Intracavity Terahertz Generation in a Synchronously Pumped Optical Parametric Oscillator Using Quasi-Phasematched GaAs

Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305, USA.
Optics Letters (Impact Factor: 3.29). 06/2007; 32(10):1284-6. DOI: 10.1364/OL.32.001284
Source: PubMed


We generated 1 mW of average output power at 2.8 THz (bandwidth of approximately 300 GHz) in a diffraction-limited beam by placing a 6-mm-long quasi-phase-matched GaAs crystal inside the cavity of a synchronously pumped optical parametric oscillator (OPO). The OPO used type-II-phase-matched periodically poled lithium niobate as a gain medium and was pumped by a mode-locked laser at 1064 nm, with a 7 ps pulse duration, 50 MHz repetition rate, and 10 W average output power. The terahertz radiation was generated by difference frequency mixing between the signal and idler waves of the near-degenerate doubly resonant OPO.

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    • "K. Saito et al. tion because of their unique features, such as high transmittance through non-metallic materials, low photon energies that correspond to thermal energies of room temperature and weak molecular bonding, especially the hydrogen bonding. These features can be applied for non-destructive inspection, label-free identification of biomolecules , environmental polluting gas monitoring, and high speed wireless communication, etc. [1]-[3]. Monochromatic THz sources based on the nonlinear optical (NLO) effect such as optical parametric oscillation and difference-frequency generation (DFG) are promising methods due to their characteristic features such as high power, widely tuneable frequency and room temperature operation. "
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    • "In previous work[ref], a QPM-GaAs crystal was placed inside a near-degenerate, doubly resonant periodically poled lithium niobate (PPLN) based OPO. Designs using type-II interactions (signal and idler perpendicular, pump polarized parallel to signal) in an offset linear cavity[2], and type-0 (all polarizations parallel) in a ring cavity [3] have been used in the past. While the type-0 design allows access to the higher nonlinear coefficient of PPLN and lower roundtrip loss, the broad acceptance bandwidth near degeneracy makes single line pair (signal and idler) operation difficult. "
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    ABSTRACT: sonant cavity enhancement results in substantial improvement in the efficiency of photonic THz-wave generation via difference frequency generation (DFG). A nearly degenerate optical parametric oscillator (OPO) was pumped by 6 ps pulses at 1064 nm, producing signal and idler pulses with average total power in excess of 80 W. By placing a sample of quasi-phasematched gallium arsenide (QPM-GaAs) at a focus of a ring cavity OPO, multicycle, narrowband THz radiation was produced, with average powers in excess of 100 μW and peak powers exceeding 150 mW. The dependence of the THz power on pump power shows no signs of saturation, so with higher power pump lasers, mW levels of average THz should be obtainable.
    Full-text · Article · Feb 2012 · Proceedings of SPIE - The International Society for Optical Engineering
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    • "Digital Object Identifier 10.1109/LPT.2008.2008195 DFG has also been used to generate THz using solid-state -switched lasers as a pump source, and have high-power and narrow linewidth THz [7], [12], [13]. However, solid-state lasers tend to be bulky, and require free space cavity alignment, compared to QCLs and fiber lasers. "
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    ABSTRACT: We report a high-power single-frequency fiber laser system in the eyesafe wavelength region that pumps a GaSe crystal through difference frequency generation, producing narrowband terahertz (THz). Two single-frequency continuous-wave fiber seed lasers are modulated, then amplified with a three-stage single-mode amplifier. The resulting pulses are transform-limited and high power, producing a peak THz power of 26.4 mW with narrow linewidth. This is significantly higher than earlier THz sources based on narrowband fiber lasers in the eyesafe region.
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