Optical lock-in camera for gravitational wave detectors.

Knowledge of the intensity and phase profiles of spectral components in a coherent optical field is critical for a wide range of high-precision optical applications. One of these is interferometric gravitational wave detectors, which rely on the optical beats between these fields for precise control of the experiment. Here we describe an optical lock-in camera and show that it can be used to record optical beats at MHz or greater frequencies with higher spatial and temporal resolution than previously possible. This improvement is achieved using a Pockels cell as a fast optical switch to transform each pixel on a sCMOS array into an optical lock-in amplifier. We demonstrate that the optical lock-in camera can record fields with 2 Mpx resolution at 10 Hz with a sensitivity of -62 dBc when averaged over 2s.

Enhancing the dynamic range of deformable mirrors with compression bias.

We report the design and testing of a compression-biased thermally-actuated deformable mirror that has a dynamic range larger than the limit imposed by pure-bending stress, negligible higher-order-mode scattering, and a linear defocus response and that is vacuum compatible. The optimum design principles for this class of actuator are described and a mirror with 370 mD dynamic range is demonstrated.

High dynamic range thermally actuated bimorph mirror for gravitational wave detectors.

Adaptive optics are crucial for overcoming the fabrication limits on mirror curvature in high-precision interferometry. We describe a low-cost thermally actuated bimorph mirror with 200 mD linear response, which meets dynamic range and low aberration requirements for the ${\rm{A}} + $A+ upgrade of the Laser Interferometer Gravitational-wave Observatory (LIGO). Its deformation and operation limits were measured and verified against finite element simulation.

Short-pulse actively Q-switched Er:YAG lasers.

We report the shortest duration pulses obtained to date from an actively Q-switched Er:YAG laser pumped by a low spectral and spatial brightness laser diode. The 14.5 ns, 6 mJ pulses were obtained using a 1470 nm laser diode end-pumped co-planar folded zigzag slab architecture. We also present an analytical model that accurately predicts the pulse energy-duration product achievable from virtually all Q-switched Er:YAG lasers and high repetition rate quasi-three-level Q-switched lasers in general.

Single-pulse measurement of wind velocities using an Er:Yb:glass coherent laser radar.

Many wind-field mapping applications require range-resolved atmospheric velocity measurements at long range and/or with a temporal resolution sufficient to investigate turbulence. We argue that this capability can be achieved only by coherent laser radar systems that transmit energetic (>1 mJ) pulses. We describe such a system and describe single-pulse measurement of the range-resolved line-of-sight velocities, and show that the instrument-limited reproducibility of the measurements is 0.4 ms(-1).

Direct measurement of absorption-induced wavefront distortion in high optical power systems.

Wavefront distortion due to absorption in the substrates and coatings of mirrors in advanced gravitational wave interferometers has the potential to compromise the operation and sensitivity of these interferometers [Opt. Lett.29, 2635-2637 (2004)]. We report the first direct spatially-resolved measurement, to our knowledge, of such wavefront distortion in a high optical power cavity. The measurement was made using an ultrahigh sensitivity Hartmann wavefront sensor on a dedicated test facility. The sensitivity of the sensor was lambda/730, where lambda=800 nm.

Injection mode-locked guide star laser concept and design verification experiments.

Injection mode-locking combined with stretched Q-switching of a ring resonator are proposed and demonstrated as a promising approach for advanced, guide star lasers. The concept uses two Nd:YAG lasers, producing a macro-micro pulse-burst output, optimized for efficient sum-frequency generation. We demonstrate wavelength, bandwidth and timing control required to maximize the atmospheric Na fluorescence.

Ultra-sensitive wavefront measurement using a Hartmann sensor.

We describe a Hartmann sensor with a sensitivity of lambda /15,500 at lambda= 820nm. We also demonstrate its application to the measurement of an ultra small change in wavefront and show that the result agrees with that expected to within lambda/3,300.

Fast rise time, long pulse width, kilohertz repetition rate Q-switch driver.

We describe a versatile Pockels cell Q-switch driver that can generate high voltage electrical pulses having both fast rise times and long duration, with a repetition rate in excess of 1 kHz. The circuit is simple and easily adaptable to most types of Q-switched lasers and regenerative amplifiers.

Accurate and precise optical testing with a differential Hartmann wavefront sensor.

A novel differential Hartmann sensor is described. It can be used to determine the characteristics of an optic accurately, precisely, and simply without detailed knowledge of the wavefront used to illuminate the optical system or of the geometry of the measurement system. We demonstrate the application of this sensor to both zonal and modal optical testing of lenses. We also describe a dual-camera implementation of the sensor that would enable high-speed optical testing.

Thermally induced birefringence in Nd:YAG slab lasers.

We study thermally induced birefringence in crystalline Nd:YAG zigzag slab lasers and the associated depolarization losses. The optimum crystallographic orientation of the zigzag slab within the Nd:YAG boule and photoelastic effects in crystalline Nd:YAG slabs are briefly discussed. The depolarization is evaluated using the temperature and stress distributions, calculated using a finite element model, for realistically pumped and cooled slabs of finite dimensions. Jones matrices are then used to calculate the depolarization of the zigzag laser mode. We compare the predictions with measurements of depolarization, and suggest useful criteria for the design of the gain media for such lasers.