A method for measuring the chirp rate of a chirped volume grating

Abstract

The application discloses a chirp rate measurement method of a chirped volume grating, and comprises the following steps: constructing a measurement light path; starting a laser and an energy detector; adjusting the included angle and relative position of a to-be-measured chirped volume grating sample and a laser output light beam by adjusting an angle adjusting table and a translation table, recording the angle and position when the chirped volume grating diffracts, and calculating an angle average value; and calculating the chirp rate of the to-be-measured chirped volume grating sample according to a formula. The measurement principle is simple, the calculation method is clear, and the chirp rate of a chirped volume grating of any specification can be measured.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of measurement of chirped volume Bragg grating, and particularly to a method for measuring chirp rate of chirped volume Bragg grating. BACKGROUND

[0002] Chirped pulse amplification (CPA) is the core technology of the current high-power laser system. In 1985, the concept of chirped pulse amplification (CPA) was introduced into the field of laser, which laid the theoretical foundation for further improving the peak power of laser pulse.

[0003] In 1996, in order to make the CPA system compact, stable, reliable and cost-effective, Almantas Galvanauskas et al. of IMRA Company in the United States proposed a scheme of using chirped volume Bragg grating (CVBG) as a pulse stretcher or compressor in the system. By using the phase reciprocity of CVBG structure, i.e. it can provide the same value of dispersion with opposite polarity in the forward and reverse directions, only need to make the laser pulse incident to the CVBG from the opposite direction, the pulse can be stretched and compressed at the same time. It can be seen that using CVBG as stretcher or compressor can not only solve the problem of dispersion mismatch, but also greatly reduce the space of CPA system, and avoid the complex assembly of optical elements and optical path alignment.

[0004] Chirped volume Bragg grating is an optical diffraction element with linearly changing grating period along its thickness direction, and the speed of the period change is called chirp rate. After the preparation and before the use of chirped volume Bragg grating, its chirp rate needs to be measured. At present, researchers measure the diffraction efficiency curve of chirped volume Bragg grating to indirectly calculate the chirp rate of chirped volume Bragg grating, but this method is tedious and long. Because in order to make the fitting curve highly coincide with the measured curve, the method requires multiple curve fitting to make the fitting curve infinitely approximate to the measured curve.

[0005] In view of the above problems, it is necessary to propose a method for measuring the chirp rate of chirped volume Bragg grating, which can meet the measurement requirements of chirp rate of chirped volume Bragg grating of any specification and type. SUMMARY

[0006] The purpose of the present application is to measure the chirp rate of chirped volume Bragg grating of any specification, and to achieve this purpose, the technical solution of the present application is as follows:

[0007] A method for measuring the chirp rate of chirped volume Bragg grating, characterized in that it comprises the following steps:

[0008] S1: Constructing a measurement light path: along the optical axis direction of the laser, the to-be-measured chirped volume grating sample and the energy detector are placed in sequence along the optical axis, the to-be-measured chirped volume grating sample is fixedly placed on a translation stage, and the translation stage is fixed on an angle adjusting stage;

[0009] S2: Turn on the laser, so that the laser output beam is incident on the to-be-measured chirped volume grating sample; turn on the energy detector, and monitor and record the corresponding data in real time according to the energy change of the light beam after passing through the to-be-measured chirped volume grating sample;

[0010] S3: The position parameter of the output beam of the laser incident on the to-be-measured chirped volume grating sample is recorded as z1, the to-be-measured chirped volume grating sample is rotated through the angle adjusting stage, when the energy detector collects the transmitted light beam energy, the angle adjusting stage has been turned through the angle size θ1 is recorded; the angle adjusting stage is reset, and the θ1 is repeatedly measured multiple times, and the average value is recorded and calculated

[0011] S4: The angle adjusting stage is reset, the output beam of the laser is adjusted to be incident on the to-be-measured chirped volume grating sample through the translation stage, and the position parameter is recorded as z2; the step S3 is repeated, the angle size θ2 of the angle adjusting stage turned through is recorded by repeatedly measuring multiple times, and the average value is calculated

[0012] S5: The chirp rate C of the to-be-measured chirped volume grating sample is calculated, and the formula is as follows:

[0013]

[0014] In the formula, λ is the wavelength of the laser, n is the refractive index of the to-be-measured chirped volume grating sample, is the grating vector tilt angle of the to-be-measured chirped volume grating sample. The calculated value is taken as the chirp rate of the to-be-measured chirped volume grating sample 4.

