Measurement and characterization of the frequency noise of a laser-diode-pumped single-frequency Tm-Ho : YAG laser

The frequency noise characteristics of a single-frequency 2.1-mu m Tm-Ho:YA G laser have been thoroughly investigated. From the measurement of the freq uency noise spectral density, performed by means of an interferometric tech nique, a short-term laser linewidth of 550 kHz over 1-ms time interval has been obtained. The frequency stability, defined as the two sample standard deviation of the frequency fluctuations with dead time T, has been also eva luated, obtaining values ranging from similar to 250 kHz to similar to 2.5 MHz for T values between 1 and 100 ms over an observation time of 100 ns. I t has been shown through a numerical analysis that a significant improvemen t is achievable, attaining a frequency stability of similar to 25 kHz for T up to 100 ms, by using the Pound-Drever locking technique in connection wi th a roto-vibrational line of the HBr molecule.