Enhancement of Amplified Spontaneous Emission and Laser Performance of Rhodamine 6G/Cellulose Acetate DFB and DBR Waveguide Devices: A Role of Thermally Annealed P(VDF-TrFE) Intermediate Layer

Abstract

Inserting a crystalline P­(VDF-TrFE) intermediate layer under rhodamine 6G (R6G) laser active waveguide layer preserved the emissive R6G molecules in the matrix, which increases the intensity of fluorescence of R6G dye in the matrix and thus enhances the laser performance, including the optical gain of amplified spontaneous emission (ASE). The thermal annealing of the intermediate layer of P­(VDF-TrFE) affects the optical gain of ASE and the laser performance in terms of slope efficiency and the threshold for the R6G/CA waveguide laser devices with DFB and DBR structures. With a higher annealing temperature, the crystallinity, crystallite size, and thus surface roughness of the P­(VDF-TrFE) layer were increased; simultaneously, the fluorescence intensity, the optical gain of ASE, and the slope efficiency were increased, and the threshold for lasing was reduced. Thermal annealing of P­(VDF-TrFE) at 120 °C gave a higher crystallinity, larger crystallite size, and thus deeper surface roughness. A DBR laser device with m = 2 mode number gave a slope efficiency of 4.6% and the optical gain of ASE of 13.0 cm–1. The deeper roughness of the surface due to the larger polar β-crystallites of P­(VDF-TrFE) was significantly related to the increased intensity of fluorescence, optical gain of ASE, and slope efficiency for laser emission and the reduced threshold for lasing. The present approach is the easier way to enhance the lasing performances for ionic laser dyes in industrial applications.

Interfacial Effects of the Photophysics of Rhodamine 6G Ultra-Thin Films on a Poly(methylmethacrylate) Surface

“…Although the surface waves are shallow (a few tens of nm), this may be sufficient to prevent Rh6G transition moments from aligning to form H- or J-dimers. This also may be related to the enhanced lasing behavior seen with Rh6G/cellulose acetate waveguides. , …”

“…This also may be related to the enhanced lasing behavior seen with Rh6G/cellulose acetate waveguides. 28,29 The substrate influences the photophysical properties of Rh6G, as shown in Table 1. The most notable difference in the three substrates is the surface roughness, although there also must be a difference in the surface polarity.…”

“…20−27 It has also been shown that rhodamine 6G (Rh6G) dissolved in a thin layer of cellulose acetate used in a waveguide can enhance laser performance in all solid-state devices. 28,29 In our earlier work, we reported that different rhodamine fluorophores dissolved in dimethylformamide had modulated emission responses after exposure to small quantity of explosive analytes. We selected xanthene dyes as the fluorophore for their low cost, high quantum yield, and long-wavelength absorption and emissions.…”

“…The study of the photophysics of rhodamine dyes has long been of interest because they have large quantum yields, are chemically stable, and can be synthetically modified to absorb and emit light across the entire visible spectrum. Most of the earlier work has been reported on rhodamine dyes dissolved in solution. − However, recently there has been increased interest in the electronic properties of rhodamine and other xanthene thin-film dyes at interfaces. − The rhodamine dyes have also been identified as excellent molecular probes for sensors. − It has also been shown that rhodamine 6G (Rh6G) dissolved in a thin layer of cellulose acetate used in a waveguide can enhance laser performance in all solid-state devices. , …”