[0015] Of course, for multiple groups of different position parameters z1, z2, the steps S3-S4 are repeatedly measured multiple times, and the corresponding According to the step S5, multiple groups of z1, z2, The chirp rate C of the corresponding to-be-measured chirped volume grating sample is calculated, and the average value is calculated At this time, the average value can be taken as the chirp rate of the to-be-measured chirped volume grating sample 4.

[0016] The working medium of the laser can be but is not limited to gas and solid, and the working wavelength can be but is not limited to the range of 300 nm to 1100 nm, and other performance parameters of the laser such as wavelength accuracy and line width need to be determined according to the test requirements of the chirped volume grating.

[0017] The chirped volume grating is any specification and type of chirped volume grating, including but not limited to a transmission type volume grating, a reflection type volume grating, a face incidence type volume grating, a stripe tilt chirped volume grating and the like.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] 1. The chirped volume grating of any specification and type can be measured.

[0020] 2. The chirped volume grating is regarded as a whole composed of a plurality of period constant but different volume gratings, the average value of the angle at which the transmission beam energy is suddenly reduced can be obtained by measuring a plurality of different positions, and the average value of the corresponding chirp rate can be calculated. The measurement precision of the chirp rate of the chirped volume grating is improved in the manner of the average value of the corresponding chirp rate.

[0021] 3. The diffraction efficiency curve of the chirped volume grating does not need to be measured, and the chirp rate of the chirped volume grating is indirectly calculated by the manner of the fitting curve being highly coincided with the measured diffraction efficiency curve of the chirped volume grating in the prior art. The chirp rate of the chirped volume grating is obtained only by collecting the position parameters and the angle at which the transmission beam energy is suddenly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The flow chart of the chirp rate measurement method of the chirped volume grating in the present application.

[0023] Figure 2 The chirp rate measurement optical path diagram of the chirped volume grating constructed in the present application.

[0024] Figure 3 The position parameters and the angle data of the angle adjustment table 2 turned in the plurality of measurements in the embodiment.

[0025] In the figure, 1 is a laser, 2 is an angle adjustment table, 3 is a translation table, 4 is a sample of the chirped volume grating to be measured, 5 is an energy detector, the solid line is a theoretical curve, the discrete points are experimental data, and the dashed line is a fitting curve of the experimental data. DETAILED DESCRIPTION

[0026] The present application will be further described in detail below in combination with the drawings and embodiments, but the protection scope of the present application should not be limited thereto.

[0027] Embodiment: A sample 4 of the chirped volume grating to be measured with the length, width and height of 16 mm, 4 mm and 5 mm respectively is measured, the refractive index n of the sample is 1.5121, the grating vector tilt angle is 0.5°, and the grating vector is 0.5°. The designed chirp rate C is 0.435 nm / cm. The measurement steps in the embodiment of the present application are as follows:

[0028] The measured chirped volume grating sample 4 is regarded as a transmission volume grating according to the transmission-reflection performance of the volume grating at different incident surfaces (the performance only depends on the apparent size of the volume grating, the relative relationship between the grating vector of the volume grating and the spatial properties of the probe light, and the volume grating can be divided into transmission, reflection and adjacent incidence volume gratings according to the relative relationship), so as to evaluate the chirp rate of the measured chirped volume grating sample 4 by using the chirp rate calculation formula of the measured chirped volume grating sample on the basis of the experimental test results.

[0029] (A) Construct a measurement light path, as shown in the figure, place the laser 1, the angle adjusting table 2, the translation table 3, the measured chirped volume grating sample 4 and the energy detector 5 along the optical axis in turn, wherein the angle adjusting table, the translation table and the measured chirped volume grating sample are stacked from bottom to top and fixed; the measurement beam is output from the laser 1, is incident to the measured chirped volume grating sample 4 fixed on the mechanical device composed of the angle adjusting table 2 and the translation table 3 from bottom to top, and the outgoing beam is received by the energy detector 5; Figure 2

[0030] (B) Turn on the laser 1, adjust the wavelength of the output beam of the laser to 413.1 nm, and make the output beam incident to one end of the measured chirped volume grating sample 4, and the position parameter is recorded as z1=5 mm. Turn on the energy detector 5, and monitor and record the corresponding data in real time for the change of the beam energy after passing through the measured chirped volume grating sample 4;

