Abstract

Femtosecond pump-probe spectroscopy is a well-known method used to investigate ultrafast excited state dynamics in condensed matter, chemical, and biological systems. The standard technique uses a narrowband pump and continuum probe to excite the sample, and employs a spectrometer to acquire the wavelength dependent absorption saturation dynamics. This technique often requires the use of a femtosecond amplifier to achieve sufficient intensities for continuum generation and sufficient pump-probe signal magnitudes. With the development of 5 fs lasers, which can generate spectra spanning one octave, spectrally resolved pump-probe measurements can be performed without the need for amplifiers [1,2,3]. Although the pulse repetition rate from a laser oscillator is extremely high, pulse energies are low and signal levels are small. Standard CCD detectors cannot detect modulated signals and thus it is not possible to take advantage of high signal to noise measurements that are possible with high repetition rate laser sources. Here, we present a new technique that enables the parallel acquisition of pump-probe measurements for multiple wavelengths. This is made possible using a novel, two-dimensional smart pixel detector array, which was originally developed for high speed optical coherence tomography (OCT) [4,5]. Each pixel performs amplitude demodulation, and in combination with a diffraction grating, probe transmission signals can be acquired in parallel for multiple wavelengths. The smart pixel array can achieve sensitivities comparable to lock-in amplification but can perform demodulation of probe transmission signals at multiple wavelengths simultaneously, enabling time and wavelength resolved femtosecond pump-probe spectroscopy.

© 2002 Optical Society of America