Characterization of non-planar ring oscillators at a wavelength of 1064 nm for high precision metrology

TL;DR

This study addresses the need for ultra-low-noise seed lasers at 1064 nm for high-precision metrology and gravitational-wave detectors by benchmarking a newly developed in-house NPRO against two commercial devices. Using a three-part experimental setup, the authors measure relative power noise and frequency noise, then scale to high power with a solid-state Nd:YVO$_4$ amplifier while assessing noise propagation. The AEI NPRO consistently shows more than an order of magnitude lower noise, with effective internal noise reduction and favorable coupling characteristics between pump power fluctuations and emission frequency. The results demonstrate that the low-noise seed can drive high-power systems (up to ~40 W) without significant degradation in frequency noise or beam quality, offering a practical path to improved sensitivity in GW detectors and related precision experiments.

Abstract

Ultra-stable laser light is essential for high-precision interferometric measurements, in particular for the next generation of gravitational wave detectors, where high power lasers with unprecedented low power and frequency noise are demanded. Since the seed laser for high-power laser system has a large influence on the overall noise characteristics, the use of the lowest noise seed laser is beneficial. This study compares a newly developed seed laser, based on a non-planar ring oscillator (NPRO) design, at a wavelength of 1064 nm with two commercial NPROs and shows that the new laser exhibits ten times lower power and frequency noise. This noise advantage is retained even after subsequent amplification to 40 W.

Figures (8)

• Figure 1: The experimental setup consists of three parts. On the left side, the NPRO lasers under test are located, along with a reference laser for individual NPRO power noise and laser frequency noise measurements. In the middle of the setup, the laser amplification stage is illustrated, where the amplified laser beam is generated. On the right side, the power stabilization and diagnostics setup for the amplified laser beam is shown.
• Figure 2: A comparison of the relative power noise of three NPRO-based laser sources. In (a) the measurements without laser internal noise reduction are shown, whereas the results with the laser internal noise suppression engaged are presented in (b). To ensure that the out-of-loop measurements were not limited by photon shot noise or electronic dark noise, an in-house made high-power and low-noise photo detector was used.
• Figure 3: Frequency noise of the NPRO lasers derived from beat note measurements, with all measurements taken with the internal noise reduction of the lasers engaged. Notably, the AEI NPRO laser achieved an even lower frequency noise level when operated at 250 output power (LP).
• Figure 4: The pump-current-to-emission-power transfer function was measured for the AEI NPRO laser, showing a resonant enhancement around the relaxation oscillation and a decay above it (red trace). Additionally, the pump-power-to-emission-frequency transfer function was measured using the beat note between two AEI NPRO lasers and a phase meter (blue trace).
• Figure 5: The absolute laser frequency, captured with a wavemeter instrument, and the laser frequency thermal tuning range of the AEI NPRO is illustrated. The characteristic mode hops, where another free spectral range of the NPRO gains the highest cross section with the optical gain, can be observed every 3.