Lasers spectral range

A Raman microscope (Renishaw, 785-nm laser, spectral range 800-100cm ) with a line-mapping detector (21 pixels/line) was used to analyze a solid dosage form. The image size was 105 x 88 pixels, that is, 325 pm x 270 pm, and acquisition time was about 40 min. Spectra were smoothed and normalized. Peak heights were determined for the three main compounds—API, lactose, and cellulose (Figure 11)—in order to create distribution maps. 

Modern commercial lasers can produce intense beams of monochromatic, coherent radiation. The whole of the UV/visible/IR spectral range is accessible by suitable choice of laser. In mass spectrometry, this light can be used to cause ablation, direct ionization, and indirect ionization (MALDI). Ablation (often together with a secondary ionization mode) and MALDI are particularly important for examining complex, intractable solids and large polar biomolecules, respectively. 

The materials discussed yield lasers operating ia the infrared and near visible spectral ranges. Many appHcations of lasers, such as printing or high density memories, requite as short a wavelength as possible. The III—V system most suitable for short wavelength visible operation is the (Al Ga Q In ... 

SFG [4.309, 4.310] uses visible and infrared lasers for generation of their sum frequency. Tuning the infrared laser in a certain spectral range enables monitoring of molecular vibrations of adsorbed molecules with surface selectivity. SFG includes the capabilities of SHG and can, in addition, be used to identify molecules and their structure on the surface by analyzing the vibration modes. It has been used to observe surfactants at liquid surfaces and interfaces and the ordering of interfacial... 

Since the vibrational spectra of sulfur allotropes are characteristic for their molecular and crystalline structure, vibrational spectroscopy has become a valuable tool in structural studies besides X-ray diffraction techniques. In particular, Raman spectroscopy on sulfur samples at high pressures is much easier to perform than IR spectroscopical studies due to technical demands (e.g., throughput of the IR beam, spectral range in the far-infrared). On the other hand, application of laser radiation for exciting the Raman spectrum may cause photo-induced structural changes. High-pressure phase transitions and structures of elemental sulfur at high pressures were already discussed in [1]. 

Here Q(t) denotes the heat input per unit volume accumulated up to time t, Cp is the specific heat per unit mass at constant pressure, Cv the specific heat per unit mass at constant volume, c is the sound velocity, oCp the coefficient of isobaric thermal expansion, and pg the equilibrium density. (4) The heat input Q(t) is the laser energy released by the absorbing molecule per unit volume. If the excitation is in the visible spectral range, the evolution of Q(t) follows the rhythm of the different chemically driven relaxation processes through which energy is... 

A major technological innovation that opens up the possibility of novel experiments is the availability of reliable solid state (e.g., TiSapphire) lasers which provide ultra short pulses over much of the spectral range which is of chemical interest. [6] This brings about the practical possibility of exciting molecules in a time interval which is short compared to a vibrational period. The result is the creation of an electronically excited molecule where the nuclei are confined to the, typically quite localized, Franck-Condon region. Such a state is non-stationary and will evolve in time. This is unlike the more familiar continuous-wave (cw) excitation, which creates a stationary but delocalized state. The time evolution of a state prepared by ultra fast excitation can be experimentally demonstrated, [5,7,16] and Fig. 12.2 shows the prin-... 

Laser radiation can be obtained nowadays over a wide spectral range from the ultraviolet to the far infrared region, covering the range of optical spectroscopy. Fignre 2.4 shows schematically the spectral zones covered by different types of lasers. Although there are some specific regions in which direct laser action is not available. 

On the one hand, the output wavelength of a dye laser can be continuously varied within their broad emission band (various tens of nanometers). Therefore, with different dyes the overall spectral range covered by these lasers can be extended from around 400 nm to 1.1 jim, as shown in Figure 2.12. 

Figure 2.15 The spectral range of laser emission for several semiconductor materials.

Figure 2.18 The spectral range covered by different tunable solid state lasers based on transition metal ions.

Let us now devote our attention to one of the most popular lasers in the field of optical spectroscopy the Ti-sapphire laser. As shown in Figure 2.18, the spectral range covered by this laser is the largest among the various tunable solid state lasers from 675 nm up to 1100 nm. In this laser, the active medium is formed by optically active Ti + ions in the AI2O3 crystal host. 

Figure 2.20 The spectral range covered by the fundamental radiation of a Ti-sapphrre laser and the various harmonic generation processes second, third, and fourth harmonic generation (SHG, THG, and FHG, respectively) (courtesy of Quantronix).

Therefore, it is clear that different frequency conversion processes, together with the variety of lasers, have led to a great variety of coherent sources with large and differing tuning ranges. The whole spectral range of 185-3400 nm can be covered by different methods. 

The optical features of a center depend on the type of dopant, as well as on the lattice in which it is incorporated. For instance, Cr + ions in AI2O3 crystals (the ruby laser) lead to sharp emission lines at 694.3 nm and 692.8 nm. However, the incorporation of the same ions into BeAl204 (the alexandrite laser) produces a broad emission band centered around 700 nm, which is used to generate tunable laser radiation in a broad red-infrared spectral range. 

The Yb + ion is commonly used to make solid state laser crystals. In which spectral range do you expect these lasers to emit ... 

For comparison the output power of a high-pressure mercury lamp (Osram HBO 200) also is listed. The reader has to consider, however, that the mercury lamp radiates this power into the unit solid angle (= 60°) distributed over the spectral range from 2000 to 6000.A, whereas the laser intensity is concentrated at a single wavelength and collimated in a beam with a very small divergence between 10 and 10" sterad. 

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