Laser-raster spectrometer for time-resolved recording of transient absorption

For measurements of transient absorption a laser-raster technique has been found to be surprisingly sensitive. It utilizes spatial separation of excit ation and probing by employing a fast-flowing jet stream. The time resoluti on is determined by the flow velocity and the focal diameters of the contin uous excitation and probing laser beams. Changes in transmission can be det ected in the spectral region from 350 to 1000 nm. A dual-frequency modulati on technique is used to achieve a sensitivity of 10(-4). The time resolutio n is 0.5 mu s. The performance of this spectrometer is demonstrated by meas urement of the absorption of the transient states of Rhodamine 6G dye in et hylene glycol. (C) 1999 Optical Society of America OCIS codes: 300.6500, 30 0.6550, 300.6360, 300.6390, 300.6190.