Characteristics of a Rubidium Metal Vapor Filter for Laser Scatter Rejection in Single Molecule Detection

Abstract

The characteristics of a rubidium metal vapor filter (MVF) for its use as a laser scatter filter for single molecule detection (SMD) were investigated. This investigation was done by a simulation along with experimental observation. A monochromator was used to elucidate the spectral components of the background in SMD. The major contributors to the background were laser transmission and fluorescence of the rubidium vapor. Experiments on the filter's performance under varying conditions such as MVF temperature, MVF pressure, and laser power were done. It was found that the integrated transmission intensity decreased with increasing pressure and temperature while it increased for increasing laser powers. The computer simulation modeled the experimentally observed profiles very well. Through the simulation, it was determined that the limitation on the attenuation by the MVF was due to the transmission of the broad-band stimulated emission “wings” of the Ti:sapphire laser.

Two-Channel Sequential Single-Molecule Measurement

“…Collimated light from MO1 was passed through a rubidium metal vapor filter (Rb-MVF) to selectively attenuate the significant scattered laser resonant radiation from the capillary. Details of the operation and characteristics of the MVF are published elsewhere . The MVF cell (Opthos, Rockville, MD) was heated to ∼150 °C in order to achieve a significant number density of rubidium atoms.…”

“…Details of the operation and characteristics of the MVF are published elsewhere. 30 The MVF cell (Opthos, Rockville, MD) was heated to ∼150 °C in order to achieve a significant number density of rubidium atoms. The Ti-sapphire laser was tuned to the 5 2 P 3/2 (780.023 nm) ground-state transition of the rubidium in the MVF using the intracavity birefringent filter and Fabry-Perot etalon within the Ti-sapphire laser.…”

“…The method is based on the premise that the laser line is narrower than the absorption profile of the metal so that laser scatter is attenuated to a large extent. Detailed theoretical and experimental characterization studies were performed in order to maximize the performance of the metal vapor filter .…”

“…Detailed theoretical and experimental characterization studies were performed in order to maximize the performance of the metal vapor filter. 30 Furthermore, this technique relied on the advantages gained in the reduction of background Raman scatter and fluorescence when working in the near-IR. 13 Despite all of its analytical advantages, obtaining nearunity measurement efficiency has come at the expense of a lower SNR compared with other SMD techniques.…”