Single-mode laser operation of CdSe/CdS Core/Shell colloidal quantum rods on silica microspheres

Grivas, C., Andreakou, P., Wang, Pengfei, Ding, Ming, Brambilla, G., Manna, L. and Lagoudakis, P.G. (2012) Single-mode laser operation of CdSe/CdS Core/Shell colloidal quantum rods on silica microspheres. E-MRS '12 Materials Research Society Spring Meeting, Strasbourg, France. 14 - 18 May 2012.

Abstract

Single-mode operation of fiber-coupled hybrid lasers based on colloidal CdSe/CdS core/shell nanorods in silica microspheres is reported. The spheres were pumped at a wavelength around 400 nm with a tunable frequency doubled Ti:sapphire amplifier, operating at 250 KHz and emitting 180 fs-short pulses with a linewidth of 5 nm. Pump pulses were evanescently coupled into the spheres with adiabatic tapers made of single-moded fibers at 405 nm. Laser signals were collected by either a fiber tip with a diameter of ~50 nm or, the same taper used for pumping. To optimize pump efficiencies, phase-matching of the propagation coefficients between the propagating mode in the taper and the fundamental whispering-gallery-mode (WGM) in the microsphere was established.
Single-WGM operation at ~628 nm, corresponding to the 1Sh-1Se(CdSe) transition of a microsphere with a 9.2 µm diameter was obtained by resonant pumping a fundamental WG pump mode at the equatorial ring of the sphere with |m| = l, where m and l are the angular momentum and the azimuthal numbers, above an absorbed pump power threshold of 67.5 µW. Microspheres with larger diameters produced multimode laser emission. A maximum output power of 5.5 µW for 155 µW of absorbed power was measured, corresponding to a slope efficiency of 6.4%.
Wavelength tunability over a range of 2.1 nm (which corresponds to 30% of the FSR) was achieved for the lasing wavelength, by heating with 3.5 µm-pulses of 200 fs duration and 80 MHz repetition rate.

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Contributors

Author: G. Brambilla

Author: P.G. Lagoudakis

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