The manufacturing process uses a semiconductor-like laser pointer process in which cadmium sulfide (CdS) nanowires (refractive index n = 2.67) are grown on a silicon wafer substrate using chemical vapor transport. After that, the nanowires were directly deposited on the silicon glass cover, and then exposed to low pressure plasma. This plasma treatment is used to ensure that the nanowires are fixed on the glass surface, which is used for experiments in a liquid environment.
In the experiment, the nanowires were immersed in a mixed solution of ethanol and toluene in a volume ratio of 10: 0, 9: 1, 8: 2, and 7: 3, corresponding to refractive indexes of 1.365, 1.39, 1.339, and 1.407, respectively. The nanowire was excited by a pulsed optical parametric oscillator (5 nanosecond pulse width, 20 Hz repetition frequency, 479 nm wavelength). Then use a 50 × objective lens with a focal size of 60 μm to focus the pump beam. Figure 2 shows the resulting laser spectrum for each refractive index, all using the same excitation energy density of 4 μJ / mm 2.
Refractive index sensing based on semiconductor nanowire green laser pointer. The test results also show that the wavelength effect is also very sensitive. For example, when the refractive index is increased from 1.365 to 1.407, a clearly measurable red shift phenomenon from 504.35 nm to 505.23 nm occurs.
Further analysis of the data based on the 0.22nm linewidth of the laser peak and other factors shows that the overall quality factor (FOM) of the design is 96. The semiconductor nanowire sensor is not only a 24-fold improvement in the results achieved using the resonance scattering method, but also its manufacturing complexity is low. It can be internalized into living cells and sense the refractive index of each part.