Selection of Emission Wavelength of Lasing via a Hybrid Microcavity

In the applications of optical communication and light-matter interaction manipulation, the capability of on-demand lasing output with programmable and continuous wavelength tunability over a broad spectral range under low threshold is key functionality. However, the ability to control multiwavelength lasing characteristics within a small mode volume with high reconfigurability remains challenging. The number of dyes and the emission wavelengths of existing materials always restrict the color gamut. In this Letter, we introduce a selection of emission wavelength laser by injecting Rhodamine 6G solution mixed with $\mathrm{Au}$ nanoparticles in the metal-cladded slab-capillary hybrid microcavity. A mechanism for tuning laser emission wavelengths is designed by manipulating the diameter of $\mathrm{Au}$ nanoparticles in Rhodamine 6G solution. Precision control of distinctive lasing wavelengths and a narrower peak are achieved, along with a stable lasing beam output from both ends of the capillary due to coherent superposition. Our findings offer possibilities for realizing a micro selection of emission wavelength laser from a single overall structure.

Figure 1

Structural characterization and experimental system in the metal-cladded slab-capillary hybrid microcavity. (a) Schematic diagram of the hybrid microcavity. (b) Electromagnetic field distribution for the slab-capillary microcavity using comsol software. (c) Injecting R6G solution with $\mathrm{Au}$ nanoparticles by a microinjector into the hollow-core capillary [25]. (d) Reflectance spectra of the modes for the slab-capillary waveguide versus the incident angle. (e) Experimental system and setup, the chip is fixed on the $\theta /2\theta$ synchronous rotator and rotated by a personal computer(PC).

Figure 2

Laser emission in the capillary hybrid microcavity. (a) Fluorescence spectrum of R6G. (b) Injection of $\mathrm{Au}$ nanoparticles and R6G into the capillary under the action of pump light can catch the lasing beam. (c) Approximately 594 nm laser beam after passing through the transmissive narrow-band filter. (d) The laser intensity at approximately 594 nm varies with the pump light at 532 nm. (e) The spectrum of the pumping and laser beam using the spectrograph.

Figure 3

The relationship between input pumping and output lasing. (a) The threshold of lasing. (b) The relationship between intensity of input pumping and output lasing. (c) The intensity of lasing corresponding to the three intensities of the input pumping.

Figure 4

Comparison of laser beams after injecting $\mathrm{Au}$ nanoparticles with different diameters. (a)–(c) The intensity of light from the capillary mixed with $\mathrm{Au}$ nanoparticles of 40, 50, and 60 nm. The black line corresponds to a stronger pump light power (∼10 µW) while the red line corresponds to a pump light power of approximately 5 µW. (d) The intensity of light from the capillary without $\mathrm{Au}$ nanoparticles.

Figure 5

Theory and simulation of the structure. (a)–(c) The scattering efficiency, extinction efficiency, and absorption efficiency of $\mathrm{Au}$ nanospheres with a diameter of 40, 50, and 60 nm in R6G. (d) The resonance wavelength of $\mathrm{Au}$ nanospheres varies with diameter in R6G.