Device and method for measuring thermal load caused by excited state absorption in laser gain crystal

A method for measuring a thermal load caused by ESA in a laser gain crystal, wherein the method is performed with the following device, which comprises:

• a single-frequency laser (1), a power meter (2), a spectroscope (3), an F-P cavity (4), a photodetector (5), an oscilloscope (6), a signal generator (7), and a high-voltage amplifier (8),
• wherein the spectroscope (3), the F-P cavity (4), the photodetector (5), the oscilloscope (6), the signal generator (7), and the high-voltage amplifier (8) are connected in sequence,
• wherein an output laser of the single-frequency laser (1) passes through the spectroscope (3) and is injected into the power meter (2), a part of the laser passing through the spectroscope (3) is injected into the F-P cavity (4) and converted into an electrical signal by the photodetector (5), and the electrical signal output by the photodetector (5) is input to the oscilloscope (6),
• wherein the oscilloscope (6) is configured to display single-frequency characteristics of the single-frequency laser (1) under different incident pump powers,
• wherein the oscilloscope (6) is connected to the signal generator (7), and the signal generator (7) is configured to generate a low-frequency scan signal, and
• wherein the low-frequency scan signal is amplified by the high-voltage amplifier (8) and loaded to a piezoelectric ceramic attached to the F-P cavity (4),
• and the method comprises:
• obtaining a threshold when a pump power is decreased and optimal operating point power of the single-frequency laser;
• obtaining cavity parameters of the single-frequency laser;
• obtaining thermal focal lengths on tangential and sagittal planes of the laser gain crystal inside the single-frequency laser according to formulas for the thermal focal lengths on the tangential and sagittal planes;
• obtaining individual ABCD matrices of the laser gain crystal on the tangential plane and the sagittal plane based on the thermal focal length on the tangential plane, the thermal focal length on the sagittal plane, and the cavity parameters of the single-frequency laser;
• substituting the threshold when the pump power is decreased and the cavity parameters of the single-frequency laser into ABCD transfer matrices on the tangential plane, the ABCD transfer matrices on the sagittal plane, and a condition of stability ranges, to obtain the thermal load corresponding to the threshold when the pump power is decreased;
• obtaining the ESA thermal load based on the thermal load corresponding to the threshold when the pump power is decreased;
• and
• substituting the optimal operating point power and the cavity parameters of the single-frequency laser into the ABCD transfer matrices on the tangential plane, the ABCD transfer matrices on the sagittal plane, and the condition that laser beam size at the laser gain crystal on the tangential plane is the same as that on the sagittal plane, to obtain an ESA thermal load at the optimal operating point.