# Working principle of laser energy meter standard device

by：Caodahai     2021-09-26
The laser energy standard device measured by the beam splitting method is mainly composed of three parts: a laser radiation source, a beam splitter and a standard energy meter.　　 The working principle of the standard device is shown in Figure 1. The beam emitted by the laser source passes through the wedge beam splitter and becomes three beams. Two standard laser energy meters 1 and 2 measure the pulse energy of the sub-1 beam and the main beam at the same time, and the energy ratio of the two beams can be obtained. In the same way, the energy ratio of the sub-2 beam to the main beam is obtained. When the light source and the wedge beam splitter are not moving, the beam splitting ratio of the 3 beams of light energy is constant. As long as you know the energy of one of the light beams, you can use the beam splitting ratio to get the energy of the other two light beams. Then use the standard energy meter and the measured energy meter to detect the energy of the two beams at the same time. According to the energy value and the split ratio detected by the standard device, the standard value of the measured energy meter can be obtained, and the standard value and the measured value of the measured energy meter can be obtained. Compare to get the correction factor of the measured energy meter. Measurement experiment 　　 During the measurement process, it is necessary to make sure that the laser beam is perpendicular to the receiving surface of the detector, and it is all received by the detector.　　 The splitting ratios of the main beam to the sub 1 beam and the sub 2 beam measured by the experiment are 22.926 and 24.622 respectively, which are in good agreement with the theoretical calculations of 23.050 and 24.986. The slight difference may be caused by light scattering and incident angle. According to the experimentally measured splitting ratio of the main beam to the sub-1 beam and the sub-2 beam, we can also obtain the sub-1 beam to the sub-2 beam splitting ratio 1.074.　　 Place the standard energy meter on the optical path of the main beam, and place the laser energy meter under test on the sub 1 (or sub 2) optical path. The measurement results are shown in Table 3.　　 It can be seen from Table 3 that the correction factor of the tested laser energy meter in automatic transmission is 1.00, and the relative standard deviation is 0.3%. The correction factor obtained by the experimental measurement is completely consistent with the correction factor given by the Chinese Academy of Metrology for the instrument certificate. It can also be seen from Table 3 that the repeatability of the energy measurement of the standard energy meter and the measured energy meter itself is not very good, which is largely caused by the instability of the light source, and sometimes even double pulse output occurs. The measurement method cleverly avoids the error caused by this reason, thereby reducing the uncertainty.　　3. Uncertainty analysis 　　In this standard device, the measurement uncertainty of the system is composed of the stability of the supporting light source, the repeatability of the beam splitting ratio of the beam splitter, and the standard uncertainty introduced by the standard laser energy meter. In the calibration measurement of a certain measured energy meter, the composite uncertainty should also include the uncertainty of the repeated measurement of the standard laser energy meter and the uncertainty of the repeated measurement of the measured energy meter. According to the basic theory, the first three items should belong to type B measurement uncertainty, and the last two items belong to type A measurement uncertainty. It should be pointed out that the repeatability of the splitting ratio of the beam splitter is used in the calibration measurement according to the known inherent properties of the standard device, but it is obtained through the statistical results of repeated measurements. 1. Standard uncertainty introduced by the stability of the standard supporting laser source The modified laser energy meter standard device adopts the method of beam splitting measurement, so that the standard energy meter and the measured energy meter receive the same pulse from the light source at the same time, eliminating the light source The influence of instability on the measurement, therefore, the stability uncertainty ub1 of the standard supporting laser source can be ignored. 2. The standard uncertainty introduced by the repeatability of the splitting ratio of the beam splitter The measurement repeatability of the splitting ratio of the beam splitter is one of the important factors affecting the measurement uncertainty of the system, which has been determined in the previous section 2 related experiments , The measurement repeatability of the beam splitting ratio of this system is 0.25%, that is, ub2u003d0.25% (1) 　　 3. Standard uncertainty introduced by the standard laser energy meter The verification given by the Chinese Academy of Metrology on the standard device used in this device The certificate states that the extended uncertainty of the standard energy meter is Uu003d3% (ku003d2), and its standard uncertainty is ub3u003d1.5% (2) 　　 4. Measurement uncertainty of repeated calibration Measurement of repeated calibration The uncertainty includes the uncertainty of the repeated measurement of the standard laser energy meter and the uncertainty of the repeated measurement of the measured energy meter. If these two items are calculated separately and then combined, the instability of the light source will be included. Since the use of the beam splitting method has eliminated the influence of the instability of the light source, errors will occur in the separate calculations. In this case, it is only possible to perform statistical analysis on the correction factor given by the final calibration, so as to obtain the uncertainty of the repeated calibration. According to the measurement experiment of the correction factor in the previous section 2, the uncertainty of repeated measurement of the standard laser energy meter can be obtained as 0.3%, that is, uau003d0.3% (3) (The above is edited and compiled from the network by the fiber laser cutting machine. For details, see www. .gnlaser.com)
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