  The development of a multiple-channel lock-in optical spectrometer (LIOS) is
presented, which enables parallel phase-sensitive detection at the output of an
optical spectrometer. The light intensity from a spectrally broad source is
modulated at the reference frequency, and focused into a high-resolution
imaging spectrometer. The height at which the light enters the spectrometer is
controlled by an acousto-optic deflector, and the height information is
preserved at the output focal plane. A two-dimensional InGaAs focal plane array
collects light that has been dispersed in wavelength along the horizontal
direction, and in time along the vertical direction. The data is demodulated
using a high performance computer-based digital signal processor. This parallel
approach greatly enhances (by more than 100x) the speed at which spectrally
resolved lock-in data can be acquired. The noise performance of a working
system optimized for the 1300 nm wavelength range is analyzed using a laser
diode light source. Time-resolved absorption traces are obtained for InAs
quantum dots embedded in a GaAs matrix, and for dispersed films of PbSe
nanocrystals.
