Studies On Absorption Length Of Modulation Transfer Spectrum And Its Application In Laser Frequency Stabilization

In this work, optimal absorption length of modulation transfer spectrum has been studied from theoretical analysis and experimental comparisons.Signal to noise ratio(S/N) and slope of modulation transfer spectrum are related to absorption length. An equation of modulation transfer spectroscopy is derived by dividing absorption length into small parts and integrating signal of every unit. Theoretically the relative signal intensity and central slope of spectrum with different absorption length are calculated according to the equation, from which optimal absorption length is obtained and can be used as a reference for experimental application.In experiments, the hyperfine spectra of I₂ at the 532 nm region have been measured by using a diode laser pumped solid state Nd:YAG laser as the light source and taking advantage of the modulation transfer spectroscopy and multi-pass cell. The optical frequency of the laser is locked to the R(56)32-0, a10 hyperfine structure of I₂. Finally both signal to noise ratio and central slope of modulation transfer spectrum of I₂ with different absorption length are compared experimentally and laser frequency stabilities are estimated respectively. The signal to noise ratio (S/N) and central slope are obviously changed with different absorption length, showing that optimal absorption length will contribute to higher laser frequency stability.