A distributed-feedback grating excited by a CW laser diode for portable detection of explosive vapors with high sensitivity and stability

The practicality of non-contact detection of explosive vapors has always faced challenges in miniaturization, sensitivity, and stability. A distributed-feedback (DFB) grating coated with a widely available polyfluorene film has been reported to show improved sensitivity but by the use of high-power pulses from large volume equipment. Here, our study introduces a promising portable design of a DFB sensor that can be pumped by a continuous wave (CW) laser diode to achieve the resonant enhancement effect of fluorescence, and the pump power can be as low as a few milliwatts but still high sensitivity and stability for trace explosive vapor detection can be generated. Moreover, both COMSOL simulations and experiments were conducted to study the influence of the sensor structure on the resonant enhancement and sensing performance. The results evidence that the explosive vapor quenching efficiency of the DFB grating sensor is obviously affected by the grating groove depth and the polyfluorene film thickness, and the highest quenching efficiency can reach 98.3% at 60 s when the average thickness of the polyfluorene film is 20 nm and the grating groove depth is 200 nm. The sensitivity and stability of DFB grating sensors were greatly improved compared with those of the conventional planar substrate sensors, and the signal-to-noise ratio of detection was improved by one order of magnitude. The reusable corrosion-resistant quartz grating, longer luminescence lifetime and low pump-power laser diode will greatly cut the cost of the DFB grating sensor, improve the integration of a detector, and make its application in portable chemical sensor products possible. The practicality of non-contact detection of explosive vapors has always faced challenges in miniaturization, sensitivity, and stability.