Tunable spectral squeezers based on monolithically integrated diamond Raman resonators

Abstract

We report on the generation and tuning of single-frequency laser light in a monolithic Fabry–Pérot diamond Raman resonator operating in the visible spectral range. The device was capable of squeezing the linewidth of a broad multi-mode nanosecond pump laser (Δνp= 7.2 ± 0.9 GHz at λp= 450 nm) to a nearly Fourier-limited single axial mode Stokes pulse (ΔνS= 114 ± 20 MHz at λS= 479 nm). The tuning was achieved by precise adjustment of the resonator temperature, with a measured frequency-temperature tuning slope of ∂ν0/∂T≈ −3 GHz/K, and a temperature dependence of the first-order Raman phonon line of ∂νR/∂T≈ +0.23 GHz/K. The Stokes center frequency was tuned continuously for over 20 GHz (more than twice the free spectral range of the resonator), which, in combination with the broad Ti:Sapphire laser spectral tunability, enables the production of Fourier-limited pulses in the 400–500 nm spectral range. The Stokes center-frequency fluctuations were 52 MHz (RMS) when the temperature of the resonator was actively stabilized. Moreover, the conversion efficiency was up to 30%, yielding an overall power spectral density enhancement of >25× from pump to Stokes pulse.