Helium‐neon laser beam deflection is used to study excimer laser ablation of polymers and a YBa2Cu3O7−xsuperconductor. Density gradients above pulsed laser heated or ablated samples deflect the He‐Ne laser beam and this is measured using a position sensitive detector. The technique permits the determination of the laser fluence threshold for ablation both in a vacuum and in air, and the velocity of the ablation products in a vacuum. A model of the thermal deflection at low fluence was developed which enables measurements of thermal diffusivity of the air.