Spectral transmission

For prism spectrometers, the spectral transmission depends on the material of the prism and the lenses. Using fused quartz the accessible spectral range spans from about 180 to 3000 nm. Below 180 nm (vacuum-ultraviolet region) the whole spectrograph has to be evacuated, and lithium fluoride or calcium fluoride has to be used for the prism and the lenses, although most VUV spectrometers are equipped with reflection gratings and mirrors. 

In the infrared region, several materials (for example, CaFj NaCl, and KBr crystals) are transparent up to 30 /rm (Fig.4.6). However, because of the high reflectivity of metallic, coated mirrors and gratings in the infrared region, grating spectrometers with mirrors are preferred rather than prism spectrographs. 

Many vibrational-rotational transitions of molecules such as H2O or CO2 fall within the range 3fl0 /tm causing selective absorption of the transmitted radiation. Infrared spectrometers therefore have to be either evacuated or filled with dry nitrogen. Because dispersion and absorption are closely related, prism materials with low absorption losses also show low dispersion, resulting in a limited resolving power (see below). 

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Transmission. The spectral transmission of glass is determiaed by reflectioa at the glass surfaces and the optical absorption within the glass. Overall transmission of a flat sample at a particular wavelength is equal to (1 — R), where P is the absorption coefficient, t the thickness of glass, and... 

Pure carbon disulfide is a clear, colorless Hquid with a deHcate etherHke odor. A faint yellow color slowly develops upon exposure to sunlight. Low-grade commercial carbon disulfide may display some color and may have a strong, foul odor because of sulfurous impurities. Carbon disulfide is slightly miscible with water, but it is a good solvent for many organic compounds. Thermodynamic constants (1), vapor pressure (1,2), spectral transmission (3,4), and other properties (1,2,5—7) of carbon disulfide have been deterrnined. Principal properties are Hsted in Table 1. 

An important effect of air pollution on the atmosphere is change in spectral transmission. The spectral regions of greatest concern are the ultraviolet and the visible. Changes in ultraviolet radiation have demonstrable adverse effects e.g., a decrease in the stratospheric ozone layer permits harmful UV radiation to penetrate to the surface of the earth. Excessive exposure to UV radiation results in increases in skin cancer and cataracts. The worldwide effort to reduce the release of stratospheric ozone-depleting chemicals such as chlorofluorocarbons is directed toward reducing this increased risk of skin cancer and cataracts for future generations. 

Figure 5. Spectral transmission of several kinds of materials.

A hollow waveguide (HWG) is essentially a hollow tube that transports light from one end to the other either by multiple mirror reflection or by total internal reflection. The hollow structure gives them several advantages (i) a high power threshold, (ii) low insertion losses, (iii) no end reflections, (iv) a small beam divergence, (v) robustness and - especially important for sensor applications - (vi) a wide spectral transmission range. 

In this chapter, the motivations to adopt MLR systems for optical e-beam, x-ray, and ion-beam lithographic systems will be given, followed by a survey of published MLR systems. Specific practical considerations such as planarization, pinhole and additive defects, interfacial layer, etch residue, film stress, interference effects, spectral transmission, inspection and resist stripping will be discussed. The MLR systems will be compared in terms of resolution, aspect ratio, sensitivity, process complexity and cost. 

Figure 21. Spectral transmission of a 100-nm layer of hydrogenated amorphous Si deposited by plasma CVD of a silanethelium mixture on a Suprasil quartz substrate. (Reproduced with permission from Ref. 53.)...

TF Systems A TF is a device whose spectral transmission can be controlled by applying a voltage or acoustic signal. There are two main TF devices acousto-optical TF (AOTF), based on diffraction, and liquid crystal TF (LCTF), based on birefringence. An AOTF is a transparent crystal in which an ultrasonic wave field is created,... 

The radiation may be due to emissions from a hot source, or to the luminescence, fluorescence or phosphorescence of the sample. An emission spectrum consists of a number of generally very narrow peaks (called spectral lines) occurring at certain wavelengths which are characteristic of the materials contained within the source. The amplitudes of the peaks are related to the abundance or concentration of the materials present. Alternatively, radiation from a source is passed through a sample. In this case the quantity absorbed by the sample at a particular wavelength is again characteristic of the materials present in the sample. This is termed absorption spectrometry and produces spectral transmission lines in the form of equally narrow valleys—or peaks (Fig. 6.42) where the information is expressed in terms of absorbance (si) rather than transmittance (20<57>, and ... 

