The maximum output performance of the traditional high power laser facility[
High Power Laser Science and Engineering, Volume. 1, Issue 3-4, 3-43-4000126(2013)
Energy measurement system of a large-aperture high power laser experiment platform
An energy measurement system in a Large-aperture high power laser experiment platform is introduced. The entire measurement system includes five calorimeters, which carry out the energy measurement of the fundamental frequency before the frequency conversion unit, remaining fundamental frequency, remain second-harmonics, third harmonics, as well as the energy balance measurement after the frequency conversion unit. Combinational indirect calibration and direct calibration are employed to calibrate the sampling coefficients of the calorimeters. The analysis of the data showed that, regarding the energy balance coefficients, combinational calibration approach gives a higher precision, and leads to an energy balance with 1%; and regarding the energy sampling coefficients for the various wavelengths after the frequency conversion, the results from direct and combinational calibration are consistent. The uncertainties for all energy sampling coefficients are within 3%, which guarantees the reliability of the energy measurement for the laser facility.
1. Introduction
The maximum output performance of the traditional high power laser facility[
Sign up for High Power Laser Science and Engineering TOC Get the latest issue of High Power Laser Science and Engineering delivered right to you!Sign up now
This article introduces an energy measurement system for Large-aperture High Power Laser
Experiment Platform[
2. System optical paths
Our Large-aperture High Power Laser Experiment Platform is a comprehensive experiment
verification platform that can output more than tens of thousands of joules. It can be
used for comprehensively evaluating the load capacity of the optical equipment,
component and system under high energy flux level. The optical paths of its energy
measurement system are listed as in figure
There are two reflection mirrors in the third-harmonics system to turn the optical path. After being transmitted from the second reflection mirror, and being collimated by the three-wavelength collimation lens, it enters the three-wavelength calorimeter. That accomplishes the sampling of all three wavelengths.
The light through the third-harmonics beam shrink system is a mixture of fundamental frequency, second-harmonics and third-harmonics. After being reflected by dichroic mirror 1 and dichroic mirror 2, the light enters third-harmonics calorimeter. The purpose of dichroic mirror 1 is to only transmit third-harmonics light, and only reflect fundamental frequency and second-harmonics light; dichroic mirror 2 is a half-transmission-half-reflection mirror. At the same time, it serves as a wave aberration compensation for any measurement that follows.
After the mixed light is reflected by dichroic mirror 1, it becomes a mixture of fundamental frequency and second-harmonics. Due to the chromatic aberration, it needs to be collimated. After being converged by the energy convergence lens, the light was projected on dichroic mirror 3. Its reflected light enters the fundamental frequency calorimeter, and the transmitted light enters the second-harmonics calorimeter.
A filter was placed in front of each single-wavelength calorimeter, to ensure that the light entering the calorimeter is actually of a single wavelength.
Based on the modularization design requirement, all the calorimeters in the system use
uniform calibers, and are composed of energy sensors, amplifiers, and display modules.
The entire energy measurement system is centrally sampled and processed through remote
control[
3. System calibration
For the fundamental frequency part of the main optical path, the energy values of two
key points need to be known: the main amplifier output energy
Here are four calorimeters after the frequency conversion unit. They are used to measure
the energy of the remaining fundamental frequency, remaining second-harmonics,
third-harmonics, and to sample the total energy for the purpose of energy balance. Their
relationship can be shown in figure
3.1. Direct calibration
We place the 420 standard calorimeter after the third-harmonics sampling
mirror 1, and insert an absorbing glass element between the frequency
conversion unit and the mirror 1, (two
Then, based on the energy transmission-reflection rate of different wavelengths from
the online calibration of the third-harmonics sampling mirror 1, we get
the single-wavelength sampling coefficients,
3.2. Combinational calibration
In the direct calibration approach, often we have a small number of calibrated laser
shot missions. Also because the inserted absorbing glass element is difficult to
guarantee a single-wavelength output, it results in a fair amount of dispersion in
the sampling coefficient. Therefore we can also employ combinational calibration
approach. There is no need to insert additional filters. The steps to calibrate the
sampling coefficients are as follows: first, we place the 420 calorimeter after the
third-harmonics sampling mirror 1. Within the range of
4. Results and analysis
Table
We can see from figure
|
There are two areas of reasons for this situation. First there is a sensitivity
difference in the calorimeters themselves. Since under the normal phase matching
condition, the second-harmonics light from the harmonics crystal are almost all
converted into third-harmonics with the crystal, the remaining second-harmonics light is
far less than the remaining fundamental frequency and third-harmonics light. The design
of the diagnosis system takes many factors into consideration, so that the energy
sampling coefficients have a relatively smaller difference before entering the
photosensitive surface in the calorimeter. Therefore, in order to guarantee the
measurement precision of the second-harmonics energy, the sensitivity to the
second-harmonics is about 10 times of that in the remaining fundamental frequency,
third-harmonics, three-wavelength calorimeters, all of which have similar sensitivities.
