Polarization features of optically pumped CdS nanowire lasers

TL;DR

This study investigates how the polarization of optical pumping affects the efficiency and polarization characteristics of CdS nanowire lasers, revealing enhanced absorption and polarization dynamics during lasing.

Contribution

It demonstrates the polarization dependence of pump absorption and the polarization properties of nanowire lasing emission, highlighting the role of pump polarization in nanowire laser operation.

Findings

Maximum pump efficiency occurs with polarization parallel to nanowire axis.

Degree of polarization of emission increases from 15% to 85% during lasing.

Emission polarization is independent of excitation polarization.

Abstract

High quality CdS nanowires suspended in air were optically pumped both below and above the lasing threshold. The polarization of the pump laser was varied while emission out of the end facet of the nanowire was monitored in a 'head-on' measurement geometry. Highest pump-efficiency and most efficient absorption of the pump radiation are demonstrated for an incident electric field being polarized parallel to the nanowire axis. This polarization dependence, which was observed both above the lasing threshold and in the regime of amplified spontaneous emission, is caused by an enhanced absorption for parallel polarized optical pumping. Measured Stokes parameters of the nanowire emission reveal that due to the onset of lasing the degree of polarization rapidly increases from approximately 15% to 85%. Both, Stokes parameters and degree of polarization of the nanowire lasing emission are independent of the excitation polarization. The transversal lasing mode is therefore not notably affected by the polarization of the pumping beam, although the supply with optical gain is significantly enhanced for an excitation polarization parallel to the nanowire axis.