein the laser power P or P′ corresponding to the time point when the absolute value of the difference is the smallest is the laser power value to be measured.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims (7)

1. The pulse laser power measuring method based on the integrating circuit is characterized by comprising the following steps of:

step 1, constructing an RC integrating circuit to perform signal conditioning amplification on a voltage signal generated by a pulse laser irradiation photoelectric detector and convert the voltage signal into a digital voltage signal;

Step 2, carrying out time sequence sampling on the digital voltage signal output by the RC integrating circuit at a sampling interval t _s, preliminarily drawing a voltage signal amplitude change curve output by the RC integrating circuit in single pulse irradiation time according to the amplitude of the voltage signal obtained by sampling, and marking a sampling point with the maximum voltage signal amplitude in sampling data as an nth sampling point; n is an integer of 3 or more;

The sampling interval satisfies: 0<t _s<0.5t_w, wherein t _w is the pulse width to be measured;

step 3, calculating and obtaining the laser power value of the charging section of the RC integral circuit;

3.1, defining the time t _start when the pulse laser emits light as 0 moment on a time axis, wherein the time region corresponding to the n-1 sampling point is [ t _w-2t_s,t_w ], and the corresponding voltage signal amplitude is V _n-1;

3.2, dividing the time region [ t _w-2t_s,t_w ] into m segments on average, wherein m+1 time point values in the corresponding time region are t _w-2t_s+(2t_s/m) j, j=0, 1,2, … m, and the corresponding voltage signal amplitudes are V _n-1; m is an integer greater than or equal to 1;

3.3, substituting the voltage signal amplitude V _n-1 and m+1 time point values into a laser power analysis expression P=f (R, C, V, t) of the charging section, and calculating to obtain a laser power value P (j) sequence corresponding to the m+1 time point values of the charging section; wherein t is the time t _start relative to the time when the pulse laser emits light, and V is the amplitude of the voltage signal output by the RC integrating circuit at the time t;

step 4, calculating and obtaining the laser power value of the discharge section of the RC integral circuit;

4.1, according to the setting of the sampling interval, the time area corresponding to the (n+1) th sampling point is [ t _w,t_w+2t_s ], and the corresponding voltage signal amplitude is V _n+1;

4.2, dividing the time region [ t _w,t_w+2t_s ] into m sections averagely, wherein m+1 time point values in the corresponding time region are t _w+(2t_s/m) x j respectively, and the corresponding voltage signal amplitudes are V _n+1;

4.3, substituting the voltage signal amplitude V _n+1 and m+1 time point values into a discharge segment laser power analysis expression P '=g (R, C, V, t), and calculating to obtain a laser power value P' (j) sequence corresponding to the m+1 time point values of the discharge segment;

Step 5, sequentially calculating absolute values epsilon _j = |P (j) -P' (j) | of differences between laser power values corresponding to m+1 time point values of the charging section and the discharging section, and obtaining j _right corresponding to the minimum value of epsilon _j;

step 6, calculating the power value of the pulse laser to be measured;

And calculating a time point and a voltage signal amplitude corresponding to the time point by using j _right corresponding to the minimum value of epsilon _j, and calculating the power value of the pulse laser to be detected by using a laser power analysis expression.

2. The method for measuring pulse laser power based on the integrating circuit according to claim 1, wherein the step 6 is specifically:

Calculating a time point value t _w-2t_s+(2t_s/m)*j_right and a voltage signal amplitude value V _n-1 by using a charging section laser power analysis expression P=f (R, C, V and t), and calculating to obtain a power value P _right of the pulse laser to be detected;

or calculating the power value P '_right of the pulse laser to be detected by using the discharge segment laser power analysis expression P' =g (R, C, V and t), wherein the calculated time point value is t _w+(2t_s/m)*j_right, the voltage signal amplitude is V _n+1.

3. The pulsed laser power measurement method based on an integrating circuit of claim 2, wherein:

in step 1, the photodetector is a single photodetector or a photodetector array.

4. The pulsed laser power measurement method based on an integrating circuit of claim 3, wherein:

When the photodetectors are photodetector arrays, each photodetector samples the digital voltage signal output by the RC integrating circuit at the same sampling interval t _s in a time sequence.

5. The method for measuring pulse laser power based on an integrating circuit according to claim 4, wherein:

when the photoelectric detector array includes N photoelectric detectors, N is an integer greater than or equal to 2, and step 5 specifically includes:

5.1, sequentially calculating an absolute value epsilon _j (k) = |P (j, k) -P' (j, k) | of a difference between laser power values corresponding to m+1 time point values of a charging section and a discharging section of the kth photoelectric detector to obtain a j _right (k) sequence value corresponding to a minimum value of epsilon _j (k), wherein k=1, 2,3, … and N;

5.2 calculating the average value of the j _right (k) sequence values J _right is the minimum value of ε _j.

6. The pulsed laser power measurement method based on an integrating circuit according to any one of claims 1-5, wherein:

In step 5, when the minimum value of epsilon _j is larger than the measurement precision given by the measurement device, selecting a value larger than the initial value of m to re-divide the time area, and repeating steps 3 to 5 until the minimum value of epsilon _j meets the measurement precision.

7. The method for measuring pulse laser power based on an integrating circuit according to claim 6, wherein:

in step 3, the initial value of m is 100.