Broadband terahertz pulse generation by optical rectification in GaP crystals

Abstract

We demonstrate a broadband (0.3–7 THz) terahertz pulse generation using GaP generation and detection crystals with an 80-MHz-repetition-rate Ti:Sapphire laser. We also use simulations of cascaded terahertz generation to model the observed terahertz gain profiles. The efficient generation of the broadband terahertz pulses is based on optimizing the phase matching between the optical and terahertz pulses, which is achieved by tuning the wavelength of the laser. We observed further improvement in the generation efficiency due to a mismatching of the imaginary part of the complex wavevectors. Together, these effects allow the use of thicker crystals and thus lead to increased terahertz emission. Our results show that optical rectification by GaP can be used to generate broadband terahertz pulses with MHz-repetition-rate lasers up to a dynamic range that is comparable to commonly used sources like ZnTe and photo-conductive antennas.

Towards Intense THz Spectroscopy on Water: Characterization of Optical Rectification by GaP, OH1, and DSTMS at OPA Wavelengths

“…(c) Normalized spectrum of the THz field as a function of λ P . As expected, the frequency range is increased for shorter wavelengths [84], it is broad at λ P = 1200 nm and narrow at λ P = 2500 nm. (d) Estimated conversion efficiency of NIR radiation into THz radiation as a function of pump color.…”

“…Previously, we investigated the THz emission by GaP pumped by a mode-locked oscillator tunable between 700 and 1000 nm [84]. We found that the THz emission covers a broad range at λ P = 900 nm, and that the frequency range of the emitted spectrum decreases for longer pump wavelengths.…”

“…OR typically allows us to generate intense THz radiation below 5 THz (sketched in light green and light red in Figure 1c), while DFG covers higher frequencies (dark green and dark red in Figure 1c). Both inorganic (LiNbO 3 [66][67][68][69][70][71][72][73][74][75][76][77], GaSe [78][79][80], ZnTe [81,82], LiGaS 2 [83], GaP [84][85][86][87][88][89]) as well as organic (DSTMS [89][90][91][92], OH1 [93][94][95][96][97], DAST [98,99], DPFO [100], HMQ-TMS [101], OHQ-N2S [102]) crystals are phase-matched in the NIR and can emit pulsed THz fields with peak amplitudes in excess of 1 MV/cm. The approximate spectrum of the strongest THz pulses generated to date by non-linear optical methods in inorganic [62,64] and organic [63,65] crystals are shown in green and in red in Figure 1c, respectively.…”

Optical rectification of ultrafast Yb lasers: pushing power and bandwidth of terahertz generation in GaP

“…Understanding of the underlying mechanisms of THz generation and detection is a key requirement for optimization of THz systems. Although solving a nonlinear coupled-wave equation is generally required to fully describe the THz generation process [31,32], according to our measurements, the THz spectrum can be reasonably approximated by decoupled multiplicative factors in the frequency domain. This approach provides a simple tool to isolate the influence of different parameters and determine the key limitations.…”

Broadband terahertz wave generation from an epsilon-near-zero material

“…THz radiation can be generated through the nonlinear downconversion of optical signals or through the nonlinear upconversion of microwave signals, among which the nonlinear optical rectification method is particularly popular for the generation of broadband THz pulses for spectroscopy-related applications. Despite the recent discoveries of broadband THz generation in air plasma 12 , 13 and liquids 14 , THz emission is more routinely generated by pumping solid-state noncentrosymmetric nonlinear crystals, such as ZnTe 15 , GaP 16 , and LiNbO 3 17 , with a femtosecond laser typically operating in the near-infrared range. However, the intensity and bandwidth of the generated THz signal, as well as the pump wavelength, are often limited by the phase-matching condition in the bulk nonlinear crystal.…”