Abstract
The angular dependence of terahertz (THz) emission from birefringent crystals can differ significantly from that of cubic crystals. Here we consider optical rectification in uniaxial birefringent materials, such as chalcopyrite crystals. The analysis is verified in (110)-cut ZnGeP_2 and compared to (zincblende) GaP. Although the crystals share the same nonzero second-order tensor elements, the birefringence in chalcopyrite crystals cause the pump pulse polarization to evolve as it propagates through the crystal, resulting in a drastically different angular dependence in chalcopyrite crystals. The analysis is extended to {012}- and {114}-cut chalcopyrite crystals and predicts more efficient conversion for the {114} crystal cut over the {012}- and {110}-cuts.
Highlights
Advances in broadband terahertz (THz) pulse generation by optical rectification have led to significant increases in available pulse energies, applicable for communications [1], imaging and spectroscopy [2], coherent control [3], and chemical recognition [4]
To make full use of various nonlinear optical crystals for broadband THz generation, it is useful to explore the effects of birefringence on optical rectification in uniaxial and biaxial materials
The experimental and modeled results performed here show that birefringence modifies the angular dependence of the THz emission compared to the zincblende binary analogs
Summary
Advances in broadband terahertz (THz) pulse generation by optical rectification have led to significant increases in available pulse energies, applicable for communications [1], imaging and spectroscopy [2], coherent control [3], and chemical recognition [4]. To make full use of various nonlinear optical crystals for broadband THz generation, it is useful to explore the effects of birefringence on optical rectification in uniaxial and biaxial materials. A previous comparative study [7] of the THz emission amplitude from ZGP, GaP, and GaAs showed ZGP to have suitable characteristics for excitation by near-infrared sources such as pulsed-fiber or chromium-doped forsterite lasers. It has a 2% lattice compression in the [001] direction, producing significant birefringence. The work presented here explores the orientation dependence of uniaxial birefringent chalcopyrite crystals in order to optimize the phase-matching condition and build understanding of the optical rectification process. The analysis is extended to other crystal orientations to demonstrate optimization of the effective nonlinear coefficient
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