So during direct calibration, taking the measurement range of the 420 calorimeter into
consideration, the actual energy value that enters the second-harmonics calorimeter is
at the center of the linear region of this calorimeter[
Based on the analysis above, the error from combinational calibration approach is smaller. The obtained energy balance relationship is with 1%. We can use it as the guidance on the accuracy of the energy measurement. Once the deviation exceeds this value, the reason is either the measured energy values are not within the linear regions of the calorimeters, or there is a change in the energy balancing relationship. For the latter, we need to check the optical component damage in optical path.
In the process of energy balancing coefficient calibration, only the readings from four
calorimeters need to be recorded. There is no need to record the input energy levels. In
order to obtain the input energy level, we need to calibrate the energy sampling
coefficients of the optical path. Due to the limited number of laser shot missions, we
only apply one group of calibration data, that from the direct calibration, in both
groups of results. The result can be seen in table
|
In order to verify the accuracy of the calibration data, we accumulate the laser shot
results that follow. More specifically, we use the main amplifier energy to backward
calculate the total energy after the crystal,
The experiment results can be seen in figure
We can see from figure
To explain such dispersions, besides the size of our data, also lies within the fact
that the derived energy from main amplifier
Regarding the system error, the main reason lies in that the fundamental frequency transmission rate in the frequency conversion unit is 88%, (no frequency conversion), in place of the total transmission rate of the frequency conversion unit. When there is significant harmonics conversion efficiency, the total transmission rate increases. That is also the reason why the third-harmonics sampling coefficients derived from the main amplifier is relatively smaller.
5. Conclusions
This article introduces the energy measurement system in a Large-aperture high power laser experiment platform, and its calibration process. The data analysis shows that, regarding the energy balancing coefficients, results obtained from the combinational approach has a higher precision. The energy balance can be controlled within 1%. It can accurately monitor the reliability of the energy sampling efficiency. Regarding the energy sampling coefficients to all the wavelengths after the frequency conversion, the results from direct and the combinational calibration approaches are consistent. But due to the limited number of laser shot missions, there is about 2% system error in the total output energy, along with 2% dispersion. However, the results are guaranteed to ensure the single wavelength energy measurement controlled within the 4.7% uncertainty range. To further improve the energy measurement accuracy of the third-harmonics, it is necessary to have a large number of laser shot statistics. This will be the focus of our future work.
[1] S. C. Burkhart, W. C. Behrendt, I. Smith. and UCRL-LR-105821-95-1..
[2] X. M. Zhang, W. G. Zheng, X. F. Wei. Proc SPIE, 562, 7(2005).
[4] Z. Q. Lin. Chinese J. Lasers, 37, 9(2010).
[6] P. Martin, A. Morono, E. R. Hodgson. J. Nucl. Mater., 329(2004).
[7] A. Conde, T. Alger, S. Azevedo, J. Chang, S. Glenn, L. Kegelmeyer, J. Liebman, P. Whitman. and UCRL-PROC-236458 (2007)..
[8] Paul J. Wegner, Bruno M. Van Wonterghem. and UCRL-JC-123070..
[9] C. E. Thompson, D. E. Decker, C. F. Knopp. and UCRL-JC-130034 (1998)..
[10] Z. T. Peng, X. F. Wei, H. Y. Yuan, X. J. Fu, D. H. Chen, Z. H. Sun, H. Liu, L. B. Xu. Infrared Laser Eng., 40, 1111(2011).
[12] M. Xia, X. Shan, J. Q. Gao, W. Sun. Acta Meteorol. Sin., 30, 6A, 112(2009).
[13] T. Xu, J. Yu, Q. M. Fan, Y. Q. Deng. Acta Meteorol. Sin., 30, 6A, 116(2009).
[14] J. F. Wei, K. Zhang, S. S. Qian, X. Y. Gao, S. Zhou, D. H. Zhou. High Power Laser and Part. Beams, 19,7, 1103(2007).
[15] J. Yu, L. M. Xiong, X. Tao, Q. M. Fan, Y. Q. Deng, Y. P. Zhang. Acta Meteorol. Sin., 30, 6A, 80(2009).
Get Citation
Copy Citation Text
Yanwen Xia, Yue Liang, Sen Li, Junpu Zhao, Zhitao Peng, Hongguang Li, Hua Liu, Zhihong Sun, Kuixing Zheng, Xiaofeng Wei. Energy measurement system of a large-aperture high power laser experiment platform[J]. High Power Laser Science and Engineering, 2013, 1(3-4): 3-43-4000126
Category: Research Articles
Received: Nov. 6, 2013
Accepted: Nov. 30, 2013
Published Online: Nov. 19, 2018
The Author Email: Yanwen Xia (xiayanwen1972@163.com)