Transient Molecular Spectroscopy with a Frequency-Doubled Diode Laser

A tunable cw low-amplitude noise laser is useful in the measurement of reaction rate constants of short-lived molecules. We are using an injection-locked diode laser together with a potassium niobate (KNbO3) crystal in a build-up cavity to generate tunable blue light. The blue light is then used to measure absorption due to iodine-monoxide (IO). This molecule is believed to play a role in the atmospheric ozone cycle.1 Chemical reactions involving IO are studied by monitoring transmittance through a flow cell in the wavelength range near 427 nm. IO is produced in the cell by photolysis of I2 and ozone with an excimer laser pulse; subsequent decay of the IO concentration takes place in approximately 10 ms. To accurately measure these fast reaction rates in low concentrations, optical absorptions of less than 10-4 are monitored with a 40 kHz bandwidth. Amplitude stabilization of the doubled light is necessary and is implimented with an electro-optic modulator.