Sapphire Raman spectrum

As a result, cuvettes for Raman spectroscopy should be carefully selected. They may, due to their impurities, add a background to the spectrum of the sample. In addition, all cuvette materials produce their own Raman spectra, which have to be considered, when the Raman spectra of the sample are evaluated. Fig. 3.5-17 a shows a Raman spectrum of a typical optical glass BK7, Fig. 3.5-17 b that of quartz glass suprasil, and Fig. 3.5-17 c of sapphire. Suprasil is a synthetic quartz which does not normally contain impurities. Therefore, Suprasil of ESR quality is highly recommended as Raman cuvette material. Also, sapphire is a good cuvette material, as it is very hard, inert, has a good thermal conductance, and shows only weak but sharp Raman lines (Porto and Krishnan, 1967). It is used for the production of the universal Raman cell (Schrader, 1987). The sharp Raman lines of sapphire observed in the spectra of the sample may be subtracted from the spectrum or used as internal standard for quantitative analyses (Mattioli et al, 1991). 

Fig. 5.6 Hyper-Raman spectrum of Cgo microcrystals excited by 790-nm pulse radiation from the Ti-sapphire laser, with theoretically calculated hyper-Raman-active modes black bars) and Raman-active modes gray bars) [28]...

Figure 9.40 shows another example of residual strain effects on the Raman spectrum. The Si stretching vibration changes its frequency when Si is in the form of a thin film on sapphire. We can compare the Raman band positions between the strain-free sample and strained sample to evaluate the bond length change, which can be converted to residual strain. The residual strain is commonly elastic in nature. Thus, the residual stress in materials can be determined with the linear elastic relationship between strain and stress. 

Figure 14 shows the Raman spectrum of a rat stomach measured ex vivo using the hollow-fiber probe. A spectrum taken by using a Raman microscope is also shown for comparison. The excitation power was 29 mW, and the exposure time for the measurement was 60 s. Although Raman peaks of the sapphire-ball lens at 630... 

Oxidized silicon is the most commonly used substrate because it provides enhanced optical visibility of graphene (Section 4) and can be used for transport measurements. However, mechanically exfoliated graphene has also been deposited on other substrates such as quartz, silicon, glass, sapphire, NiFe, and GaAs [57, 58] no strong effects on the Raman spectrum have been observed by using these substrates. 

Figure 8 Raman spectrum of a pargasite inclusion in a sapphire from Kashmir. Note that the peaks with a P belong to the pargasite spectrum, whereas the peaks with a s belong to the...

Figure 9 Raman spectrum showing the different phases of a three-phase inclusion in sapphire from Madagascar. The labeled peaks are assigned to sapphire (top), diaspore (middle), and CO2 (bottom). 

Figure 7 Effect of window position on the observed optic background for an opaque latex sample. Raman spectra of latex obtained with (a) a X10 objective, (b) an immersion optic focused close to the window surface, and (c) an immersion optic focused into the sample, and (d) the Raman spectrum of the sapphire window 785-nm excitation. Note that bands marked with an asterisk originate from the sapphire window. 

As an example of this method, we present a simulation of this technique using experimentally realistic values (/). We assume that the laser source is an ultrabroadband titanium-sapphire laser producing transform-limited pulses of uniform power spectral density between 700-1000 nm. The bandwidth from 800-1000 nm is reserved for stimulating CARS, while the bandwidth from 700-800 nm is used as the reference pulse. In this simulation, we desire to simulate the measurement of the relative amounts of DNA (deoxyribonucleic acid) which has a resonance at 1094 cm" and RNA (ribonucleic acid) which has a resonance at 1101 cm A hypothetical Raman spectrum was created which has Lorentzian resonances at both frequencies. A pulse is designed such that... 

Figures 2.83 and 2.84 present spectra obtained with 2H-WS2 and IF-WS2 dispersed in PAO and subjected to a process of load and unload successively. The process of loading consists in recording the spectrum of the pristine product put on the ball, closing the contact and then applying loads from 1 to 10 N. The unloading corresponds to the opposite process. The diameter of the zone analysed inside the contact area is approximately of 5 am. After closing the contact, the appearance of a peak to 418 cm can be noticed. This peak is due to the sapphire flat and its intensity depends on focusing the beam during Raman spectrum acquisition. For the two samples, a displacement of this peak due to the pressure is observed, which shows an elastic deformation of sapphire during the test.

Information exists about the use of measuring cells made entirely of diamond or graphite with or without embedded diamond windows. Diamond cells were used, for instance, by Toth and Gilpatrick [333] in the investigation of the Nb(IV) spectrum in a LiF - BeF2 molten system at 550°C. Windowless graphite cells for the IR spectroscopy of melts were developed by Veneraky, Khlebnikov and Deshko [334]. Diamond, and in some cases windowless sapphire or graphite micro-cells, were also applied for Raman spectroscopy measurements of molten fluorides. 

Fig. 22. Low-frequency spectra of Mb obtained with Soret excitation (a) MbCO photo-lyzed with 20-30 psec pulses, (b) MbCO photolyzed with 10 nsec pulses of approximately 435 nm from the 10 Hz output of a Nd YAG laser system (average energy 1.0-1.5 mJ/ pulse), and (c) spectrum of deoxyMb taken under same conditions as in (b). Asterisks denote Raman lines of the sapphire cells used in the nanosecond experiments. (From Findsen et al. )...

Lasers can be classified as either continuous or pulsed sources, depending on whether their light output is steady or intermittent. This operational difference is dependent on the nature of the pump source, as a continuous excitation source will result in a continuous output beam, and a pulsed source yields a pulsed beam. Both have advantages for particular experiments. Continuous output is useful in Raman speetroseopy, for example, but pulsed lasers can be used in experiments involving short-lived speeies as deseribed in Section 2.8.1. Another operational difference is that some lasers are tunable, so they ean be used in a conventional way to scan a spectrum, whereas others are limited to a narrow frequency range. The titanium-doped sapphire laser is an example of a highly tunable infrared laser, commonly used in vibrational spectroscopy. The low-cost gas lasers tend to operate at a fixed frequency, but with superb resolution (<3 GHz), exactly what is needed for Raman spectroscopy. Semi-conductor (also known as diode) and... 

In our work we have used the positions of cyclohexane lines as the basis for this compensation because their Raman shifts are well known. In a system designed for routine operation, a stable solid Raman-active optical element in the sample beam would probably be used to produce this piece of information. For example, a sapphire window might be used between the probe head and sample to provide a single sharp line of known Raman shift in every sample spectrum. 

The primary tool is measurement of the Raman signal produced by a standard substance, perhaps sapphire or diamond, both of which have strong and simple spectra. The Raman shift is known and the wavelength is measured by the procedure that is described earlier. One aspect of the compensation routine is to include a measurement of the Raman-shift standard in the system self-test that is run at the start of each measurement session under the conditions that will obtain when samples are being run. A Raman-inactive substance that scatters is used as a sample. This produces a strong shift standard spectrum that permits unambiguous identification of the position of its signal. Its intensity provides an observation of the condition of the laser. 

Figure 5 Raman spectra obtained from three of the four common window materials (a) fused silica, (b) quartz, and (c) diamond. Note that the spectrum of the fourth popular window, sapphire, is shown in Fig. 7.

To highlight the Raman signal due to pure WS2, the spectrum of the sapphire flat was withdrawn from the experimental spectrum. The spectra obtained are very similar to the spectrum... 

---