Electrically Tunable Laser-Induced Voltage of Coffee

In this work, the laser-induced voltage (LIV) of a selected commercial coffee was studied. We focused on the electrically tunable LIV response under a krypton fluoride (KrF) pulsed laser irradiation. The typical LIV transient consisted of three components of fast rise within 40 ns, slower rise from 0.04 to 100 mu s, and attenuation after 100 mu s. The response process was fit by the sum of the three exponential functions, which was in agreement with the measured LIV data. The time dependences of LIV were tuned strongly by bias voltage and laser energy. Higher laser energy and bias voltage enhanced LIV, in contrast the rise time and full-width at half-maximum (FWHM), were negatively correlated with laser energy and bias voltage. The LIV decay time was shortened significantly by reducing the adjustable resister parallel to the coffee sample. When an impendence of 10 Omega was applied, the LIV trace was almost triangular and symmetrical, and the response time was completely limited by the laser pulse duration. Furthermore, the LIV response increases with laser energy.