We have built several flow cytometers (FCMs) which incorporate the principle of light collection using a flow- stream waveguide (FSW). The smallest and most rugged version uses a diode laser emitting 820-nm light and collects perpendicular light scatter (PLS) with the FSW technique and collects forward light scatter (FLS) with a simple external lens. Both PLS and FLS detectors are silicon diodes with integral preamps; no fluorescence is collected. Two other units have used argon-ion lasers and a dichroic filter to separate PLS and fluorescence, and our studies have examined the factors which limit the performance of FSW light collection for low-level-fluorescence applications. In one case we have used a main-frame laser with line-tunable output and two cylindrical lenses for focusing onto the flow stream. This arrangement has allowed us to detect 93-nm yellow-green beads from Molecular Probes, Inc. and 140-nm green beads from Duke Scientific, Inc. A more recent 'luggable' version incorporates an air-cooled ion laser and a simple spherical lens for focusing the laser onto the flow stream. This FCM was able to detect the 93-nm beads from Molecular Probes. In all cases a flow stream in air is used as an optical waveguide that traps and transports light to one or more detectors.
This paper reports on the operation of lithium niobate electro-optic waveguide modulators at temperatures down to 15 degree(s)K. Commercial and laboratory fiber pigtailed devices have successfully been cooled without any increases in insertion loss from temperature induced stresses in device packaging. Three x-cut devices exhibited a linear increase in Vpi voltage of 8% +/- 1% when cooled from room temperature to approximately 20 degree(s)K. The broadband frequency response improved at lower temperatures. A velocity-matched experimental modulator has shown increased bandwidth when cooled to liquid nitrogen temperature.