Development of ultra-low-noise spectrophotometry for analytical applications

Methodology and instrumentation that dramatically increase the signal-to-noise ratio of scanning spectrophotometers over present commercial instruments is presented. The increase was accomplished by greatly reducing all important noise components. The random noise from an incoherent light source, which is the dominant noise source for most commercial spectrophotometers, was effectively removed by use of unique noise cancellation circuitry implemented with a dual-beam spectrophotometer configuration. Several other noise sources were also minimized by appropriate instrumental design, so that the observed noise level was attributable to the shot noise of the detectors. Single-wavelength measurements taken with a home-built prototype instrument have achieved a signal-to-noise ratio increase near 100-fold over commercial instruments. A spectrum taken in the visible region with a home-built retrofit detector installed in a commercial instrument showed a 10-fold signal-to-noise ratio increase over the standard commercial instrument. Widespread implementation of the methodology should enable many new types of research activities.