Wavelengths absorbed

Laser removal of tattoos and of colored birthmarks has been widely studied. A high power pulsed laser at a wavelength absorbed by the pigment is used to vaporize the pigment and to bleach the colored area. Ruby, Nd YAG, and dye lasers are favored for this purpose. 

Optical methods of analysis are dependent either upon (i) measurement of the amount of radiant energy of a particular wavelength absorbed by the sample, or (ii) the emission of radiant energy and measurement of the amount of energy of a particular wavelength emitted. Absorption methods are usually classified according to the wavelength involved as (a) visible spectrophotometry (colorimetry), (b) ultraviolet spectrophotometry, and (e) infrared spectrophotometry. 

The products of the photodecomposition of the ferrioxalate absorb only weakly at wavelengths absorbed by ferrioxalate and therefore provide no problem with regard to a product filter effect. This can be seen from Table 2.7. 

Relatively long wavelength absorbers are utilized to maximize the capture of the solar spectrum. 

Scheme 14. Benzoylterrylenmonoimide 50 A dye with a long wavelength absorbance maximim at 676 nm.

Different studies performed with purpurinimides, a reduced macrocycle that showed a long wavelength absorbance, by Pandey and co-workers67,71... 

It is fluorescence because a longer wavelength (lower energy) is emitted than the wavelength absorbed. 

Once the control and experimental light transmissions were balanced at an appropriate wavelength, absorbing in the experimental system could be monitored at a different wavelength suitable for the component under investigation. Measurements were thus made in intact, actively respiring organelles. 

If, however, aerated solutions of polynucleotides containing any one of a variety of dyes are exposed to light of a wavelength absorbed by the dye, guanine (18) is selectively oxidized. Adenine (19) is unaffected, and the effect on the pyrimidines is, for most dye sensitizers, slight or nil. 

Atomic absorption spectrometry (AA). This is a standard laboratory analytical tool for metals. The metal is extracted into a solution and then vaporized in a flame. A light beam with a wavelength absorbed by the metal of interest passes through the vaporized sample for example, to measure zinc, a zinc resonance lamp can be used so that the emission and absorbing wavelengths are perfectly matched. The absorption of the light by the sample is measured and Beer s law is applied to quantify the amount present. 

Figure 3 shows representative single-wavelength absorbance transients for three dyes electrostatically bound to colloidal Sn02. The transients correspond to photoinitiated bleaching and recovery of the respective MLCT absorbances. From Fig. 3, it is clear that (1) injection is rapid in comparison to backET, (2) back ET is complex kinetically, but (3) the complex recovery rates depend strongly on the identity of the dye, at least in the first few hundred nanoseconds of the recovery. In order to isolate the shorter-time recovery kinetics, transients were fit, somewhat pragmatically, to a bi-exponential decay function ... 

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