Authors:
Mitsunori Saito
and
Takuya Hashimoto
Affiliation:
Ryukoku University, Japan
Keyword(s):
Droplet Laser, Stimulated Emission, Whispering Gallery Mode, Fluorescence, Silicone Rubber.
Related
Ontology
Subjects/Areas/Topics:
Lasers
;
Photonics, Optics and Laser Technology
;
Quantum Electronics and Laser Science
Abstract:
A cylindrical droplet laser was fabricated in a silicone rubber by using a polyethylene-glycol solution of
rhodamine 6G. The silicone rubber provided a simple molding process for enclosing the droplet, since
silicone oil solidified at room temperature by only adding a curing agent. Polyethylene glycol dissolved a
large amount of dye molecules, yielding a fluorescent solution whose refractive index (1.46) was higher
than that of the silicone rubber (1.40). Consequently, some fluorescence rays circulated in the cylindrical
droplet owing to the total internal reflection on the side surface (the whispering gallery mode). Other
fluorescence rays made round trips in the radial or axial directions of the cylindrical droplet (the radial and
axial modes) being reflected at the side or bottom surfaces. When the droplet was excited by a green laser
pulse (wavelength: 527 nm, pulse duration: 10 ns), these emission modes competed with one another to
induce a stimulated emission. In a droplet with
2.0 mm diameter and 1.4 mm height, the whispering gallery
mode conquered the other emission modes, exhibiting a non-linear peak growth and a peak-width narrowing
when the excitation energy exceeded 20 μJ (the threshold energy of the stimulated emission).
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