Optics Research at NIST
In Summer 2000, I participated in the REU program at the National Institute of Standards and Technology (Gaithersburg, MD), where I characterized and calibrated optical trap detectors. These detectors are used to transfer the national standard for optical power to other instruments. The silicon photodiodes in an optical trap detector are arranged to trap nearly all light focused into the detector aperture, converting absorbed photons to a measurable electric current. An ideal detector would have a uniform response across its active area and would have the same output when the light source it is measuring changes incident angle or polarization. Dust, humidity, and manufacturing imperfections, however, can limit the uniformity of the photodiodes.
To study the uniformity of the detectors, I mounted them on electronically controlled stages and focused a stabilized HeNe laser inside their aperture. I wrote LabVIEW programs to control the spatial and angular position of the detector and collected the output of the detector at each new position. This allowed me to create two-dimensional uniformity mappings by scanning the aperture with a beam perpendicular to the detector face, and to measure the angular sensitivity of the detectors by focusing the beam in the center of the aperture and rotating the detector. I also performed some calibration repeatability measurements and designed an experiment for polarization sensitivity tests.
This work was acknowledged in J. Houston et al., J. Res. Natl. Inst. Stand. Technol. 106, 641 (2001).