Cylindrical microcavity laser based on the evanescent-wave-coupled gain.

Area of Science:

• Optics and Photonics
• Laser Physics
• Materials Science

Background:

• Whispering gallery mode (WGM) resonators are sensitive to external perturbations.
• Evanescent field coupling offers a pathway for non-invasive interaction with WGM resonators.
• Achieving laser oscillation in microcavities often requires precise gain medium integration.

Purpose of the Study:

• To demonstrate a novel microcavity laser design utilizing evanescent field gain.
• To investigate laser oscillation in a cylindrical microcavity coupled to an external gain medium.
• To characterize the performance of such a laser, including mode selectivity and quality factor.

Main Methods:

• Fabrication of a cylindrical microcavity (125 microm diameter).
• Surrounding the microcavity with Rhodamine 6G dye in ethanol (lower refractive index).
• Excitation of the dye molecules via the evanescent field using a second harmonic Nd:YAG laser.

Main Results:

• Successful laser oscillation of whispering gallery modes was observed.
• Single-mode laser oscillation at approximately 600 nm, corresponding to a transverse magnetic (TM) mode, was achieved.
• A high cavity quality factor (Q) of 3x10^7 was measured.

Conclusions:

• Evanescent field gain is a viable mechanism for microcavity laser operation.
• This approach enables single-mode laser oscillation with high Q factors.
• The demonstrated microcavity laser offers potential for applications requiring narrow linewidth and high sensitivity.