Fig. 1. Experimental setup. A potassium titanyl phosphate (KTP) crystal served as a frequency doubling crystal; the cavity mirror had high transmission (HT) at 532 nm ($\mathrm{HT}=90\%$) and high reflectance (HR) in the range of 560 nm to 700 nm ($\mathrm{HR}=90\%$); the output coupler had partial transmission ($R=85\%$) from 400 nm to 700 nm.

Fig. 2. (a) Laser/FL spectrum. (b) Slope efficiency curve and FWHM of the output spectrum. (c) Oscilloscope trace of output laser. (d) Spectra of output laser in 60 μg/mL NR/ethanol solution containing SA in different concentrations. (e) Spectra of output laser in 200 μg/mL NR/ethanol solution containing SA in different concentrations.

Fig. 3. Bathochromic shift of laser wavelength corresponding to different concentrations of doped SA.

Fig. 4. (a) Tandem cuvette detection system of SA. Inset figure: details of tandem cuvette structure containing R6G/ethanol and NR/ethanol with SA. (b) Spectra of output laser in tandem cuvette system with high concentration of SA from 0 ppm to 500 ppm. The laser peak at 565 nm was in the spectrum of R6G/ethanol. (c) Spectra of output laser in tandem cuvette system with low concentration of SA from 1 ppm to 10 ppm. The laser peak at 565 nm was in the spectrum of R6G/ethanol.

Table 1. FL Spectra of Nile Red in Different Solvents

Table 2. Wavelength of Laser Output in 60 μg/mL NR/Ethanol Solution Corresponding to Different SA Concentrations

Table 3. Wavelength of Laser Output in 200 μg/mL NR/Ethanol Solution Corresponding to Different SA Concentrations

Table 4. Intensity Ratio of Dual-wavelength Laser and Wavelength Position Corresponding to Different Concentration of SA in Tandem Cuvette System