Generation Of Terahertz Radiation Based On Optical Methods

The technological of terahertz radiation source plays an important role interahertz (THz) technique. Presently, the main methods of obtaining the terahertzradiation mainly include electronics and photonics methods, and the nonlinear opticaleffect has attracted great interest for its advantages of high peak power, widelytunable range, operating at room temperature, compactness and low cost. It ismainly divided into three categories, such as nonlinear optical difference frequencygeneration (DFG), four-wave mixing generation (FWM) and terahertz parametricoscillator generation based on Raman effect.The main content and innovation of this paper are summarized as follows:1. The transmission equation of picosecond optical pulses in optical fiber andfour-wave mixing (FWM) theory have been derived from the Maxwell equations. Thedispersion and loss characteristics of the octagonal photonic crystal (O-PCF) fiberwere obtained. When the incident wavelength=1.55m, the chromatic dispersionwas in the range of±0.5ps/(km·nm), the confinement loss was only0.06dB/km andthe nonlinear coefficient was86.5W/km. The condition of collinear phase matchingwas analyzed, and it is shown that when the wavelength ranged of1.48~1.62m, thefrequency range of the generated THz waves was7.07~7.74THz. Finally, wesimulated the FWM process in O-PCF. When the peak power pulse width andrepetition frequency of the pump and signal were2kW12ps and60MHz respectively,the THz at7.42THz with maximal peak power of2.55W and the peak conversionefficiency of0.89‰was obtained. The time-domain pulse diagram has also beenobtained.2. Both collinear and noncollinear phase matching conditions of differencefrequency generation (DFG) THz radiation in GaP crystal have been theoreticallysimulated based on three-wave mixing (TWM) theory. The pump wavelength is1.064m and the signal wavelength is tuning from1.065to1.086m. When thenoncollinear phase matching condition is satisfied and the noncollinear angleinextchanges from1.7to70.8, the corresponding THz waves ranged from0.26THz to5.27THz are obtained. The relationship of noncollinear angleinextand angleTHzextofTHz radiation outside the crystal is obtained. When the noncollinear phase matching condition is satisfied, frequency range of the generated THz is0.26~5.27THz and thephase mismatch range is0.36~28.79cm-1.3. The experimental system of collinear DFG in GaP crystal has been set up.Above all, the signal wave ranged of1.069~1.074m is generated byMgO:LiNbO3-OPO. In succession, collinear DFG progress has been interactingbetween pump (1.064m) and signal waves (1.071m) in GaP crystal with dimensionof10×10×5mm~3. Finally, the maximal peak power of the generated THz is29.1W.