Spectral Narrowing of a Dye Laser Using a Vapor Prism

Abstract

A novel method for narrowing the spectrum of a dye laser is realized by using a vapor prism. In a vapor cell which has a heated boat and a cooler top, the vapor will be found to be very dense along the boat and highly attenuated along the top in presence of foreign gas. Thus a sodium vapor cell behaves as the optical equivalent of a prism with a variation of refractive index along the vertical direction. This vapor prism has a large dispersive power in the anomalous dispersion region near the resonance line.
The dispersion curve of the prism using sodium vapor was measured and the dispersive power at the wavelength of 5891. 5Å is equivalent to that of a diffraction grating with 2×10⁴ grooves per mm. With the vapor prism inside a laser cavity, a laser oscillation spectrum of less than 0.1Å was obtained at sodium temperature of 320°C.