Confocal Raman spectrometer

Everall et al. [49] were interested in obtaining a simple, rapid method for determining the density of PET films and pellets. Although Raman spectroscopy had been shown to correlate with density, they found that the existing correlations were only valid when the samples consisted either only of unoriented samples or only of oriented samples, not when a combination of both types were present. They used a chemometrics approach to obtain a good correlation with density. Using four factors associated with the 1730-, 1096-, 996-, and 860-cm bands, they were able to predict the density of polymer pellets or chips and oriented films with a standard error of prediction of 0.0023 g/cm. Everall et al. [50] used a variation of this technique coupled to a confocal Raman spectrometer to... 

Raman spectra were recorded using a Lab Ram I confocal Raman spectrometer (Dilor, France). A He—Ne laser with a laser power of approximately 15 mW at the sample surface was used to provide an excitafion wavelength of 632.8 nm. A holographic notch filter reflected the exciting line into an Olympus BX40 microscope (Tokyo, Japan). 

W. Schabel, I. Ludwig and M. Kind, Measurements of concentration profiles in polymeric solvent coatings by means of an inverse confocal micro Raman spectrometer - Initial results. Drying Technol., 22, 285-294 (2004). 

Raman microspectroscopy results from coupling of an optical microscope to a Raman spectrometer. The high spatial resolution of the confocal Raman microspectrometry allows the characterization of the structure of food sample at a micrometer scale. The principle of this imaging technique is based on specific vibration bands as markers of Raman technique, which permit the reconstruction of spectral images by surface scanning on an area. 

While commercial Raman spectrometers collect the scattered light from a laser spot of size 1 pm at best and the Raman spectra also include information of sample regions above and below the focal plane, the implementation of confocal microscopy can improve the optical resolution and the depth of sharpness. The method leads to better image definition. Confocal microscopy means point illumination and that a small aperture is placed in the optical path so that only the scattered light located in a thin focus plane can reach the detector. The aperture-dependent spatial... 

This method is based on measuring the shift of the optical energy levels of fluorescent elements such as Cr3+ in response to a change of the stress state. This results in undergo as the result of altering the distance of ions within the strained crystal structure of the host lattice (Yu and Clarke, 2002). Equipment used to record photoluminescence spectra include confocal laser-Raman spectrometers equipped with a liquid nitrogen cooled CCD detector and a motorised X-Y microscope table to allow point-by-point mapping. 

There are several common configurations for Raman spectrometers. Unlike NIR, Raman can be readily done under a confocal microscope. Confocal Raman spectroscopy allows for the chemical composition of materials to be determined with micron spatial resolution including some depth profiling. Confocal Raman measurements have been shown to be useful quantitative analytical tools for the investigation of drug eluting stents [11]. Raman microscopy has been used to quantify thin... 

The test equipment of crystal type of gas hydrates consists of a laser Raman spectrometer, gas supply system, jacketed cooling type high-pressure visual cell, temperature control system, data acquisition and other parts. The experiment using a laser Raman spectrometer for the JY Co. in French produced Lab RAM HR-800 type visible confocal Raman microscope spectrometer. Laboratory independently designed a cooled jacket visible in situ high-pressure reactor, reactor with sapphire window to ensure full transparency of laser, and high pressure performance, visual reactor effective volume 3 ml, compression 20 MPa effective volume, to achieve characteristics of gas hydrate non-destructive and accurate measurement. The schematic representation of equipment is shown in Eigure 1. 

Silver deposition is an example of a metal deposition, which can be monitored by Raman spectroscopy. A Raman spectrometer is now usually a Raman microscope using confocal... 

Figure 7.27 Confocal Raman microscope spectrometer. The sample is illuminated by a laser light reflected on a dielectric mirror (DM) combined with a highly selective Notch filter. The Raman signals scattered from the sample are detected by highly selective avalanche photo diodes (APD) or via a monochromator on a CCD detector. The sample is scanned in two or three dimensions and the...

The incorporation of high-resolution optics in a Raman spectrometer allows sampling from areas of less than 1 x 10 m in diameter. The addition of a confocal microscope improves the axial resolution to a couple of microns. Those developments, along with the introduction of notch filters and holographic transmission gratings, allow the reduction of the acquisition time of Raman spectra from minutes to seconds. The fast data collection combined with the high lateral and vertical resolutions makes possible the collection of Raman images with several micron spatial resolutions. 

A confocal Raman microscope has been used to analyze the effect of stress on the diamond window for a loaded cell. The effect of simple stress fields on the Raman spectra on crystals of the same structure as diamond is well understood [22]. A series of scans were performed going down the axis of an anvil cell from the back face to the culet. The spectra from the scans when the DAC was loaded to 68 kbar, with the spectrometer polarization perpendicular to the laser polarization, are shown in Fig. 22. The spectra from the parallel... 

Table 5.50 lists the main features of Raman microspectroscopy. Virtually any object which can be observed under a microscope can be analysed with Raman microscopy. Here, the usual constraints inherent in electron beam methods (vacuum, metallisation, etc.) are totally absent. Although micro-Raman spectrometers mainly use visible excitation, the confocal configuration almost eliminates fluorescence which falls outside of the focal volume. The focus area for visible lasers is <1 /xm, whereas the focus diameter for NIR lasers is 20 fim. 

In principle, Raman microspectroscopy is attractive because the practical diffraction limit is on the order of the excitation wavelength, which is about 10-fold smaller for Raman spectroscopy with a visible laser than for mid-IR spectroscopy. It is therefore possible to focus visible laser light to much smaller spot sizes (400 nm in air and 240 nm with an oil immersion objective) than may be examined by mid-IR radiation. For various instrument-based reasons [4], charge-coupled device (CCD) Raman spectrometers have in practice proved to be far more successful for Raman microspectroscopy than ET-Raman spectrometers, and most instruments are based on this former concept. One further important instrumental advantage of the microscopes used for Raman microspectroscopy is their confocal design [5]. As the out-of-focus rays from an illuminated volume... 

Figure 2. Diagram of a confocal Raman detection system. A Helium-Neon laser is focused onto a sample through a microscope objective. Raman signals are epi-detected and sent to either an avalanche photodiode detector (APD) for imaging or dispersed onto a CCD camera in the spectrometer.

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