Author Affiliations
1School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China2School of Science, Qingdao University of Technology, Qingdao 266520, China3Faculty of Electronic Information Engineering, Huaiyin Institute of Technology, Huaian 223003, Chinashow less
Fig. 1. (a) Diagram of the experimental setup; (b) comparison between photoluminescence (PL) spectrum excited by a continuous wave laser at 20 mW/cm2 and the amplified spontaneous emission (ASE) excited by a 10 ns pulsed laser at 96.5 μJ/pulse of 5 mg/mL ethanol solution of rhodamine 6G (Rh6G). Inset is the molecular structure of Rh6G.
Fig. 2. (a) Emission spectra of a 5 mg/mL Rh6G ethanol solution with a fiber at various excitation intensities. Left inset: sample configuration; the bare fiber rests on the cuvette wall vertically by capillary force. Right inset: emission spectrum excited at 3.7 μJ/pulse. TE, transverse electric; TM, transverse magnetic. (b) Integrated intensity of the emission as a function of excitation pulse energy, indicating a threshold behavior.
Fig. 3. Single-mode emission from various samples and from various excitation positions in the same sample, all excited using similar pulse energy (∼10 μJ/pulse). S1 (2, 3): sample 1 (2, 3). S1. P1(2, 3): position 1 (2, 3) in sample 1.
Fig. 4. (a) Scheme of a fiber with coating layer at one end in the 5 mg/mL Rh6G ethanol solution. Two positions on the fiber are marked as 1, 2, respectively; (b) corresponding spectrum excited at two positions by a nanosecond (ns) pulsed laser at pump energy of ∼8 μJ/pulse.
Fig. 5. (a) WGM spectra at various excitation intensities from a fiber in a 5 mg/mL Rh6G ethanol solution. Sample configuration was schematically shown in the left inset, with a bare fiber being coated with PMMA (∼thickness of 1 μm) at both ends. Right inset: typical emission spectrum of one WGM mode with FWHM of 0.1 nm; (b) integrated intensity of the emission as a function of excitation pulse energy, indicating a threshold behavior.
Fig. 6. WGM spectra of a fiber in 5 mg/mL Rh6G solution of mixed ethanol and ethylene glycol with different ratios. The pump energy is ∼10 μJ/pulse; in this configuration, the fiber sticks to the cuvette wall. The corresponding refractive indexes are marked at each spectrum. The single-mode emission spectra, which are circled, are also zoomed to show the lack of spectral shift (left inset). Right inset is the WGM emission from a bare fiber in MEH-PPV/THF solution using the same configuration.
Fig. 7. Plot of
γ(λ), which is the fraction of the excited molecules at the laser threshold for various
Qsolution=ηQ;
Q is the quality factor of the cavity, and
η is the occupation factor, which is defined as the fraction of the evanescent field volume to that of the whole WGM [
27].
Fig. 8. Emission spectra from a fiber in 5 mg/mL rhodamine B ethanol solution at various excitation intensities with the same sample configuration as in Fig. 2(a). Left inset: PL spectrum of the solution excited at 20 mW/cm2; right inset: molecular structure of rhodamine B.