[0031] (C) Rotate the measured chirped volume grating sample 4 through the angle adjusting table 2, when the energy detector 5 collects the transmission beam energy, record the angle θ1 that the angle adjusting table 2 has turned; repeat the measurement for multiple times to obtain θ1=36.7071°, 36.7245°, 36.7242°, 36.7052°, 36.7116°, 36.6952°, 36.6895°; calculate the average value

[0032] (D) Reset the angle adjusting table, adjust the position of the output beam of the laser incident to the measured chirped volume grating sample 4 through the translation table 3, and the position parameter is recorded as z2=11 mm; when the angle adjusting table 2 rotates the measured chirped volume grating sample 4 to the energy detector 5 collects the transmission beam energy, record the angle θ2 that the angle adjusting table 2 has turned; repeat the measurement for multiple times to obtain θ2=36.6973°, 36.6584°, 36.6656°, 36.6709°, 36.6975°, 36.6586°, 36.6831°; calculate the average value

[0033] ​(E) The chirp rate C of the chirped volume grating sample 4 to be measured is obtained by combining the following formula, which is basically the same as the design value: C = 0.4355 nm / cm.

[0034]

[0035] Of course, further, in order to improve the accuracy of the calculation result, the output light beam of the laser can be adjusted to be incident to the chirped volume grating sample to be measured by the translation stage, and a plurality of different position parameters z1, z2 are obtained; the steps S3-S4 are repeated multiple times to obtain the corresponding According to the step S5, a plurality of z1, z2, The chirp rate C of the corresponding chirped volume grating sample to be measured is calculated, and the average value At this time, the average value is taken as the chirp rate of the chirped volume grating sample to be measured.

[0036] The above examples are used to explain the present application, but not to limit the present application, and any modification and change made to the present application within the spirit and protection scope of the claims of the present application, falls into the protection scope of the present application.

[0037] Experiments show that the present application meets the measurement requirements of the chirp rate of any specification and type of chirped volume grating, the optical path of the measurement device is simple and easy to build, and the adjustment is flexible, and the calculation process involved is simple and clear.

Claims

1. A method for measuring a chirp rate of a chirped volume grating, characterized in that, It comprises the following steps: S1: constructing a measuring light path: placing a to-be-measured chirped volume grating sample (4) and an energy detector (5) in sequence along the optical axis of a laser (1) and in the same optical axis direction, the to-be-measured chirped volume grating sample (4) being fixedly placed on a translation stage (3), and the translation stage (3) being fixed on an angle adjustment stage (2); S2: starting the laser (1) to make the laser output beam incident on the to-be-measured chirped volume grating sample (4); starting the energy detector (5) to monitor and record corresponding data in real time for the change in the energy of the light beam after passing through the to-be-measured chirped volume grating sample (4); S3: the output beam of the laser (1) is incident to the position parameter z1 of the to-be-tested chirped volume grating sample (4), the to-be-tested chirped volume grating sample (4) is rotated through the angle adjusting table (2), when the energy of the transmitted beam collected by the energy detector (5) suddenly decreases, the angle θ1 through which the angle adjusting table (2) has been turned at this time is recorded; the angle adjusting table (2) is reset, and the measurement of θ1 is repeated multiple times, and the average value is recorded and calculated S4: reset the angle adjustment stage (2), adjust the output beam of the laser (1) to the position of the to-be-measured chirped volume grating sample (4) through the translation stage (3), and the position parameter is recorded as z2; repeat step S3, record the angle size θ2 of the angle adjustment stage (2) that has been turned through multiple repeated measurements, and calculate the average value S5: calculating the chirp rate C of the to-be-measured chirped volume grating sample (4), the formula being as follows: In the formula, λ is the wavelength of the laser (1), n is the refractive index of the to-be-tested chirped volume grating sample (4), The calculated value is the grating vector tilt angle of the to-be-tested chirped volume grating sample (4), and the calculated value is taken as the chirp rate of the to-be-tested chirped volume grating sample (4).

2. The method for measuring the chirp rate of a chirped volume grating according to claim 1, characterized in that, The working medium of the laser comprises a gas or a solid, and the working wavelength is in the range of 300 nm to 1100 nm.

3. The method of claim 1, wherein the chirp rate of the chirped volume grating is measured by the method. The chirped volume grating is any specification and type of chirped volume grating, including a transmission type volume grating, a reflection type volume grating, an adjacent surface incidence type volume grating, and a stripe tilt chirped volume grating.

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