Study Of Thz Radiation Of D₂O Molecules Pumped By TEA CO₂ Laser

Terahertz wave has many unique properties. THz technology has great potential of application in medicine,national defense,information communication,industrial application and imaging. The lack of efficient THz radiation sources has restricted the development of the THz technology. To achieve good beam quality, output energy, stable laser output, small size laser radiation is one of emphasis in the THz study area. Optically pumped THz laser is still an very efficient THz radiation sources at present with good beam quality, high output power and the potential advantages of continuous tuning,as the technology becomes more mature,pratical and highly reliable. THz radiation generated by Optically-Pumped D2O gas molecules is mainly studied in this paper.Theoretically,firstly, the theory which based on the semi-classical density matrix equationsthe has been introduced . The gain coefficients of infrared pumping signal and THz wave laser signal were deduced by solving the density matrix equation of three-level molecular system .Secondly,the theoretical simulation model of the transmittance of output coupling mirror in the optically pumped THz laser has been established and calculated. The influence of the physical parameters of metal mesh including substrate thickness, width, period constants to the transmittance has been discussed and the related tuning curves of transmittance has been received.which will be helpfull for the further study of the THz laser.Experimentally,the relationship between the intensity of the output THz laser and the laser parameters ,such as the working gas pressure and the intensity of pumping laser ,has been studied when TEA CO₂ laser working under the multi transverse mode and the fundamental transverse mode accordingly.the factors influencing the efficiency of THz laser have been discussed.the optimum operation pressure has been obtained and photo conversion efficiencies have been achieved. The laser-induced pump absorption saturation has been discussed at low gas pressure. The wavelength of THz laser has been measured by F-P interferometer .the output THz laser signal was 385μm in wavelength,50 ns in pulse wilth. The energy distribution curve of THz laser beam has beem measured. The pulse waveform of THz laser and pump laser and the size of the distribution of pumped laser have been measured when TEA CO₂ laser working under the multi transverse mode and the fundamental transverse mode accordingly.