Raman laser

With commercially available YDFL as pumps, powers > 40 W at 1178 nm are feasible. This sets an upper limit to the conversion efficiency needed in the subsequent second harmonic generation. Numerical simulations for the amplifier and resonator Raman laser configuration indicate feasibility of the system with sufficient SBS suppression. ESO has assembled the amplifier configuration, and has demonstrated up to 4 W CW at 1178 nm. ESO s goal is to have compact and turnkey commercial fiber lasers for LGS/AO within 3 years. 

This report has been written in order to demonstrate the nature of spin-state transitions and to review the studies of dynamical properties of spin transition compounds, both in solution and in the solid state. Spin-state transitions are usually rapid and thus relaxation methods for the microsecond and nanosecond range have been applied. The first application of relaxation techniques to the spin equilibrium of an iron(II) complex involved Raman laser temperature-jump measurements in 1973 [28]. The more accurate ultrasonic relaxation method was first applied in 1978 [29]. These studies dealt exclusively with the spin-state dynamics in solution and were recently reviewed by Beattie [30]. A recent addition to the study of spin-state transitions both in solution and the... 

Apart from LIF, other laser-based HPLC detectors are LS and Raman. Laser spectroscopic methods for detection in LC have been reviewed [567]. 

TLC-Raman laser microscopy (X = 514 nm) in conjunction with other techniques (IR microscopy, XRF and HPLC-DAD-ESI-MS) has been used in the analysis of a yellow impurity in styrene attributed to reaction of the polymerisation inhibitor r-butylcatechol (TBC) and ammonia (from a washing step) [795]. Although TLC-FT-Raman did not allow full structural characterisation, several structural elements were identified. Exact mass measurement indicated a C20H25O3N compound which was further structurally characterised by 1H and 13C NMR. 

The compound and its methyl homologue exploded occasionally when scraped from the walls of a tube, and invariably when exposed to a Raman laser beam, even at — 80° C. 

Occasionally the dry product exploded violently when scraped off the glass container. It invariably exploded when irradiated with a Raman laser beam, even at —80°C. 

Kippenberg, T.J., Spillane, S.M., Armani, D.K., and Vahala K.J., 2004, Ultralow-threshold microcavity Raman laser on a microelectronic chip, Opt Lett. 29(11) 1224-1226. 

Spillane, S.M., Kippenberg, T.J., and Vahala, K. J., 2002, Ultralow-threshold Raman laser using a spherical dielectric microcavity, Nature 415 (6872) 621-623. 

S.D. Harvey, T.J. Peters and B.W. Wright, Safety considerations for sample analysis using a near-infrared (785 nm) Raman laser source, Appl. Spectrosc., 57, 580-587 (2003). 

SPIN FLIP RAMAN LASER OPTO-ACOUSTIC SPECTROMETER... 

Raman earth halide clusters, 46 2-3 Raman laser temperature-jump technique, 32 17-18... 

A major advance in the investigation of the intramolecular dynamics of spin equilibria was the development of the Raman laser temperature-jump technique (43). This uses the power of a laser to heat a solution within the time of the laser pulse width. If the relaxation time of the spin equilibrium is longer than this pulse width the dynamics of the equilibrium can be observed spectroscopically. At the time of its development only two lasers had sufficient power to cause an adequate temperature rise, the ruby laser at 694 nm and the neodymium laser at 1060 nm. Neither of these wavelengths is absorbed by solvents. Various methods were used in attempts to absorb the laser power, with partial success for microsecond relaxation times. 

Fig. 2. Schematic diagram of the Raman laser temperature-jump experiment.

The Raman laser temperature-jump technique has been used in studies of a variety of spin-equilibrium processes. It was used in the first experiment to measure the relaxation time of an octahedral spin-equilibrium complex in solution (14). Its applications include investigations of cobalt(II), iron(II), iron(III), and nickel(II) equilibria. 

