Continuous ultraviolet to blue-green astrocomb.

Cosmological and exoplanetary science using transformative telescopes like the ELT will demand precise calibration of astrophysical spectrographs in the blue-green, where stellar absorption lines are most abundant. Astrocombs-lasers providing a broadband sequence of regularly-spaced optical frequencies on a multi-GHz grid-promise an atomically-traceable calibration scale, but their realization in the blue-green is challenging for current infrared-laser-based technology. Here, we introduce a concept achieving a broad, continuous spectrum by combining second-harmonic generation and sum-frequency-mixing in an MgO:PPLN waveguide to generate 390-520 nm light from a 1 GHz Ti:sapphire frequency comb. Using a Fabry-Pérot filter, we extract a 30 GHz sub-comb spanning 392-472 nm, visualizing its thousands of modes on a high-resolution spectrograph. Experimental data and simulations demonstrate how the approach can bridge the spectral gap present in second-harmonic-only conversion. Requiring only [Formula: see text]100 pJ pulses, our concept establishes a new route to broadband UV-visible generation at GHz repetition rates.

Feed-forward stabilization of a single-frequency, diode-pumped Pr:YLF-Cr:LiCAF laser operating at 813.42†nm.

We introduce a simple and compact diode-pumped Pr:YLF-Cr:LiCAF laser, operating at 813.42 nm and providing a 130-mW, single-frequency output tunable over a 3-GHz range. The laser has a short-term intrinsic linewidth estimated to be 700 Hz (ß-separation method), while exhibiting a free-running wavelength stability of below 1 pm in one hour. Using a feed-forward technique we demonstrate the integration of the laser output into a fully stabilized, 1-GHz Ti:sapphire laser frequency comb, resulting in a heterodyne beat note between the laser and the comb with a bandwidth of 65 kHz. Combining feed-forward control with a low-bandwidth servo feedback loop permits stable long-term locking with an rms beat note variation of 15 kHz over 2 minutes. This performance makes the laser a potential candidate for the lattice laser in a 87Sr optical lattice clock.

Dither-free stabilization of a femtosecond doubly resonant OPO using parasitic sum-frequency mixing.

Stable operation of a doubly resonant femtosecond optical parametric oscillator (OPO) requires submicron matching of the OPO and pump laser cavity lengths, which is normally implemented using a dither-locking feedback scheme. Here we show that parasitic sum-frequency mixing between the pump and resonant pulses of a degenerate femtosecond OPO provides an error signal suitable for actuating the cavity length with the precision needed to maintain oscillation on a single fringe and at maximum output power. Unlike commonly used dither-locking approaches, the method introduces no modulation noise and requires no additional optical components, except for one narrowband filter. The scheme is demonstrated on a Ti:sapphire-pumped sub-40-fs PPKTP OPO, from which data are presented showing a tenfold reduction in relative intensity noise compared with dither locking.