Research On Optically Pumped CH₂F₂ Gas Molecules Terahertz Laser And Stability Control

Terahertz wave is between infrared wave and microwave of the electromagnetic spectrum. It is with some special virtues like good penetrability and low ionization energy, which endows it with great scientific value and broad application foreground in many fields. Optically- pumped gas laser devices have a relatively high level of power and high pump efficiency. But it takes several troubles to practical applications for the great fluctuation of the power of free running leading to the consequence that it cannot work steadily for a long time. The stability control of pump laser mainly means tuning the cavity length. In this paper, pulsed Terahertz laser can be obtained by pumping the CH₂F₂ molecule with a CO₂ laser. Besides, an electronic stability control system based on FPGA will be introduced which can adjust the grating angle of CO₂ laser as well as conduct the stability control of frequency so as to enhence the long-term average power and duration siginificantly.The operational principle of optically-pumped CH₂F₂ molecule is analyzed from the theoretical perspective. Furthermore, we discuss the effect on laser frequency caused by the variation of cavity length and grating incidence angle. A new frequency stability control method, namely, automatic compensation of grating angle adjustment, is proposed and corresponding scheme towards pump laser is also designed.In the aspect of experiment, the semi external cavity pump laser of optically-pumped gas laser system is improved such that slight change of grating angle can be achieved through the expansion of piezoelectric ceramics. We obtain a Terahertz pulsed laser output at a repeat frequency rate of 2.5 kilohertz with the highest average power of 11 mW when we use impulse signal generator to trigger the current switch so as to obtain the pulsed laser served as pimping source. Then we design a stability control system based on FPGA, which can adjust the CO₂ laser in real time according to the extreme value method, it can make the pump frequency near the absorption peak of THZ gains medium. Ultimately, the THZ power is stabilized at about 9mW for nearly 10 minutes, whose power stability increases by one order of magnitude compared with free running.