Tunable laser sources

Improvements in technology will shape developments in PL in the near future. PL will be essential for demonstrating the achievement of new low-dimensional quantum microstructures. Data collection will become easier and ter with the continuing development of advanced focusing holographic gratir, array and imaging detectors, sensitive near infiared detectors, and tunable laser sources. 

For 2PA or ESA spectral measurements, it is necessary to use tunable laser sources where optical parametric oscillators/amplifiers (OPOs/OPAs) are extensively used for nonlinear optical measurements. An alternative approach, which overcomes the need of expensive and misalignment prone OPO/OPA sources, is the use of an intense femtosecond white-light continuum (WLC) for Z-scan measurements [71,72]. Balu et al. have developed the WLC Z-scan technique by generating a strong WLC in krypton gas, allowing for a rapid characterization of the nonlinear absorption and refraction spectra in the range of 400-800 nm [72]. 

This section is focused primarily on source and detector technologies. For some applications the source or the detector actually defines the entire measurement technology, for example tunable lasers (source) and array spectrographs (detector). There are other important technologies to consider, especially in the area of data acquisition, control, computer, and commuiucation technologies. These are rapidly changing areas, and if viewed genericaUy, service all forms of instrumentation. Where practical, compaiues tend to use standard platforms, but for certain applications, where performance is critical, there is still a case for proprietary solutions. 

Most optical spectral measurements, where the measurement of multiple wavelengths is required, will feature some type of polychromatic or broadband light source. There are a few exceptions here, such as tunable laser sources and source arrays. In such instances, the source is effectively "monochromatic at a given point in time. These sources are covered separately under monochromatic sources. 

The use of tunable lasers as sources in electronic absorption and emission spectroscopy has made possible a very considerable increase in resolution and precision. Electronic spectra are often difficult to analyze because of the many transitions involved. However, with a tunable laser source, one can tune the laser frequency to a specific absorption frequency of the molecule under study and thus populate a single excited electronic vibration-rotation energy level the resulting fluorescence emission spectrum is then simple, and easy to analyze. 

Accordingly, it was very soon found that using sources for which the physical widths of the emitted analyte lines are low is more attractive. This is necessary so as to obtain high absorbances, as can be understood from Fig. 76. Indeed, when the bandwidth of the primary radiation is low with respect to the absorption profile of the line, a higher absorption results from a specific amount of analyte as compared with that for a broad primary signal. Primary radiation where narrow atomic lines are emitted is obtained with low-pressure discharges as realized in hollow cathode lamps or low-pressure rf discharges. Recently, however, the availability of narrow-band and tunable laser sources, such as the diode lasers, has opened up new per-... 

One of the important applications of second-order NLO materials is obtaining of tunable laser sources. Second harmonic generation or sum frequency generation systems lead to monochromatic sources. The optical parametric oscillators are based on the parametric generation of two waves with frequencies co (signal) and CO (idler). In noncentrosymmetric materials an incident photon with frequency co creates two photons satisfying the energy... 

It is admitted that spectroscopy in the far-infrared suffers from the lack of more powerful sources and more sensitive detectors 2 ). Here Fourier transform spectroscopy has some advantages over conventional spectroscopy, e.g. with a grating instrument, and will probably be the most used method until coherent tunable laser sources take over. 

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. 

In fact, dimers are often interesting and important. For example, alkali dimers are thought to undergo triplet-triplet electronic transitions which are excimer-like, in the sense that the lower state is repulsive (cf section 2.27). They are therefore potentially useful as broadband tunable laser sources [652, 653]. 

Addition of a tunable laser source to the system enhances the capability for film characterization. Depth profiling measurements are possible on films that exhibit significant optical absorption near the laser excitation wavelength. The penetration depth of the probe laser decreases as it is tuned to shorter wavelengths, selectively exciting Raman... 

The electronic spectra for fluorescein and rhodamine, shown in Figures 9.4 and 9.5, respectively, illustrate the utility of having a tunable laser source. Not only does this facility enable the construction of absorption type spectra (PD action spectra or excitation spectra) but, for fluorescence studies, it is useful to be able to tune the excitation wavelength so as to excite the system of interest in the most... 

The medium infrared spectral region contains typically vibrational transitions of molecules and their rotational substructure. Therefore it is obvious, that one can use vibration rotation transitions in a laser medium itself, provided there is an inversion mechanism available. However, in the gas phase such transitions are fairly narrow and therefore will not be the ideal source for spectroscopy, where one would like to have a continuously tunable laser source in order to scan across a series of vibration-rotation transitions of the molecular gas to be investigated. Although we can make use of it for very special situations e.g.for the spectroscopy of paramagnetic molecules, where Zeeman-tuning of the molecular transition can be achieved, we must use other types of gain media for a tunable infrared laser. 

II. INFRARED SPECTROSCOPY OF MOLECULAR IONS USING FREQUENCY TUNABLE LASER SOURCES... 

Also advantageous to us is the generality of CARS spectroscc. Since it is based on the.Raman effect, CARS can be used for spectroscopic detection of any molecule. Also, as a Raman technique, CARS spectroscopy can be carried out in the visible region of the optical >ectrum, for which reliable, powerful, continuously tunable laser sources are cottimercially available. 

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