Optical filter emission filters

Until the advent of lasers the most intense monochromatic sources available were atomic emission sources from which an intense, discrete line in the visible or near-ultraviolet region was isolated by optical filtering if necessary. The most often used source of this kind was the mercury discharge lamp operating at the vapour pressure of mercury. Three of the most intense lines are at 253.7 nm (near-ultraviolet), 404.7 nm and 435.7 nm (both in the visible region). Although the line width is typically small the narrowest has a width of about 0.2 cm, which places a limit on the resolution which can be achieved. 

Figure 2 Comparison of NO + 03 and NO + O chemiluminescence spectra with blue and red optical filter transmissions and the response of a blue-sensitive photomultiplier tube. Note the blue shift of the NO reaction with O compared to that with 03 and that the addition of a blue filter effectively removes emission from NO + 03, while the red filter effectively removes emission from NO + O.

In addition to the ability to react nonspecifically with hydrocarbons, active nitrogen can readily participate in energy transfer reactions with volatile organometal-lic compounds, leading to atomic emission from the metal atom. By use of appropriate optical filters, selective detection of elements such as aluminum, lead, tin, and mercury has been achieved in the presence of large excesses of organics [58],... 

Moreover, it is easy to show that, if the emission is observed without a polarizer, an excitation polarizer must be set at 0 = 35.3° (cos2 6 = 2/3). This arrangement is suitable when the fluorescence is detected through an optical filter (to reject scattering light) and not through a monochromator, because of the polarization dependence of the transmission efficiency of the latter. 

A variety of optical alignment accessories for the launch of the excitation light into the fiber optic temperature probe, the collection of the fluorescence response, and optical filters used to isolate the excitation and fluorescence emission at the detector and in some cases at the excitation source as well. 

The detection performance of an LIF photometric device is governed by the emission filter(s), excitation filter(s), detector type, the excitation source and the detection scheme. The selection of optical elements and device configuration as it relates to the detection performance is further described by expanding the collection efficiency term in Equation 11.3 ... 

The flame photometry detector is specific for compounds containing sulphur or phosphorous. Compounds eluting from the column are burned in a flame hot enough to excite these elements and induce photonic emission, which is detected by a photomultiplier (see Fig. 2.12). Optical filters are used in the detection system to... 

Up-conversion. This is similar to autocorrelation, but the laser pulse is mixed with the luminescence light of a sample in an SHG crystal to generate light of frequency vL + vE. The time between the laser pulse (vL) and the luminescence emission (vE) is varied by means of an optical delay path, and the light of added frequency is detected by a usual PM tube via optical filters. 

Fig. 7 Set-up for time-resolved imaging of 96-microwell plate formats, a Fast gateable CCD-camera, b Optical emission filter, c Light-guiding adapter, consisting of 96 optical fibers, d 96-microwell plate (black with transparent bottom), e Optical excitation filter, f Pulseable LED array with 96 light emitting diodes...

An oxygen sensor array using these principles was developed by Liebsch et al. [60]. A modification of the applied imaging set up is illustrated in Fig. 7. It consists of a CCD camera with a fast mechanical shutter, an array of 96 pulsed LEDs, a computer-steered pulse generator, a constant power supply, a light-guiding adapter with 96 optical fibers, and the corresponding excitation and emission filters. 

In order to integrate the optics in the microchip for fluorescent detection (see Figure 7.7), describe how a bandpass emission filter is fabricated. (2 marks)... 

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