Self calibrating wavelength multiplexed heterodyne interferometer for angstrom precision measurements

Measurement of refractive index, surface quality and temperature of the process materials in defense, petrochemical, power systems, glass, and metal industries is a fundamental need for precision systems performance. However, making these measurements in a super noisy defense or industrial environment is a big challenge faced by sensor technologies. Reported in this paper is the first ever demonstration of a wavelength multiplexed heterodyne interferometer using a single acousto-optic device (AOD). Heterodyne interferometry is pivotal in realizing a highly stable low noise interferometer. Inspite of the physical separation of the two arms of the interferometer, the sensor demonstrates Angstrom level optical path length sensitivity. The proposed sensor can be used in optical path length measurement-based sensing of parameters such as surface profile, refractive index, temperature, and pressure. Proof-of-concept experiment features a high resolution, low-loss, ultra compact, free space scanning interferometer implementation. Results include measurement of surface quality of a test mirror

High-beamforming power code multiplexed optical scanner for three dimensional displays.

Three dimensional (3-D) displays play an important role in the field of entertainment. Today, research is being conducted to produce 3-D displays to meet the complex needs of high-functionality full motion 3D displays at reasonable cost, but without glasses, complicated viewing arrangements or restricted fields of view. Other applications for 3-D displays include but are not limited to CAD/Design simulation, advanced data representation, displaying complex 3-D information for automotive design, medical imaging, advanced navigation displays, scientific visualization, and advertising. The key element in all these applications is an optical beam scanner that can display 3-D images for large viewing angles. Our proposed Code Multiplexed Optical Scanner (C-MOS) can fulfill all these requirements with its high beamforming power capabilities. Our proposed experiment demonstrates three dimensional (3-D) beam scanning with large angles (e.g., >160(0)), large centimeter size aperture, and scanning speed of 160(0)), large centimeter size aperture, and scanning speed o

Ultrafast optical tomography systems using coherence agility.

Described are three types of optical imaging systems based on source coherence agility. On axis ultrafast microsecond sub-surface imaging is achieved by use of a broadband low coherence optical source to implement fast Doppler time domain optical coherence tomography (OCT). Ibis system is formed as a combination of a fast scan acousto-optically implemented variable optical delay line with a single acousto-optic (AO) Bragg cell optical heterodyne interferometer. A second imaging system is introduced with a no-moving parts probe design and fast microsecond speed optical spatial scanning along one dimension implemented using a fixed wavelength high coherence source with a single Bragg cell AO interferometer. The third design involves realization of a spectral domain OCT system implemented via the use of a tunable laser in the proposed single AO cell heterodyne interferometer.Described are three types of optical imaging systems based on source coherence agility. On axis ultrafast microsecond sub-surface imaging is achieved by use of a broadband low coherence optical source to implement fast Doppler time domain optical coherence tomography (OCT). Ibis system is formed as a combination of a fast scan acousto-optically implemented variable optical delay line with a single acousto-optic (AO) Bragg cell optical heterodyne interferometer. A second imaging system is introduced with a no-moving parts probe design and fast microsecond speed optical spatial scanning along one dimension implemented using a fixed wavelength high coherence source with a single Bragg cell AO interferometer. The third design involves realization of a spectral domain OCT system implemented via the use of a tunable laser in the proposed single AO cell heterodyne interferometer

Overview of Advanced LIGO Adaptive Optics

This is an overview of the adaptive optics used in Advanced LIGO (aLIGO), known as the thermal compensation system (TCS). The thermal compensation system was designed to minimize thermally-induced spatial distortions in the interferometer optical modes and to provide some correction for static curvature errors in the core optics of aLIGO. The TCS is comprised of ring heater actuators, spatially tunable CO$_{2}$ laser projectors and Hartmann wavefront sensors. The system meets the requirements of correcting for nominal distortion in Advanced LIGO to a maximum residual error of 5.4nm, weighted across the laser beam, for up to 125W of laser input power into the interferometer

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

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

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

We 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

Sub-Micron Range Thickness Measurements Using A Novel Scanning Heterodyne Optical Interferometer

In this paper, we introduce a novel and highly accurate method of thickness measurement using a compact, high performance, scanning heterodyne optical interferometer. The instrument has the potential to measure thickness at an Angstrom resolution over a micron continuous thickness range. The instrument uses acousto-optic devices to implement rapid scanning for thickness measurements of the test medium. As the read optical beams scan the test medium for thickness assessment, the double Bragg diffraction makes the final interfering output beam stationary on the two high speed photo-detectors used for radio frequency signal generation via heterodyne detection. When a test medium is introduced in the read beam, an additional phase shift 2π t (n-1) / λ appears in the read beam as compared to the reference beam where t, n and λ, are the thickness, refractive index and wavelength of the laser beam, respectively. This phase difference gives the thickness of the medium. Mechanical vibrations and thermal noise are eliminated via use of common optical and rf paths. A reflective design of the interferometer results in a compact and low component count instrument. Experimental results are reported using the novel interferometer and instrument issues are discussed

Programmable Broadband Radio-Frequency Transversal Filter With Compact Fiber-Optics And Digital Microelectromechanical System-Based Optical Spectral Control

To the best of our knowledge, for the first time a programmable broadband rf transversal filter is proposed that operates on the principle of broadband optical spectral control implemented with a spatial light modulator input rf signal time delay and weight selection over a near-continuous signal space. Specifically, the filter uses a chirped fiber Bragg grating in combination with a two-dimensional digital micromirror device to enable a programmable rf filter. As a first step, a two-tap rf notch filter is demonstrated with a tuning range of 0.563-6.032 GHz with a 25-dB notch depth at test notch frequencies of 845 and 905 MHz. The proposed filter can find applications in diverse fields such as radar, communications, medicine, and test and measurement. © 2004 Optical Society of America