Knowledge Bank

We have developed a new data acqisition system for diode laser spectrometers used to measure spectra of transient molecules formed photolytically using a pulsed laser. The new system employs a novel segmented refective chopper wheel whose rotation is synchronized to the photolysis laser firing. The wheel splits the time between photolysis laser shots into four slices and three spatially scparate beams which measure (i) the transient sample of interest (ii) a reference gas spectrum and (iii) an \’{e}talon spectrum. The three beams are recombined on the element of a single detector, amplified and passed to a CAMAC programmable transient recorder controlled by a PC. We are able to measure the sample, reference and \’{e}talon spectra and the $I0$ level on every laser shot thereby improving both the speed and accuracy of the mesurements. We illustrate the results by reference to new spectra of the HOCO and ethyl radicals.