Bands filter rejection

Figure 9.12. FT-Raman spectrum of solid sulfur, obtained with a Bruker 66 FTIR and Raman attachment. Filter rejection band blocks Raman shifts from -f-55 to —130 cm. Small feature at zero shift is the residual elastic scatter transmitted by the rejection filter.

Band pass filters are generally characterised by a region of possibly high transmission, limited on either side of the spectrum by regions of rejection. Depending on the width of the transmission region, one may distinguish between narrow-band and broad-band filters. 

Fig. 4.57. Example of sensitive Raman equipment. The band pass filter, BP, cleans the laser radiation. The high NA objective lens LI focuses the laser on the sample and collects the Raman scattered radiation within a large solid angle. The band-rejection filter, BR, blocks elasti-...

Note about infrared radiation (IR) filters In the bolometer just described, the optimum conductance to the heat sink is G 2 x 10-10 W/K. This means that an absorbed power of the order of 1(T10 W saturates the bolometer. Since the bolometer is a broad-band detector, it would receive, e.g., a power of the order of 10 7 W from a 30 K black body. Of course, optical filtering is needed to reduce the bandwidth of the impinging radiation. Filtering takes usually place in several steps a room temperature filter eliminates visible light an intermediate temperature filter (at about 77 K) rejects the micron wavelengths, whereas the submillimetre or millimetre filter is made up of a low-pass and an interference band-pass filter. 

Figure 3. Transient absorption spectrum of a 2 x 10 M solution i in butyronitrile at 100 ps following a 0.3 mJ, 0.5 ps, 600 nm laser flash. Filters that reject stray excitation light cut out the 580-620 nm wavelength region, while the sharp cutoff at 440 nm is due to the intense absorption of the porphyrin Soret band at 419 nm.

As to the rejection of charging and interfacial current contributions, Rosamilia and Miller [71, 72] were able to extend the scan rate this required also to increase the modulation frequency but ensuring always p< 1. Also the determination of / involves one band passfilter, one RC filter, and a full wave rectifier which leads to a lag in the 17 /E curve relative to that of the corresponding I/E curve. 

Figure 15.5 Schematic of instrumental apparatus. The DT/MH-functionalized AgFON was surgically implanted into a rat with an optical window and integrated into a conventional laboratory Raman spectroscopy system. The Raman spectroscopy system consists of a Ti sapphire laser (Acx = 785 nm), band-pass filter, beam-steering optics, collection optics, and a long-pass filterto reject Raleigh scattered light. All of the optics fit on a 4 ft x 10 ft optical table.

Figure 1.2. Raman spectrum of room-temperature chloroform obtained with 514.5 nm light. Rayleigh scattering at zero Raman shift is heavily attenuated by a band reject filter and is actually several orders of magnitude more intense than the Raman scattering. The x axis is shown in three different scales but is normally plotted as Raman shift in reciprocal centimeters relative to the laser frequency (19,435 cm in this case). Although the Stokes Raman to the right is actually a negative frequency shift, convention assigns Stokes Raman shifts as positive numbers.

A third type of absorption filter useful for laser rejection is based on a semiconductor with a band gap slighdy lower in energy than the laser photons (18). Scattered laser photons are strongly absorbed by the semiconductor, while... 

Figure 9.1. Schematic of Raman spectrometer based on an acousto-optic tunable filter (AOTF). BP, bandpass filter BR, band reject filters APD, avalanche photodiode. (Adapted from Reference 9, with permission.)...

Figure 12.3. General schematic of fiber-optic Raman sampling, showing the laser-fiber interface and the fiber-spectrometer interface. The bandpass (BP) and band reject (BR) filters are sometimes integrated into the probe head. The fiber-optic (FO) length can vary over a wide range, from less than 1 m to greater than 100 m, depending on the application.

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