Frequency-modulated zone plate for coherent noise reduction.

Laser images and holographic reconstructions are highly affected by dust and imperfections present in various optical components of the imaging system, which create noiselike structures in the final images. To reduce this speckle noise, a phase plate based on a frequency-modulated zone plate is proposed. It can be fabricated by holographic techniques, and it does not require a separate Fourier transforming lens. Experimental results are presented showing the capabilities of the phase plate.