Ultra sensitive sensor with enhanced dynamic range for high speed detection of multi-color fluorescence radiation.

This paper describes design of the new ultra sensitive sensor system for fluorescence detection applications. System comprises two units: optical spectra separation unit and detection unit. Optical unit of the sensor performs spatial spectra separation of signal from the laser excited fluorescence, and resulting spectra is collected in the detection part of the system. Optical part is built using diffraction grating as spectra separation element. Detection part comprises 32-channel photomultiplier tube working in single photon counting mode with our 32-channel amplifier. Using single photon detection technique and specific signal processing algorithms for collected data, the proposed system allows to achieve unique combination of characteristics--high sensitivity, high detection speed and wide linearity dynamic range comparing to existing commercial instruments. DNA sequencing experiments with new sensor as detection device, and using two types of lasers (Ar-ion and Nd-YAG) were carried out, yielding sequencing traces which have quality factor of 20 for read lengths as long as 650 base pairs.

Hot electrons and curves of constant gain in long wavelength quantum well lasers.

In long wavelength quantum well lasers the effective electron temperature (T(e)) is often a strong function of the pump current and hence the T(e) correlates with the carrier concentration n in the active region. On the other hand, the material gain g in the active layer depends on both variables, g=g(n,T(e) ). We discuss a convenient way of analyzing this situation, based on considering the contours of constant gain g on the surface g(n,T(e) ). This is qualitatively illustrated with two model examples involving quantum well lasers, the long-wavelength quantum well laser with current dominated by the Auger recombination and the unipolar quantum cascade laser.