Advanced LIGO subsystems
are the organizational units of the overall project. Follow the links below to view the mission and progress of each subsystem.

Auxiliary Optics Core Optics
Data Acquisition Data and
Input Optics

LIGO Technology Development and Migration

Explore the menu of case study links (left) to view impacts of LIGO technology across the broader science and engineering community.

Technology Type:  High Performance Optics and Optical Metrology

Photo-Thermal Common-Path Interferometry

** Institution:  Stanford University
** Contact:  Alexander Alexandrovski  

      Stanford Photo-Thermal Solutions
      15-1598 6th Avenue, PO Box 493039, Keaau, HI 96749  408.898.0446

** Supporting Agency:  National Science Foundation
** Technology Source:  LIGO Scientific Collaboration (LSC) members
      outside of LIGO Laboratory

[ptcpi]The commercial use of nonlinear optical materials requires that properties other than nonlinear coefficients and birefringence be measured. These properties include absorption, surface and bulk damage limits, grey tracking and green induced infrared absorption. One of the most important properties is simple light absorption. In the early years of the field the absorption was large but as the materials improved and the absorption became smaller, more sensitive measurement techniques were needed. When Advanced LIGO began development in the late 90s, [ptcpi]it was clear that a close comparison between the properties of silica and sapphire for test mass substrates would require measurements techniques with much higher sensitivity. The absorption of the ion beam sputtered coatings in aLIGO would be in the sub-ppm region. Several different pump probe techniques were developed, but the best approach was the Photo-Thermal Common Path Interferometry (PTCPI) developed at Stanford University by Alexander Alexanderovski.

[ptcpi]In PTCPI a small high-power pump laser beam is used to illuminate a sample to be measured, and a second larger low-power probe is centered on the first beam. The thermo-optic distortions due to the heating of the sample by the pump beam produce a small lens-like distortion on the probe beam phase front and CTCPI measures this distortion with dual-beam interferometric sensitivity. In response to a broad interest in this approach, a company was incorporated, Stanford Photo-Thermal Solutions, (SPTS) to meet the needs of the optics community for industrial and research equipment for the measurement of surface and bulk absorptions, and also to provide services for the measurement of samples. Since its founding SPTS has had sold 30 complete measurement systems and has over 100 service customers in the optics and homeland security communities and is currently incorporated and operating in Hawaii.

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