Narrowband, tunable, infrared radiation by parametric amplification of a chirped backward-wave OPO signal

Abstract

The strict momentum conservation constraints for backward-wave optical parametric oscillators (BWOPOs) gives an inherently narrowband backward-generated wave, even with broadband pumping. Unfortunately, the limited tuning range of this wave restricts potential applications. Here we demonstrate a method to circumvent this restriction and increase the tuning range by more than one order of magnitude. A linearly chirped pump modulation is transferred to the forward-generated BWOPO wave, which is then mixed with an identically chirped pump in a conventional optical parametric amplifier to obtain narrowband (38 GHz), broadly tunable, infrared radiation around 1.86 µm, with an output energy of 19 µJ.

Coherent phase transfer and pulse compression at 14 μm in a backward-wave OPO

“…The pulses were polarized along the c-axis of the crystal and propagated along its a-axis to exploit the largest nonlinearity of the crystal (d 33 coefficient). The BWOPO threshold was reached at a pump intensity of 0.72 GW∕cm 2 , and the conversion efficiency obtained was 42% at a maximum pump energy of 196 μJ [8].…”

“…At the pump energy of 196 μJ, the bandwidth of the depleted pump was measured to be 1.88 THz, while the generated signal at 1.4 μm had a bandwidth of about 1.91 THz [8]. The corresponding bandwidth of the backward idler wave was 28 GHz.…”

“…Moreover, optical frequency translators are mostly realized in waveguide structures with lower achievable powers. Single-pass BWOPOs can easily provide μJ energies for the near-IR frequency translated bandwidths [2,8] and the accessible wavelength range is much broader, thanks to the tuning capabilities of the forward wave with respect to the pump.…”

“…where β 1,p and β 1,b represent the inverse group velocities for the pump and backward waves, respectively, for a QPM grating of length L. The forward wave will get a pulse duration of the same order of magnitude as that of the pump, and should carry the same chirp [8].…”

Backward optical parametric oscillator threshold and linewidth studies

“…In [2], the authors also validated the unique spectral properties of the light emitted by the BWOPO, in which the spectral bandwidth of the pump wave is basically transferred to the forward wave while the backward wave exhibits a narrow spectral linewidth. These spectral properties have then been extensively investigated through experimental and numerical studies in pulsed regime and exploited to carry out coherent phase transfer from the pump wave to the signal wave [3][4][5][6].…”