The dynamics of an octahedral spin equilibrium in solution was first reported in 1973 for an iron(II) complex with the Raman laser temperature-jump technique (14). A relaxation time of 32 10 nsec was observed. Subsequently, further studies have been reported with the use of this technique, with ultrasonic relaxation, and with photoperturbation. Selected results are presented in Table III. 

Methods T, Raman laser temperature-jump U, ultrasonic relaxation P, photoperturbation. 

Consideration of the thermodynamics of a representative reaction coordinate reveals a number of interesting aspects of the equilibrium (Fig. 5). Because the complex is in spin equilibrium, AG° x 0. Only complexes which fulfill this condition can be studied by the Raman laser temperature-jump or ultrasonic relaxation methods, because these methods require perturbation of an equilibrium with appreciable concentrations of both species present. The photoperturbation technique does not suffer from this limitation and can be used to examine complexes with a larger driving force, i.e., AG° 0. In such cases, however, AG° is difficult to measure and will generally be unknown. 

The spin-equilibrium dynamics of iron(III) complexes in solution have been examined with the techniques of Raman laser temperature-jump, ultrasonic relaxation, and photoperturbation. The complexes investigated, the relaxation times observed, and one of the derived rate constants are presented in Table IV. Many of the relaxation times are quite short, and some of the original temperature-jump results (45) were found to be inconsistent with more accurate ultrasonic experiments (20) and later photoperturbation experiments (102). It has not been possible to repeat some of these laser temperature-jump observations. Instead, the expected absorbance changes and isosbestic points were found to occur within the heating rise time of the laser pulse, consistent with the ultrasonic and photoperturbation experiments (20). Consequently, none of the original Raman laser temperature-jump results is included in Table IV. 

This prediction is confirmed by observation of a very rapid relaxation of the spin equilibrium in Co(terpy)22+ in solution. A relaxation time of less than 15 nsec was observed in a Raman laser temperature-jump experiment (14). This is consistent with the absence of any relaxation of the small excess sound absorption found in ultrasonic experiments. An upper limit of 0.2 nsec for the relaxation time in water at 298 K can be calculated from the magnitude of the excess absorption, which is... 

Harvey, S.D. Peters, T.J. 8t Wright, B.W. Safety Considerations for Sample Analysis Using a Near-Infrared (785 nm) Raman Laser Source Appl. Spectrosc. 2003, 57, 580-587. 

As discussed in more detail in Section 3.2.18, Raman laser scattering detects low concentrations of various gases (Figure 3.17). Finally, the refractive index (RI) fiber-optic probe compares the RI of the process material with that of its prism and measures the reflected light as an indication of process RI. 

In all the above processes, only the first one ( + ) is a photochemical change while the rest (— ) are nonradiative chemical changes. It should be mentioned that the first step does not have to be photochemically induced for the methods discussed here to be applicable. Heat pulses or electric field pulses could provide the initial perturbation that changes A into the other intermediates that are to be identified by using a probe Raman laser. 

Normal Raman laser excitation in the visible and NIR region (52) can be used to obtain the SERS effect. The substrate surface is extremely important in providing the necessary enhancement to make the technique as valuable as it has become. A number of substrates have been used (53). These include evaporated silver films deposited on a cold surface at elevated temperature ( 390 K) on a glass substrate, photochemically roughened surfaces (e.g., silver single crystals subjected to iodine vapor, which roughens the surface), grating surfaces, and mechanically abraded and ion-bombarded silver surfaces. 

XRD, X-ray diffraction XRF, X-ray fluorescence AAS, atomic absorption spectrometry ICP-AES, inductively coupled plasma-atomic emission spectrometry ICP-MS, Inductively coupled plasma/mass spectroscopy IC, ion chromatography EPMA, electron probe microanalysis SEM, scanning electron microscope ESEM, environmental scanning electron microscope HRTEM, high-resolution transmission electron microscopy LAMMA, laser microprobe mass analysis XPS, X-ray photo-electron spectroscopy RLMP, Raman laser microprobe analysis SHRIMP, sensitive high resolution ion microprobe. PIXE, proton-induced X-ray emission FTIR, Fourier transform infrared. 

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