Lasers step tunable

STEP TUNABLE LASER - OA ABSORPTION POLLUTION DETECTION... 

By employing a laser for the photoionization (not to be confused with laser desorption/ ionization, where a laser is irradiating a surface, see Section 2.1.21) both sensitivity and selectivity are considerably enhanced. In 1970 the first mass spectrometric analysis of laser photoionized molecular species, namely H2, was performed [54]. Two years later selective two-step photoionization was used to ionize mbidium [55]. Multiphoton ionization mass spectrometry (MPI-MS) was demonstrated in the late 1970s [56—58]. The combination of tunable lasers and MS into a multidimensional analysis tool proved to be a very useful way to investigate excitation and dissociation processes, as well as to obtain mass spectrometric data [59-62]. Because of the pulsed nature of most MPI sources TOF analyzers are preferred, but in combination with continuous wave lasers quadrupole analyzers have been utilized [63]. MPI is performed on species already in the gas phase. The analyte delivery system depends on the application and can be, for example, a GC interface, thermal evaporation from a surface, secondary neutrals from a particle impact event (see Section 2.1.18), or molecular beams that are introduced through a spray interface. There is a multitude of different source geometries. 

The present research has treated important parts of the modeling of combustion and NOx formation in a biomass grate furnace. All parts resulted in useful approaches. For all these approaches successful first steps were taken. Currently, more research is underway to obtain improved results NH3 production is measured in the grid reactor with the tunable diode laser, detailed kinetics will be attached to the front propagation model, including the measured NH3 release functionalities, and for the turbulent combustion model heat losses are taken into account. In addition, the fuel layer model has to be coupled to the turbulent combustion model in the furnace. 

As mentioned in the introduction, a major advantage that Fourier transform spectroscopy has over laser spectroscopy is that it is straightforward to record the entire spectrum of a species at once. Diode lasers in the infrared are not continuously tunable and have mode gaps which can only be filled by switching diodes. Many ultraviolet lasers are not continuously tunable either. Tunable difference frequency methods and diode lasers involve much longer scan times than are necessary with a Fourier transform device. For example, the Bomem DA3.002 can scan a bandwidth of 100 or more wavenumbers in the mid-IR at a resolution of 0.005 cm-1 in less than 3 minutes. A diode laser which scans in 20 MHz steps may require more than a day to scan the same spectral region. 

There are a number of applications where it might be favorable to use optically driven organic semiconductor lasers without the need for additional processing steps. Easy to fabricate and thus cost-effective disposable devices are highly attractive, tunable laser sources for single-use spectroscopy applications, e.g. in medicine and biotechnology. 

Emissions from both the and the previously unreported lli states of the IF molecule have been observed in the gas-phase reaction of L with F2 at low pressure a four-centre complex has been proposed as the reaction intermediate. A combined theoretical-experimental programme has been conducted to establish techniques for the study of excited-state transitions in Ij and IC1. Experimental techniques based on two-step excitation using two synchronized, tunable lasers have been developed, and successfully applied to excited-state fluorescence measurements on ICl. lodine(i) chloride adsorbed on silica gives the same Raman spectrum as that obtained from adsorbed l2. ... 

Time-resolved infrared spectroscopy (TRIR) has been outstandingly successful in identifying reactive intermediates and excited states of both metal carbonyl [68,69] and organic complexes in solution [70-72]. Some time ago, the potential of TRIR for the elucidation of photochemical reactions in SCFs was demonstrated [73]. TRIR is particularly suited to probe metal carbonyl reactions in SCFs because v(CO) IR bands are relatively narrow so that several different species can be easily detected. Until now, TRIR measurements have largely been performed using tunable IR lasers as the IR source and this has restricted the application of TRIR to the specialist laboratory [68]. However, recent developments in step-scan FTIR spectroscopy promise to open up TRIR to the wider scientific community [74]. 

Several gas-phase diagnostic studies have been performed especially on the hot-filament CVD process in an attempt to analyze the spatial distribution of stable and reactive species in the region between filament and substrate and to obtain information about the decisive steps in the diamond formation mechanism. One of the first quantitative investigations of this kind was performed by Celii et al. using tunable infrared-laser detection of methane, acetylene, ethylene and methyl [54,551. Aside from a considerable conversion of methane (starting concentration 8 X 10 " cm ) to acetylene (2 x lO cm" ) near the hot filament (tungsten, 2200°C), methyl radicals were found with a concentration of 2 x lO cm". ... 

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