Spectroscopy Works with Single Pulse

Physicists at Weizmann Institute of Science in Rehovot, Israel, have demonstrated that a single tailored laser pulse can replace the two or three typically required in coherent anti-Stokes Raman spectroscopy and microscopy. Described in the Aug. 1 issue of Nature, the technique promises to simplify the apparatus for these applications, especially for nonlinear microscopy.

The scientists employed a computer-controlled spatial light modulator to shape the spectral phase of the 20-fs pulses from a Ti:sapphire laser, enabling a pulse to selectively excite a particular vibrational level in the sample and to suppress the background noise. The returning signal displays resonant oscillations in samples that have one Raman level in the measured range or beating in samples that have more than one.

To illustrate the application of the technique, the researchers imaged CH₂Br₂ in 10-µm-diameter wells in a glass capillary plate.