Low Fluence, High Sensitivity Optical Pump/Supercontinuum Probe Spectroscopy

Obtaining spectroscopic information from ultrafast time-resolved measurements either requires discrete scanning of the probe wavelength and repeated measurement, or the use of high fluence laser systems and supercontinuum generation that must be measured with a CCD camera. While this latter approach can yield a wealth of information across a wide swath of photon energies, the required CCD cameras can be expensive while not providing as sensitive measurement as available with lock-in detection. Here, we describe a novel optical pump-supercontinuum probe apparatus based on a nonlinear photonic bandgap fiber and a digital mirror device that allows for lock-in detection of the time resolved change in reflectivity across a spectrum that spans from ~500 - 800 nm with the possibility to reach wavelengths as long as 1600 nm. Notably, our device relies on a single element detector instead of CCD cameras, and since it is based on a Ti:sapphire oscillator system, it can be performed at high repetition rates and and much lower incident fluences as compared with approaches based on amplified lasers.