The accurate frequencies of the methane molecular transitions have been widely used in laser stabilization. The frequency of the 3.39-μm He-Ne laser stabilized by methane lines was measured using several methods; as a result, an optical frequency standard was designed.
The laser-saturated absorption lines of methane at 2.36 μm have been shown to have remarkable characteristics for the frequency stabilization of a Cr:ZnSe laser. A two-mode method of nonlinear saturation spectroscopy was applied for obtaining an important spectroscopic information about the E(2) line of the methane vibrational-rotational ν1 + ν4 band for further laser frequency stabilization.
Optical frequency combs based on different femtosecond lasers were proposed for the generation of low-noise microwaves. Er-doped all-fiber hybrid mode-locked ring laser was demonstrated for the further development of stabilized combs. The idea of solid-state femtosecond mid-IR lasers on Cr:CdSe, Cr:ZnSe, Fe:ZnSe crystals was discussed. New method for the purpose of improving the active media transmission based on effective media theory was proposed.
Several methods of stable optical frequency transfer to microwave region were discussed.
Transportable ultrashort-pulse lasers stabilized by using optical frequency standards constitute an important tool in the emerging field of optical frequency metrology and are enabling unprecedented measurement capabilities and new applications in a wide range of fields, including precision spectroscopy, atomic clocks, ultracold gases, and molecular fingerprinting.