The lack of spectral windows in the spectrum of the mobile phase, i.e., regions in the spectrum where the transmission is greater than 30%. This limits not only the choice of mobile phase but also the path length of the detector cell e.g., acetonitrile in a 1-mm cell has a spectral window of 6-8 /Am and 8.5-11 /Am, but with a 3-mm cell, both of these regions are spectrally opaque. Thus, the choice of path length is a compromise between spectral transmission and sensitivity. 

Thorpe, A., Douglas, R. H., and Truscott, R. J. W., Spectral transmission and short-wave absorbing pigments in the fish lens — I. Phylognetic distribution and identity, Vision Res., 33, 289, 1993. 

The actual spectral absorption generally observed in vision research is not the actual function for several reasons, some of which will be discussed in the next Section. However, a major reason, is related to the design of the experiment. The visual spectra of the individual chromophores of vision are relatively narrow. If an experiment is designed where the absorption spectrum is sampled using a finite width spectral filter, the measured spectrum is defined by the convolution of the actual spectral transmission function and the filter sampling function. The resulting mathematics can assume three forms. 

Some important deposition parameters to control ZnO Al film properties are deposition pressure, substrate temperature, and amount of oxygen in the sputter gas mixture (see e.g. [93,96,100,101]). Doping concentration in ZnO films plays another important role for opto-electronic properties [97,100,102]. Figure 8.13 shows the spectral transmission of films that were reactively sputtered from targets with different aluminum concentration at optimized conditions [93]. Sputter conditions and film properties are given in Table 8.2. 

Fig. 8.13. Spectral transmission of differently doped ZnO Al films. The films were prepared in an in-line system by reactive MF sputtering. The subscripts denote the aluminum concentration of the corresponding metallic targets in at. %. Deposition conditions and film properties are given in Table 8.2...

When radiation is incident on a translucent body, part of the incident radiation is reflected, part is absorbed, and the remainder is transmitted through the translucent body (Fig. 11.4). An example of a translucent body is a pane of glass. The relationship between the spectral reflectivity px, the spectral absorptivity ax and the spectral transmissivity Tx of the translucent body is... 

Fig. 2 Waveguide mode-surface plasmon coupling in fiber geometry with an area of removed cladding and a gold deposition therein, a) Experimental scheme for a single wavelength transmission experiment under controlled coupling angle a into the fiber, b) Experimental scheme for a spectral transmission experiment...

In the sensor developments of AuNPs on waveguides, the experimental technology is based on transmission experiments and in some cases for optical fibers on a transmission-reflection experiment. Nearly all groups detect the LSPR spectral position by laimching white light into a waveguide device and detect the spectral transmission dip, and its spectral shift due to a recognition event on the surface functionalization on the AuNPs (Fig. 5). 

Fig. 8 Experimental scheme of a spectral transmission experiment of a photonic crystal Bragg reflector micro-cavity fabricated out of refilled holes in silicon. The central refilled hole acts on a nanocavity. AuNPs are immobilized in and around the central nanocavity...

Fig. 9 Planar-waveguide photonic crystals by a periodic pattern of AuNPs on the waveguide surface, (a) Experimental scheme for a spectral transmission experiment under 0° geometry through the AuNP pattern and the waveguide stmcture. (b) Experimental scheme of a spectral transmission experiment applying waveguide modes...

Cemi used spectral transmission and extinction using UV, visible and near IR to measure slurry particle size distributions with undiluted continuous flow [347]. The method uses multiple linear detector array spectrometers. It also uses multiple sample cells of different optical depths optimized for a specific spectral range, multiple optical paths and multiple linear detector arrays. 

Figure 15 (A) Spectral transmission curves showing effect of glass type and thickness. (B) Transmittance curves of ampoules (61) and vials (62) used in original and subsequent Japanese photostability studies. (61) 20mL colorless ampoules (JIS R3512, No. 5), (62) 15mL colorless vials (N-16, Mamemu, Osaka). Source From Ref. 5.

The spectral transmissivity of low-iron glass at room temperature for different thicknesses. 

The variation of the spectral transmissivity of a 0.6-cm-thick glass window is as given in Fig. PI2-50. Determine the average transmissivity of this window for solar radiation (7 - 5800 K) and radiation coming from surfaces at room temperature (T 300 K). Also, determine the amount of solar radiation transmitted through the window for incident solar radiation of 650 W/m . 

The spectral transmissivity of a glass cover used in a solar collector is given as... 

Note that - I when no radiation is absorbed and thus radiation intensity remains constant. Also, the spectral transmissivity of a medium represents the fraction of radiation transmitted by the medium at a given wavelength. 

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