Strobe captures light and improves velocity measurements

Strobe captures light and improves velocity measurements

Researchers at Purdue University (West Lafayette, IN) have demonstrated a new method for more accurately measuring velocity by using oscillatory mode coupling between two coherent laser beams. The coupling is produced by moving an interface pattern against a quasi-static electrically strobed grating in a photorefractive aluminum gallium arsenide/gallium arsenide multiple-quantum-well diode laser operated in the quantum-confined Stark geometry. The strobe is used to determine velocity by measuring the Doppler shift of laser light reflected off a moving object. According to Michael Melloch, professor of electrical and computer engineering at Purdue, it traditionally has been difficult to get a reliable measurement of the Doppler shift because the light reflected back does not have uniform intensity patterns and is degraded by vibrations, changes in temperature, and atmospheric effects. He says this new method eliminates such nuisance effects by using dynamic holography, in which the semiconductor device acts as a holographic film. When an electrical pulse--the strobe--is applied across the device, it takes a holographic snapshot of the light hitting it. The strobe frequency is in the kilohert¥range and filters out the nuisance frequencies, while the Doppler-shifted light coming from the moving object, with its frequency in the megahert¥range, passes through the device to a detector. Melloch sees applications in manufacturing, remote sensing, and laser ranging.