Laser detector

Laser detector Digital audio disks, video disks, laser-beam position sensors, distance sensors... 

Drushel [58] and others [31,59] have described the needs of the chromatographer in the area of detectors. Specific texts concern detection in quantitative GC [54], diode-array detection in HPLC [48], selective detectors [39] and element-specific chromatographic detection by AES [60], electrochemical detectors [61] and laser detectors [62]. 

DNA samples are introduced into the 96-capillary array. When the samples are separated through the capillaries, the fragments are irradiated with laser hght. A charge coupled device measures the fluorescence and acts as a multichannel detector. The bases are identifled in order in accordance to the time required for them to reach the laser-detector region. 

Belenkii BG. Use of laser detectors in capillary liquid-chromatography. Journal of Chromatography. Biomedical Applications 434, 337-361, 1988. 

Dramatic improvements in instrumentation (lasers, detectors, optics, computers, and so on) have during recent years raised the Raman spectroscopy technique to a level where it can be used for species specific quantitative chemical analysis. Although not as sensitive as, for example IR absorption, the Raman technique has the advantage that it can directly measure samples inside ampoules and other kinds of closed vials because of the transparency of many window materials. Furthermore, with the use of polarization techniques, one can derive molecular information that cannot be obtained from IR spectra. Good starting references dealing with Raman spectroscopy instruments and lasers are perhaps [34-38]. 

Some electronic spectroscopies take particular advantage of the remarkable coherency, brightness, directionality, and spectral purity of laser sources or the extreme sensitivity and/or rapid response times of modem fight detectors. Potent laser/detector combinations, when coupled to an... 

One of the earliest efforts of qualitative measurement of a protein (human serum albumin) in a microchip-based device was based on bead agglutination in a microchamber (approximately lOjaL). Subsequently, several quantitative immunoassays have been performed using microchip electrophoretic systems that permit separation and quantitation of free- and bound-labeled antigens in competitive assays (see Chapter 5). Most are carried out in channels micro-machined into fused silica substrates. Early work on quantitative assays achieved measurement of cortisol in serum.The assay used cortisol labeled with fluorescein and an argon laser detector at 488 nm and required only 80 pL of a 40x dilution of serum as the sample. Other capillary electrophoresis-based assays for a variety of antibodies have also been developed that include immunoglobulins (IgG, IgA, and IgM), antibovine serum albumin, and antiestradiol. ... 

The operation of FTIR spectrometers has been described in detail elsewhere, (see, for example. Refs. [4, 64]), as have the advantages of these over dispersive instruments [4, 5, 64]. Briefly, the heart of an FTIR spectrometer is the Michaelson interferometer (MI) (Fig. 6). The infrared beam leaves the source, S, and is incident on a beam-splitter, B. Fifty percent of the light is transmitted to a moving mirror, MM, and 50% to a fixed mirror, FM. On reflection, these rays recombine and interfere at the beam-splitter before reaching the detector, D, via the window, W, and reflective working electrode, WE, of the spectroelectrochemical cell. The system also includes a reference laser, RL, which follows the same path through the interferometer, after which it is intercepted and directed at the laser detector, LD. 

B, beam-splitter Di detector FM, fixed mirror IR, infrared beam L, laser beam LD, laser detector Ml, Michaelson interferometer MM, moving mirror ... 

Thin film on heat sink lO- " 10 D 30 ms as above Fast laser detector... 

Cannes advantage. All FTIR instruments make use of a He-Ne laser beam coaxial with the infrared beam. A separate laser detector triggers data collection at every zero-crossing of this signal—i.e. when the interferometer has introduced the maximum destructive interference into the modulated laser beam. 

Laser detectors operate in a similar way to optical beam detectors. The laser beam is directed across the area to be protected and is deflected or obscured by either the heat, the flame or the smoke rising from a fire, thus changing the intensity of lighf at the receiver. This triggers the alarm. 

Evolution of (a) product temperature at vial bottom as detected by thermocouples and (b) water concentration in chamber gas as measured by a laser detector. The vertical line indicates the endpointtimefor ice sublimation. 

As was alluded to in the previous subsection, proper configuration of the analyzer package is a crucial factor in the system s function and acceptance in the process environment. Raman analyzers have several key components, which include the laser, detector, and spectrograph, that must be appropriately packaged in a reliable on-line analyzer. 

Obviously, this problem would be alleviated if ADCs of higher dynamic range were used. Although 18-bit ADCs are commercially available, they are typically slower and more expensive than their 16-bit counterparts. A relatively recent development has been the introduction of the sigma-delta ADCs (see Section 3.4). These devices have an effective dynamic range of about 21 bits but sample the signals from the infrared and laser detectors simultaneously at equal intervals of time rather... 

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