Excited laser spectral irradiance

Figure 17. Variation of laser-excited CN fluorescence intensity with laser spectral irradiance in a nitrous oxide-acetylene slot torch...

In LEI the matrix effects are low. This applies in particular to samples with complicated atomic spectra, as no spectral interferences are encounterd. Elements with low ionization energies may cause matrix effects. The latter could be due to a change in the ion current as a result of changes in the electron number density in the flame. This can be compensated for by measuring alternately with and without laser irradiation. Ionization of the matrix by the laser may also lead to errors in the ion currents measured. These can be eliminated by modulation of the frequency of the exciting laser radiation around v, which corresponds to E2 — = hv, where 2... 

In Raman measurements [57], the 514-nm line of an Ar+ laser, the 325-nm line of a He-Cd laser, and the 244-nm line of an intracavity frequency-doubled Ar+ laser were employed. The incident laser beam was directed onto the sample surface under the back-scattering geometry, and the samples were kept at room temperature. In the 514-nm excitation, the scattered light was collected and dispersed in a SPEX 1403 double monochromator and detected with a photomultiplier. The laser output power was 300 mW. In the 325- and 244-nm excitations, the scattered light was collected with fused silica optics and was analyzed with a UV-enhanced CCD camera, using a Renishaw micro-Raman system 1000 spectrometer modified for use at 325 and 244 nm, respectively. A laser output of 10 mW was used, which resulted in an incident power at the sample of approximately 1.5 mW. The spectral resolution was approximately 2 cm k That no photoalteration of the samples occurred during the UV laser irradiation was ensured by confirming that the visible Raman spectra were unaltered after the UV Raman measurements. 

The nature of the excited state decay processes is studied by the technique of laser flash photolysis, a full description of which has been given elsewhere (25). Briefly, flash photolysis involves irradiating a sample with a short (nanosecond) intense pulse from a laser, then observing by rapid response spectrophotometry the spectral changes that occur on the time scale nanoseconds to milliseconds. 

Most organometallic EDA complexes of arenes with titanium tetrachloride [116] in solution also follow the general reaction scheme in Eq. 15 in that no net chemical reaction is observed upon charge-transfer irradiation due to rapid back electron transfer (A et 10 ° s ). For example, the transient absorption spectrum of bro-moanthracene (BrAnt) cation radical generated by 532-nm laser excitation of the [BrAnt, TiCU] complex in cyclohexane (see Figure 7) decays completely to the spectral baseline within about 1 ns (see inset) due to back electron transfer [116], (Eq. 18) ... 

An application in photomedical research is the measurement of absorption and transmission of thick specimens e.g. human skin. A spectral narrowband irradiation of skin lesions and tumors can use the high spectral intensity together with the tunability of special lasers. Action spectra of phototherapeutic interest such as of photosensitizers like psoralens can be investigated. Furthermore, tunable lasers perform a selective excitation of practically any quantum state of atoms or molecules in the wavelength range from about 200 nm to 20 p. 

Laser lUman spectroscopy (LRS). The spectra were recorded on a Nicolet 950 FT-Raman spectrometer instrument, equipped with a nitrogen cooled Ge detector. A Nd YAG laser (1064 nm) was used as excitation source. The measurements were performed with a power at the sample of 100-200 mW in order to avoid decomposition and thermal effects. The samples were rotated to provide a noncontinuous irradiation of any given spot on the samples. The spectral slit width was typically 4 cm". ... 

All these phenomena can occur simultaneously within the same material, as illustrated by the spectral response of an oriented polymer doped with DCM dye (4-dicyanomethylene-2-methyl-6-p-dimethylamino-styryl-4H-pyran) under 1.06 iJ,m laser irradiation (Figure 1.1). The two sharp signals at 532 and 354 nm are coherent emission induced by SHG and THG, whereas the broad band is incoherent emission of two-photon excited fluorescence (TPEF). 

Using a mode-locked Nd + YAG laser system to generate picosecond sample excitation pulses and picosecond probing continuum pulses in their double beam spectrometer, Spalink et. al. (30) were able to measure difference absorption spectra of irradiated samples of 11-cis-rhodopsin and 9-cis-rhodopsin at selected times after excitation by means of a PAR OMA-2 optical multichannel detection system. The difference absorption spectral data were obtained over the entire spectral range from 410 nm to 650 nm at one time with an OMCD as opposed to the... 

The project Carl gave me was to build a sensitive instrument to search for luminescence from the permanganate ion, which had been the subject of a series of experimental single crystal absorption spectral studies and theoretical studies in the laboratory [6]. The spectrometer was built, but after repeated attempts using a range of crystals, excitation conditions and temperatures, no luminescence was detected. All subsequent efforts by others have confirmed this failure [7], under laser irradiation in iodide lattices some emission has been detected, but this is derived from the manganese ion MnO, 2 produced by a photoredox process [8]. This left me without many results to show for my year s work. I made some measurements on the intensely luminescent alkali metal platinocyanides but this did not lead to any new insights. 

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