Abstract

The amplitude stability of laser sources is of great interest to improve detection sensitivity in many applications as metrology, sensors, and optical communications [1]. In this work we experimentally investigate the amplitude noise characteristics of the Tm:Ho laser system and we demonstrate reduction of the intensity noise and complete suppression of the relaxation oscillation peak of a diode-pumped single-frequency Tm-Ho:YAG laser. Intensity noise suppression is achieved by means of a suitable electronic feedback circuit acting on the drive current of the pump diode. The length of the end-pumped plano-convex Tm-Ho:YAG laser cavity is ~55 mm. A 150-µm thick intracavity etalon (R~80%) provides for single-frequency operation and tuning around the 2097-nm wavelength The laser generates an output power of ~35 mW at 620 mW pump power (λ~780 nm). Theory and experiments show that in the Tm-Ho laser the main source of intensity noise is due to pump power fluctuations. To properly design the feedback circuit we first experimentally characterized the effect of pump power fluctuations on the relative intensity noise (RIN) of the Tm-Ho laser. This phenomenon is rather complex because Ho³⁺ ions are indirectly excited by means of Tm³⁺ ions trough an energy-transfer (ET) process, which acts as an intermediate step in the pumping process [2].

© 2000 IEEE