Ultrastable lasers based on vibration insensitive cavities (0901.4717v3)

Abstract: We present two ultra-stable lasers based on two vibration insensitive cavity designs, one with vertical optical axis geometry, the other horizontal. Ultra-stable cavities are constructed with fused silica mirror substrates, shown to decrease the thermal noise limit, in order to improve the frequency stability over previous designs. Vibration sensitivity components measured are equal to or better than 1.5e-11 per m.s^-2 for each spatial direction, which shows significant improvement over previous studies. We have tested the very low dependence on the position of the cavity support points, in order to establish that our designs eliminate the need for fine tuning to achieve extremely low vibration sensitivity. Relative frequency measurements show that at least one of the stabilized lasers has a stability better than 5.6e-16 at 1 second, which is the best result obtained for this length of cavity.

Overview of Ultra-Stable Lasers Based on Vibration Insensitive Cavities

This paper presents significant advancements in the design and implementation of ultra-stable lasers through the development of two novel optical cavities. These cavities, described as horizontal and vertical configurations, are engineered to achieve minimal vibration sensitivity by leveraging specific geometries and materials. The primary objective is to enhance the frequency stability of lasers for various applications in precision measurement, including optical frequency standards and gravitational wave detection.

Key Findings

The authors introduce two optical cavities with distinct axes: horizontal and vertical. Both cavities are designed with a focus on mitigating the effects of mechanical vibrations and thermal noise, which are critical factors in maintaining laser frequency stability. The most innovative aspect of the cavities is the inclusion of fused silica mirror substrates, selected for their higher mechanical Q factor, providing a noteworthy reduction in thermal noise compared to all-Ultra Low Expansion (ULE) glass designs. This reduction is quantified as having a thermal noise floor estimated at approximately $4 \times 10^{-16}$, primarily due to the minimized thermal noise from the mirrors’ coating.

Vibration sensitivity measurements reveal impressive results, showing components equal to or better than $1.5 \times 10^{-11}$ (m\,s$^{-2}$)$^{-1}$ across all spatial directions, with the vertical cavity achieving an unprecedented sensitivity below this threshold for prior designs. Most notably, the horizontal cavity demonstrates a low dependence on support point positions, eliminating the laborious fine-tuning process typically required.

Experimental Methodology and Results

Finite element simulations play a critical role in the design process, where the authors examined the effects of mirror displacement, considering translation and tilt due to acceleration. The vertical cavity exhibits minimal vibration sensitivity due to its symmetrical support configuration, while the horizontal cavity benefits from meticulously optimized support points that ensure minimal vibration sensitivity and thermal noise.

Experiments involve stabilizing two lasers to the distinct cavities and comparing the frequency stability through a beat-note measurement. The beat-note reveals a relative frequency stability better than $5.6 \times 10^{-16}@1s$, establishing this as the most stable laser for its cavity length and compact design. This exceptional stability underscores the practical prospects of employing such laser systems in future applications demanding high precision and stability.

Implications and Future Directions

The findings have substantive implications for the development of optical frequency standards and precision timekeeping, possibly approaching the quantum-limit imposed Dick effect by enhancing laser frequency stability. The paper underscores the potential benefits of employing fused silica mirrors in other cavity designs, which could lead to further improvements in laser stability and open avenues for more compact and robust laser systems suitable for applied technological environments.

In theoretical contexts, the paper propels further analysis into vibration and thermal noise effects on cavity designs, suggesting a direction towards integrating composite materials and more refined geometrical optimizations. Future research might explore the interplay between cavity geometry and alternative materials or hybrid systems to achieve even greater frequency stability and game-changing applications in physics, engineering, and beyond.