Photochromic film profiles UV pulses

The single-shot beam profiles of a series of 20-ns pulses from a frequency-tripled Nd:YAG laser show bimodality induced by deterioration of the nonlinear crystal. The images were captured by the UVSC-365 SensorCard (SensorPhysics, Oldsmar, FL), a photochromic film that is responsive to exposure at wavelengths from 0.8 to 500 nm. To obtain the images, the card was passed through the beam; the resultant pattern was digitized for quantitative analysis by a separate system.

The film produces images almost instantly, without any developing process. The rapid response of the film to the wavelengths of interest captures pulse-to-pulse variations that would otherwise be averaged out in measurements involving tens or hundreds of shots. Sensitivity to fluorescent and incandescent illumination falls off rapidly, so ambient light has negligible effect during the measurement and digitization process. Image color varies as a function of incident intensity (see scale at left of figure); images can be calibrated for absolute fluence so that analysis yields integrated intensity and energy distribution for each shot. The method can also determine beam diameter and x and y profiles.

The cards offer spatial resolution of better than than 1 µm. Uses include characterization of ultraviolet laser beams for micromachining applications.