Laser continuous wave emissions

Before the invention of lasers in 1960 (Maiman), radiation emitted by the mercury arc, especially at 435.8 and 404.7 nm, has been u.sed for exciting Raman spectra (Brandmiiller and Moser, 1962). Today, most types of lasers ( continuous wave (cw) and pulsed, gas, solid state, semiconductor, etc.), with emission lines from the UV to the NIR region, are used as radiation sources for the excitation of Raman spectra. Especially argon ion lasers with lines at 488 and 515 nm are presently employed. NIR Raman spectra are excited mainly with a neodymium doped yttrium-aluminum garnet laser (Nd YAG), emitting at 1064 nm. 

Both pulsed and cw (continuous-wave) emission are possible, although this book only deals with lasers which operate cw (or nearly so, as explained in Part II). 

Table I Influence of the beam focusing in the laser-graphitization of chlorinated PVC (continuous wave mode emission line at 488.1 nm of Ar+ laser)...

Some lasers produce a continuous-wave (CW) beam, where the timescale of the output cycle is of the same order as the time taken to remove photons from the system. CW lasers can be modified to produce a pulsed output, whereas other lasers are inherently pulsed due to the relative rates of the pumping and emission processes. For example, if the rate of decay from the upper laser level is greater than the rate of pumping then a population inversion cannot be maintained and pulsed operation occurs. 

Continuous wave operation of COIL is facilitated by the hyperfine structure of the atom. Iodine has a nuclear spin of, so the P /2 and Pz/2 levels are split by hyperfine interactions. Figure 8 shows the allowed transitions between the hyperfine sublevels and a high resolution emission spectrum. The F = 3 — F" = 4 transition is most intense, and this is the laser line under normal conditions. Collisional relaxation between the hyperfine sub-levels of Pz 2 maintains the population inversion, while transfer between the Fi/2 levels extracts energy stored in the F = 2 level. Hence, if it is not sufficiently rapid, hyperfine relaxation can limit power extraction. 

A theoretical study of the photolytic reaction of Ni(CO)4 using LCCTO-Xg has appeared, and the observed luminescence is assigned to emission from the charge-transfer excited fragment Ni(CO)3. Multiple luminescence has been observed from continuous wave laser irradiation of gas-phase Ni(CO)4 at room temperature. Two of the emissions are coupled in an... 

Here we present results of video-microscopy observations of the emission from silver nanoparticles (NPs) adsorbed on a glass substrate upon continuous-wave laser excitation and report what we believe to be the first experimental observation of memory in blinking dynamics of metal nanoparticles. 

Table 7.1 are continuous wave (CW), not pulsed. Second, frequency stability to < 1 cm" is important to assure Raman shift precision and avoid line broadening. Although the Raman shift axis is usually calibrated periodically, the laser frequency must remain stable between calibrations. Third, lasers vary significantly in output linewidth, from hundreds of reciprocal centimeters to much less than 1 cm". For the majority of samples of analytical interest, a laser linewidth below 1 cm" is sufficient. Laser linewidths are often quoted in terms of frequency rather than wavenumber, in which case 1 cm" equals 30 GHz. Lasers are available with < 1 MHz linewidths (< 10 em ), but such lasers would be unnecessarily narrow for most analytical Raman applications. Fourth, lasers differ in their output of light at wavelengths other than the laser line itself. Gas lasers (Ar+, Kr+, He-Ne) emit atomic lines (plasma lines), and solid-state lasers luminesce, both of which can interfere with Raman scattering. Essentially all lasers require a bandpass filter or monochromator to reduce these extraneous emissions. 

Time-resolved fluorometry fahs into one of two categories, depending on how the fluorescence emission response is measured (1) pulse fluorometry, in which the sample is illuminated with an intense brief pulse of light and the intensity of the resulting fluorescence emission is measured as a function of time with a fast detector system, or (2) phase fluorometry, in which a continuous-wave laser illuminates the sample, and the fluorescence emission response is monitored for impulse and frequency response. ... 

A continuous-wave green laser beam (argon ion laser, all lines) with a maximum power of up to 28 W is focused to the beam width of only 4 fim. As shown in Fig. 1, the vertically aligned laser beam runs orthogonal to the molecular beam. All molecules that pass the laser beam at or very close to the focus are heated to an internal temperature above 3000 K and ionize. The positive fullerene ions are then accelerated towards an electrode at 10 kV where they induce the emission of electrons. The electrons in turn are again multiplied and the charge pulses are subsequently counted. The overall molecule detection... 

The molecular species in a Broida oven can often be detected through their chemiluminescent emission [32], It is particularly convenient to monitor this emission in the early stages of a low-resolution analysis. The information that can be extracted from a chemiluminescent spectrum recorded with a monochromator is, however, limited. More typically, the molecules are detected by laser-induced fluorescence using either pulsed or continuous wave (CW) dye lasers. 

The room temperature luminescent spectra of sintered ceramic were recorded by a spectrofluorometer (Fluorolog-3, Jobin Yvon, Edision, USA) equipped with Hamamatsu R928 photomultiplier and a 450 W Xenon lamp. The upconversion luminescent spectra were measured by the same equipment using a 980 nm continuous wave diode laser as excitation source. All the emission spectra were corrected for the setup characteristic. 

MIRRORLESS CONTINUOUS WAVE LASER EMISSION FROM Nd YAG CERAMIC... 

Mirrorless Continuous Wave Laser Emission from Nd YAG Ceramic Waveguides... 

Note the presence of only one spot revealing the absence of parasitic reflections between parallel faces of the Nd YAG ceramic sample. The spectral distribution of the laser radiation was also measured. From the laser spectrum (not shown in this work for the sake of brevity) we have corroborated single mode laser oscillation with a linewidth of 0.25 nm., centered around 1064.4 nm peak. And, in this way, we have experimental proofs about spectral and spatial quality of continuous wave laser emission from Nd YAG ceramic waveguide structure. 

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