Optical absorption measurements with parametric down-converted photons.
It has been known for some time that correlated detection of pairs of photons generated by parametric down-conversion can eliminate several sources of error that occur in single-beam measurements. In the correlated photon measurements, the down-converted photons are separated into two beams with one photon of a pair in each beam. The absolute detection efficiency of a detector in one beam can be determined from the count rate of a detector in the other beam and the coincidence rate for the two detectors. These ideas can be used to measure the optical absorbance of a sample placed in front of one of the detectors. Errors due to stray light and dark counts are substantially reduced and fluctuations in pump intensity largely eliminated.
Zhao
Zhi
Z
Chemical Sciences Division, Oak Ridge National Laboratory P.O. Box 2008, Oak Ridge, Tennessee 37831-6142, USA.
Meyer
Kent A
KA
Whitten
William B
WB
Shaw
Robert W
RW