Absorption of Low-Loss Optical Materials Measured at 1064 nm by a Position-Modulated Collinear Photothermal Detection Technique

A collinear photothermal detection bench is described that makes use of a position-modulated heating source instead of the classic power-modulated source. This new modulation scheme increases by almost a factor 2 the sensitivity of a standard mirage bench. This bench is then used to measure the absorption coefficient of OH-free synthetic fused silica at 1064 nm in the parts per 106 range, which, combined with spectrophotometric measurements, confirms that the dominant absorption source is the OH content. [Optical Society of America ]