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Photothermal technology:
commom-path (single beam) interferometry
- ultimate sensitivity
- Gouy phase shift + Rayleigh range = PCI technology
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About Stanford Photo-Thermal Solutions

Stanford Photo-Thermal Solutions (SPTS) was founded in November 2002. The Photo-thermal Common-path Interferometer (PCI) technology is in the focus of our current activity. The technology was developed in 1997-2000 in the Ginzton Lab, Stanford University.

Our first apparatus was designed in 1998. PCI belongs to a class of pump/probe thermal lens instruments. The focused beam of a pump laser creates local thermal effect, the optical probe experiences phase distortion in the heated area. The original motivation for the instrument was to study induced absorption effects and optical damage in nonlinear optical crystals. With time simpler applications like absorption measurements in coatings, glass substrates became most popular. SPTS offers measurement services and PCI instruments like PCI-03.

The transparent, simple theory of PCI was the key to its success. It was shown that an improved thermal lens configuration could work as a common-path interferometer. Gouy phase shift at the Rayleigh length is behind the interfeometric sensitivity of a single probe beam setup. The concept has been successfully used for evaluation of various optical effects:
Model 02 with two pump ports.
  • Low absorption in the bulk optical materials for high power applications such as sapphire, YAG, fused silica, LiNbO3, KTP, TeO2, etc.;
  • Green light-induced IR absorption in lithium niobate/tantalate family of crystals including periodically-poled crystals;
  • Gray track kinetics and gray track shape in KTP family of crystals;
  • Absorption losses in multilayered HR dielectric mirrors and AR coatings deposited onto fused silica, TeO2 and sapphire substrates;
  • Surface defects and surface contamination of substrates: fused silica, sapphire, LiNbO3, KTP and TeO2.

PPSLT tested at 532 nm
through the edge.

Coating tested at 532 nm.
First custom-built PCI instrument was shipped by the end of the year 2003. During the next year our model PCI-02 and a more compact version configured with an input port for one pump, our model PCI-03 were shipped to major laser companies in the USA, as well as to Israel, China and France.
Model 03 with one pump port.
Stanford Photo-Thermal Solutions

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