Autocollimator for spectroscopy of broad resonances with pulsed lasers.

For the application of autocollimation spectroscopy [Z. Phys. D 18, 249-255 (1991)] a pulsed dye laser that is emerging from a focus (diameter, 1 mm; divergence, 30 mrad) has to be reflected back in itself with high precision. The difference Δθ between the mean angles of the counterpropagating laser beams has to be less than 1 × 10(-6) rad. Using a paraxial approximation, we show that a cat's eye fulfills the needs best. An adjustment procedure together with additional calibration equipment (CCD arrays and quadrant diodes) for the device is presented. Accounting for the uncertainties of the adjustment and using ray tracing, we show that Δθ ≤ 5 × 10(-7) rad can be achieved.