Thermal Lens Spectrometer Yields High Sensitivity

Thermal lens spectrometry is a highly sensitive method for detecting very small quantities of material by the absorption of light from a laser source. It takes advantage of the thermal lens effect to measure the absorption spectrum of a sample. This invention utilizes an optical parametric oscillator (OPO) to obtain a continuously tunable laser source over a wide spectral range. A pump beam from the OPO and a probe beam from a laser are directed coaxially through a flow cell containing a sample. Sensors measure the intensity of the light from the probe beam after it has passed through the sample, while the OPO is tuned through a range of frequencies. Changes in the probe beam intensity measurement result from the wavelength-dependent heating of the sample by absorption of the pump beam. A plot of these intensity changes therefore provides a characteristic signature of the substance in the flow cell.