Frequency tripling

A similar calculation will show that the stimulated Raman effect applied to frequency tripled radiation from a Nd YAG laser, with a fundamental wavelength of 1064.8 nm, produces wavelengths of 299 nm, with H2, and 289 nm, with H2. 

The third term in equation 12 corresponds to frequency tripling, which leads to an output at 355 nm for a Nd YAG laser. The coefficient may be... 

For ion TOF measurement a probe laser was used to ionize reaction products in the reaction zone. The (1 + F) resonance-enhanced multiphoton ionization (REMPI) method was adapted for H-atom detection. The necessary vacuum ultraviolet (VUV) radiation near 121.6 nm (for Lyman-a transition) can readily be generated by a frequency-tripling technique in a Kr cell.37 The sensitivity of this (1 +1 ) REMPI detection scheme is extremely high owing to the large absorption cross-section of Lyman-a transition,... 

For comparison purposes, two other MS systems have been used with in vitro grown parasite cultures. In the first case, a home-built miniaturized linear TOF multi-array analyzer1718 was interfaced to the frequency-tripled output at 355nm of a Q-switched Nd-YAG laser ( Polaris, New Wave Research, Fremont, CA). In this experiment the laser beam was not scanned, and the estimated laser fluence after attenuation was similar to that of the commer-... 

Cr(CO)5 interacts with solvent molecules and in solution cannot be considered as naked. The interaction is much weaker with fluorocarbon solvents than hydrocarbon 33). Using a pulsed laser photolysis source (frequency tripled NdYAG) and C7F14 as a solvent, Kelly and Bonneau 33) measured the rate constants for the reaction of Cr(CO)5 with C6H12, CO, and other ligands [Eq. (3)]. 

It is evident that the polarization contains a frequency doubled component (2co), a frequency tripled component (3co), and so on. 

Both LDI and MALDI make use of the absorption of laser light by a solid sample layer. The energy uptake upon laser irradiation then causes evaporation and ionization of the sample. Wavelengths ranging from ultraviolet (UV) to infrared (IR) have been employed, e.g., nitrogen lasers (337 nm), excimer lasers (193, 248, 308 and 351 nm), Q-switched, frequency-tripled and quadrupled Nd Yag lasers (355 and 266 nm, respectively), [24] Er Yag lasers (2.94 pm) [24,25] and TEA-CO2 lasers (10.6 pm). [16,26]... 

In addition to the blueshifling of the optical absorbance of Q-state semiconductor particles, a linear optical effect, there are nonlinear optical effects demonstrated by Q-state semiconductors. Two types have been observed by MCs prepared in organized films. One is the third harmonic generation or frequency tripling (44). A... 

Finally, the nonlinear polarizability of dyes is used for frequency tripling the output of high-power lasers. 

The nonlinear absorption of dyes will be treated first, followed by a description of the various applications making use of this property. Dye lasers will be examined next, but only briefly, since a monograph on dye lasers has recently been pub-fished 3>. Finally, frequency tripling in dyes will be considered. 

This scheme of frequency tripling was successfully tested with fuchsin in hexafluorisopropanol (a solvent selected for its low index of refraction and relatively flat dispersion curve) to frequency-triple the output of a neodymium laser 67,68) With an input power of 10 MW/cm2 a third-harmonic output of 0.2 mW/cm2 was measured. This low value was mainly due to the relatively high absorption of fuchsin at 355 nm. An improvement of the efficiency by a factor of 80 was found with hexamethylindocarbocyanine iodide in hexafluorisopropanol because of the much lower absorption of this dye at 355 nm. Since the absorption minimum of this dye is at 383 nm, one could expect an additional efficiency increase by a factor of 70 for a fundamental laser wavelength of 1.15 / 69>. Other cyanine dyes have been used for frequency tripling a fundamental wavelength of 1.89 /mi 70>. 

