Optical amplification of the detection laser light seems an elegant method to improve the sensitivity of a system for the optical detection of ultrasound. However, the amplified spontaneous emission associated to the optical amplification process is a source of both phase and intensity noises. Two configurations are possible, one with the amplifier located ahead of the inspected surface (pre‐amplification) and one after (post‐amplification). We discuss the advantages and drawbacks of these two schemes when a photorefractive two‐wave mixing demodulator is used. © 2004 American Institute of Physics