Vibration Property of a Cryogenic Optical Resonator within a Pulse-Tube Cryostat

Cryogenic ultrastable laser cavities push laser stability to new levels due to their lower thermal noise limitation. Vibrational noise is one of the major obstacles to achieve a thermal-noise-limited cryogenic ultrastable laser system. Here, we carefully analyze the vibrational noise contribution to the laser frequency. We measure the vibrational noise from the top of the pulse-tube cryocooler down to the experiment space. Major differences emerge between room and cryogenic temperature operation. We cooled a homemade 6 cm sapphire optical resonator down to 3.4 K. Locking a 1064 nm laser to the resonator, we measure a frequency stability of 1.3×10−15. The vibration sensitivities change at different excitation frequencies. The vibrational noise analysis of the laser system paves the way for in situ accurate evaluation of vibrational noise for cryogenic systems. This may help in cryostat design and cryogenic precision measurements.

Phase Compensation Method in OPA System Based on the Linear Electro-Optic Effect

Factors such as mechanical deformation and temperature changes lead to phase mismatch in optical parametric amplification systems, impacting energy stability. A phase compensation method via the linear electro-optic effect can overcome this limitation. Phase mismatch compensation characteristics were simulated via the linear electro-optic effect in 70%-deuterated DKDP and 95%-deuterated DKDP. This method was applied to OPA systems to verify its feasibility. The results show that the temperature acceptance bandwidth of 70%-deuterated DKDP and 95%-deuterated DKDP can be ~1.75 and ~2 times larger, respectively, than that of the OPA without compensation. Moreover, the angle acceptance bandwidth of 70%-deuterated DKDP and 95%-deuterated DKDP can be ~2 times larger than that of the OPA without compensation. The abovementioned method can facilitate the compensation of phase mismatch within a range and can be widely used in OPA and optical parametric chirped pulse amplification systems to improve laser stability.

Multifunctional contamination-resistant coatings

Surface contaminations can critically affect the performance of optical surfaces, in particular with respect to light scattering, optical losses, and laser stability. Thus, avoiding contaminations and reducing contamination-induced effects is of particular interest in the manufacturing of optical systems. By combining a specific thin film design with a tailored structural design, contamination-resistant coatings with a high optical quality can be realized. Most important is the balance of self-cleaningand light scattering-relevant surface roughness components.