M. C. Heintze

The advanced LIGO input optics

The advanced LIGO gravitational wave detectors are nearing their design sensitivity and should begin taking meaningful astrophysical data in the fall of 2015. These resonant optical interferometers will have unprecedented sensitivity to the strains caused by passing gravitational waves. The input optics play a significant part in allowing these devices to reach such sensitivities. Residing between the pre-stabilized laser and the main interferometer, the input optics subsystem is tasked with preparing the laser beam for interferometry at the sub-attometer level while operating at continuous wave input power levels ranging from 100 mW to 150 W. These extreme operating conditions required every major component to be custom designed. These designs draw heavily on the experience and understanding gained during the operation of Initial LIGO and Enhanced LIGO. In this article, we report on how the components of the input optics were designed to meet their stringent requirements and present measurements showing how well they have lived up to their design.

Achieving resonance in the Advanced LIGO gravitational-wave interferometer

Interferometric gravitational-wave detectors are complex instruments comprised of a Michelson interferometer enhanced by multiple coupled cavities. Active feedback control is required to operate these instruments and keep the cavities locked on resonance. The optical response is highly nonlinear until a good operating point is reached. The linear operating range is between 0.01% and 1% of a fringe for each degree of freedom. The resonance lock has to be achieved in all five degrees of freedom simultaneously, making the acquisition difficult. Furthermore, the cavity linewidth seen by the laser is only _(~1) Hz, which is four orders of magnitude smaller than the linewidth of the free running laser. The arm length stabilization system is a new technique used for arm cavity locking in Advanced LIGO. Together with a modulation technique utilizing third harmonics to lock the central Michelson interferometer, the Advanced LIGO detector has been successfully locked and brought to an operating point where detecting gravitational-waves becomes feasible.

Thermal effects in the Input Optics of the Enhanced Laser Interferometer Gravitational-Wave Observatory interferometers.

Katherine L. Dooley, a) Muzammil A. Arain, b) David Feldbaum, Valery V. Frolov, Matthew Heintze, Daniel Hoak, c) Efim A. Khazanov, Antonio Lucianetti, d) Rodica M. Martin, Guido Mueller, Oleg Palashov, Volker Quetschke, e) David H. Reitze, f) R. L. Savage, D. B. Tanner, Luke F. Williams, and Wan Wu g) University of Florida, Gainesville, FL 32611, USA LIGO Livingston Observatory, Livingston, LA 70754, USA Institute of Applied Physics, Nizhny Novgorod 603950, Russia LIGO Hanford Observatory, Richland, WA 99352, USAWe present the design and performance of the LIGO Input Optics subsystem as implemented for the sixth science run of the LIGO interferometers. The Initial LIGO Input Optics experienced thermal side effects when operating with 7 W input power. We designed, built, and implemented improved versions of the Input Optics for Enhanced LIGO, an incremental upgrade to the Initial LIGO interferometers, designed to run with 30 W input power. At four times the power of Initial LIGO, the Enhanced LIGO Input Optics demonstrated improved performance including better optical isolation, less thermal drift, minimal thermal lensing, and higher optical efficiency. The success of the Input Optics design fosters confidence for its ability to perform well in Advanced LIGO.

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).

Small optic suspensions for Advanced LIGO input optics and other precision optical experiments

We report on the design and performance of small optic suspensions developed to suppress seismic motion of out-of-cavity optics in the input optics subsystem of the Advanced Laser Interferometer Gravitational Wave Observatory. These compact single stage suspensions provide isolation in all six degrees of freedom of the optic, local sensing and actuation in three of them, and passive damping for the other three.

Development of a 1.5μm Er:Yb:glass laser for use in a Coherent Laser Radar

We describe an injection-seeded Q-switched Er:Yb:glass laser that uses a novel resonator and produces transform-limited 500 ns pulses. Experimental results of the laser performance and its suitability for use in coherent laser radar will be presented.

Eye safe solid state lasers for remote sensing and coherent laser radar

This study demonstrates a second generation version of a three-level injection seeded Er:glass laser that works as a transform limited coherent laser radar. This laser is designed to maximize the average power that can be extracted from a bulk glass host. It uses pulsed pump diode lasers and a conduction cooled, co-planar folded zig-zag slab (CPFS) gain medium in an injection seeded, long Q switched pulsed configuration. This laser can operate at 60 mJ per pulse at 10 Hz in a standing wave configuration. For eye-safe operation it should not exceed 10 mJ per pulse. The resonator used in this work is developed specifically for generating long pulse, single frequency Q-switched outputs in low gain laser media. This work describes the latest results of this prototype laser and its properties for coherent single frequency sensing. A design for a third generation of this laser are also be discussed.