Abstract: A new method is presented for measuring the laser wavelength. The experimental results are compared with those obtained by the classical Michelson interferometry. We analyze the diffraction spectra of the ultrasonic grating formed by mercury and He-Ne lasers through ethanol solution （97%）. We study further the effect of temperature on the velocity of ultrasonic wave propagation that is first measured using mercury laser. The wavelength of He-Ne laser can be accordingly calculated from the velocity of ultrasonic wave propagation. The relative error between the calculated and the standard values is 0.55%. The new method is comparable to the classical Michelson interferometry.

Key words: ultrasonic diffraction grating, ultrasonic velocity, He-Ne laser