A high-finesse Fabry-Perot cavity with a frequency-doubled green laser for precision Compton polarimetry at Jefferson Lab

TL;DR

This paper reports the development of a high-finesse Fabry-Perot cavity using a frequency-doubled green laser for precise electron beam polarization measurements at Jefferson Lab, achieving high power enhancement and low polarization uncertainty.

Contribution

The paper introduces a novel high-finesse cavity system with a green laser, enabling high-precision Compton polarimetry with significant power enhancement and measurement accuracy.

Findings

Achieved 1.74 W green laser power with 34.8% efficiency.

Enhanced intra-cavity power up to 3.7 kW with a factor of 3800.

Measured polarization transfer with 0.7% uncertainty.

Abstract

A high-finesse Fabry-Perot cavity with a frequency-doubled continuous wave green laser (532~nm) has been built and installed in Hall A of Jefferson Lab for high precision Compton polarimetry. The infrared (1064~nm) beam from a ytterbium-doped fiber amplifier seeded by a Nd:YAG nonplanar ring oscillator laser is frequency doubled in a single-pass periodically poled MgO:LiNbO$_{3}$ crystal. The maximum achieved green power at 5 W IR pump power is 1.74 W with a total conversion efficiency of 34.8\%. The green beam is injected into the optical resonant cavity and enhanced up to 3.7~kW with a corresponding enhancement of 3800. The polarization transfer function has been measured in order to determine the intra-cavity circular laser polarization within a measurement uncertainty of 0.7\%. The PREx experiment at Jefferson Lab used this system for the first time and achieved 1.0\% precision in polarization measurements of an electron beam with energy and current of 1.0~GeV and 50~$\mu$A.