A further improvement and more freedom in the choice of laser wavelengths can be expected with the use of dye vapors. In liquids, the phase-matching concentration is set by the requirement that the anomalous dispersion of the dye compensates for the normal dispersion of the solvent. The latter is a new parameter that can be varied at will in the gas phase by changing the nature and partial pressure of the buffer gas. The broader resonances of dyes as opposed to metal vapors, which are sometimes used for this purpose, is an advantage for tunable frequency tripling of dye lasers. Another advantage results from the possibility of working at much lower temperatures than with metal vapors. 

The laser system consists of two dye lasers (Spectra Physics PDL 3) pumped by a single Nd-YAG laser (Quanta Ray GCR 270). Dye Laser 2, pumped at 355 nm, operates in these experiments in the range 370-500 nm (5-15 mJ/pulse), whereas Dye Laser 1, pumped at 532 nm, operates at 660-600 nm and is frequency tripled using KD P and BBO crystals... 

The linear susceptibility yy1 1 is related to optical refraction and absorption. The most common effects due to second-order susceptibility x(2) are frequency doubling x (-2co co, co) and the EO (Pockels) effect x(2)(- 0, co). The third-order susceptibility y 3) is responsible for such phenomena as frequency tripling and the Kerr effect. 

The fundamental component (aE) is linear in E and represents the linear optical properties discussed above. The second (jfiE-E) third ( yE-E-E) and subsequent harmonic terms are nonlinear in E and give rise to NTO effects. The / and values are referred to, respectively, as the first and second hyperpolarisabilities. The second harmonic term gives rise to second harmonic generation (SHG), the third results in frequency tripling effects, and so on. Importantly, since only the time-averaged asymmetrically induced polarisation leads to second-order NLO effects, the molecule and crystal must be non-centrosymmetric, otherwise the effects will cancel one another. Third-order effects, however, may be observed in both centrosymmetric and non-centrosymmetric materials. 

The dielectric tensor describes the linear response of a material to an electric field. In many experiments, and particularly in optical rheometry, anisotropy in is the object of measurement. This anisotropy is manifested as birefringence and dichroism, two quantities that will be discussed in detail in Chapter 2. The nonlinear terms are responsible for such effects as second harmonic generation, electro-optic activity, and frequency tripling. These phenomena occur when certain criteria are met in the material properties, and at high values of field strength. 

Fig. 25. Time resolved CIDNP spectrum observed upon photo-induced electron transfer oxidation of hexamethyl-(Dewar)-benzene (0.02 M) by chloranil (0.02 M). The top spectrum was observed 5 ps after excitation with the frequency-tripled output (355 nm) of a Nd/YAG laser. The bottom spectrum was recorded in the dark...

The laser system consists of a Continuum Powerlite Precision 9010 Nd YAG with a 5-ns pulse width and a repetition rate of 10 Hz. The 118.2nm light, equivalent to a photon energy of 10.49 eV, is produced by frequency tripling the third harmonic output (354.6 nm) of the Nd YAG laser. To accomplish this, the 354.6 nm laser beam is focused into a stainless steel tripling cell filled with Xe or Xe/Ar mixtures, which is attached directly to the ion source of the mass spectrometer. Figure 7 shows a schematic diagram of the SPI-TOF-MS instrument. 

Simonson et al. [148] demonstrated remote detection of explosives in soil by combining distributed sensor particles with UV/vis fluorescence LIDAR technology. The key to this approach is that the fluorescence emission spectrum of the distributed particles is strongly affected by absorption of nitroaromatic explosives from the surrounding environment. Remote sensing of the fluorescence quenching by TNT or DNT is achieved by fluorescence LIDAR - the emission spectra were excited in field LIDAR measurements by a frequency-tripled Nd YAG laser at 355 nm and the fluorescence collected with a telescope and various detector systems housed in a 10 x 50 trailer. TNT has been detected in the ppm range at a standoff distance of 0.5 km with this system (Fig. 16). An important limitation to this technique is the pre-concentration of the explosives on the sensor particles, which requires the presence of water to facilitate the transport of the explosive from the surface of the soil particles to the sensor particles. 

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