Ultra-low Threshold Titanium doped sapphire Whispering-gallery Laser

TL;DR

This paper demonstrates the first Ti:sapphire whispering-gallery laser with ultra-low threshold and high efficiency, utilizing a novel gain evaluation method and opening new possibilities for compact Ti:sapphire laser applications.

Contribution

It introduces the first Ti:sapphire whispering-gallery laser with a low threshold and high Q, along with a new gain measurement technique in the near infrared.

Findings

Lasing threshold reduced to 14.2 mW

Laser slope efficiency increased to 34%

Novel gain evaluation method demonstrated

Abstract

Titanium doped sapphire (Ti:sapphire) is a laser gain material with broad gain bandwidth benefiting from the material stability of sapphire. These favorable characteristics of Ti:sapphire have given rise to femtosecond lasers and optical frequency combs. Shaping a single Ti:sapphire crystal into a millimeter sized high quality whispering gallery mode resonator ($Q\sim10^8$) reduces the lasing threshold to 14.2 mW and increases the laser slope efficiency to 34%. The observed lasing can be both multi-mode and single-mode. This is the first demonstration of a Ti:sapphire whispering-gallery laser. Furthermore, a novel method of evaluating the gain in Ti:sapphire in the near infrared region is demonstrated by introducing a probe laser with a central wavelength of 795 nm. This method results in decreasing linewidth of the modes excited with the probe laser, consequently increasing their $Q$. These findings open avenues for the usage of whispering gallery mode resonators as cavities for the implementation of compact Ti:sapphire lasers. Moreover, Ti:sapphire can also be utilized as an amplifier inside its gain bandwidth by implementing a pump-probe configuration.