Argon-ion, laser source

The difficulties of intensity-based flow cytometry are illustrated by the present difficulties of cell-by-cell measurements of intracellular calcium. This can be accomplished using the calcium probe Indo-l,(34 38) but requires an ultraviolet (UV) laser source which is not routinely available in flow cytometry (Indo-1 is an emission wavelength ratiometric probe). Flow cytometers routinely have argon ion laser sources with outputs of 488 or 514 nm. Measurement of intracellular ions other than Ca2+ is nearly impossible. (The SNAFL and SNARF probes should allow pH measurement from the wavelength-ratiometric data.(15))... 

FIGURE 18-7 Spectra of anthracene taken with a conventional Raman instrument with an argon-ion laser source at 514.5 nm (4) and with an FT-Raman instrument with a Nd-YAG source at 1064 nm H). (From B. Chase, Anal. Chem.. 1987. 59. 881 A. Figure 5, p. 888A. Copyright 1987 American Chemical Society.)... 

Since our main objective was to remove all the chlorine and hydrogen atoms from the polymer chain, C-PVC films were further exposed to the UV radiation of the medium pressure mercury-lamp. This led to a dark brown material w.hich was found to be unable to carry an electrical current, even after extended irradiation time. Therefore we turned to a powerful laser source, a 15 W argon ion laser tuned to its continuous emission at 488.1 nm. At that wavelength, the degraded polymer film absorbs about 30 % of the incident laser photons. The sample was placed on a X-Y stage and exposed to the laser beam at scanning rates in the range of 1 to 50 cm s, in the presence of air. 

Monochromatic light can also be obtained from other types of lasers solid state, gas, ion, dye. Among them argon ion laser with its many lines is an especially valuable light source used in many sensors. However, these types of lasers are expensive, the modulation of the light cannot be done internally and external modulators (e.g. choppers) should be used. Wavelengths emitted by some exemplary lasers are presented in Table 1. 

Figure 4. Photoacoustic signal measured in a sample liquid with an attached piezoelectric transducer having a resonant frequency of several tens of thousands of kilohertz. Note the change in scale of the amplitude and thus the much greater sensitivity of the detector at low light chopping frequencies. Argon ion laser light source, 400 mW, x = 488 nm sample 25 pg/mL BaSO powder suspended in aqueous glycerine. Reproduced with permission from Ref. 21 copyright 1980, American Chemical Society.

The commercially available laser source is a mode-locked argon-ion laser synchronously pumping a cavity-dumped dye laser. This laser system produces tunable light pulses, each pulse with a time duration of about 10 picoseconds, and with pulse repetition rates up to 80 million laser pulses/second. The laser pulses are used to excite the sample under study and the resulting sample fluorescence is spectrally dispersed through a monochromator and detected by a fast photomultiplier tube (or in some cases a streak camera (h.)) ... 

When compared to fluorescence detectors for HPLC, the design of a fluorescence detector for CE presents some technical problems. In order to obtain acceptable sensitivity, it is necessary to focus sufficient excitation light on the capillary lumen. This is difficult to achieve with a conventional light source but is easily accomplished using a laser. The most popular source for laser-induced fluorescence (LIF) detection is the argon ion laser, which is stable and relatively inexpensive. The 488-nm argon ion laser line is close to the desired excitation wavelength for several common fluorophores. The CLOD for a laser-based fluorescence detector can be as low as 10 12 M. 

The photochemical reaction was initiated with a UV source, and an argon-ion laser was used as the fluorescence excitation source (2 = 457.9 nm). A... 

In fluorescent detection, an argon ion laser is usually used for excitation. Suggest one fluorophore that is compatible with this source, and describe why there are two associated wavelengths. (3 marks)... 

The sample is introduced into the separation channel by electromigration injection. Thus far, detection has been solely by laser-induced fluorescence, using an argon ion laser or a helium/neon laser as the excitation source and a photomultiplier tube (PMT) or charge-coupled device (CCD)... 

The light source is an argon ion laser operated in a single-frequency mode. More than one watt of power can typically be obtained with a laser linewidth of approximately 10 MHz. The incident-beam polarization can be continually adjusted with respect to the scattering plane. 

Raman spectrometer with argon- or krypton-ion laser source liquid-sample cell or melting-point capillaries reagent-grade CCI4 safety goggles (such as those available from Glendale Optical Co., Woodbury, NY 11797). 

---