Abstract

Using a 393 nm Nichia NLHV500 laser diode as a photodetector we present results demonstrating a strong two-photon response across a 200 nm range of visible wavelengths which enables sensitive measurement of intensity and interferometric second-order autocorrelations Results are presented at three wavelengths - 440, 540 and 630 nm - which could be accessed both by CW and modelocked laser sources available to us and the single-photon and two-photon response of the laser diode was found at each of these wavelengths. The modelocked sources were based on a 100 fs Ti:sapphire laser with a repetition rate of 85 MHz which synchronously pumped a PPLN optical parametric oscillator (OPO) with an average signal output power from 1080 - 1260 nm of around 300 mW. By single-pass frequency doubling the OPO output in a 2 mm BBO crystal we were able to produce around 10 mW of red light tunable from 600 - 630 nm and up to 5 mW of green output at 540 nm. Blue light was produced by tuning the Ti:sapphire laser to 880 nm then frequency doubling its output to produce up to 20 mW of average power at 440 nm. We used HeNe, frequency-doubled Nd:YVO₄ and HeCd lasers to produce the CW outputs at 633, 532 and 442 nm used to measure the linear response of the diode. In all the experiments we focused the light into the diode using a standard 20x microscope objective and the generated photocurrent was measured directly (no applied bias) by connecting the diode output across the terminals of a 1MΩ oscilloscope

© 2000 IEEE