Feedback control of optical beam spatial profiles using thermal lensing

Abstract

A method for active control of the spatial profile of a laser beam using adaptive thermal lensing is described. A segmented electrical heater was used to generate thermal gradients across a transmissive optical element, resulting in a controllable thermal lens. The segmented heater also allows the generation of cylindrical lenses, and provides the capability to steer the beam in both horizontal and vertical planes. Using this device as an actuator, a feedback control loop was developed to stabilize the beam size and position.

Squeezed light for advanced gravitational wave detectors and beyond

“…We quantified the contributions from each of these imperfections to the overall performance of a gravitational wave detector like Advanced LIGO, and we show how an in-vacuum OPO, together with an improved control scheme can minimize the impact of all of these noise sources. Housing the OPO in vacuum, using the OMC transmission to derive a better error signal for quadrature fluctuations, and introducing additional alignment and mode-matching control [29,30,35] will also increase the operational reliability of the squeezed light source. These proposed solutions, when coupled with quantum noise filter cavities [15], promise to deliver up to 10 dB of squeezing enhancement across a broad range of frequencies critical to future gravitational wave detectors.…”

“…However, several techniques to reduce optical losses are currently under investigation. The light coupling through the OMC can be improved by actively controlling the mode matching [29,30], and a similar approach can be used to mode match the squeezed beam to the interferometer. Moreover, studies of scatter losses in fused silica optics and resonant cavities can be used to maximize the throughput of the Faradays isolators and the OMC [31,32].…”

Progress and challenges in advanced ground-based gravitational-wave detectors

“…In-air tests of an initial prototype have shown a dynamic range of up to −100 mD focal power [34]. Use of the actuator in a beam-shape feedback control loop was also demonstrated [35]. An advanced prototype has recently been tested in vacuum, with a demonstrated dynamic range up to −50 mD focal power.…”

Sensing optical cavity mismatch with a mode-converter and quadrant photodiode

“…The beam then passes through a 25 MHz EOM for PDH locking and wave front sensing. The phase modulated beam propagates to mode matching lenses and then to a four segment thermal lens actuator [13][14][15]. A telescope is built around the thermal lens actuator such that the beam spot size is as big as possible without clipping on the 1 inch optic.…”