Optical pathlength

Detection UV absorbance detection is typically used for capillary electrophoresis. However, the short optical pathlength of the capillary results in poor detection limits... 

M. Hiraoka, M. Firbank, M. Essenpreis, M. Cope, S. R. Arridge, P. van der Zee, and D. T. Delpy. A monte carlo investigation of optical pathlength in inhomogeneous tissue and its application to near-infrared spectroscopy. Physics in Medicine and Biology, 38 1859-1876, 1993. 

In layers with very small optical pathlengths (Sd < 1) the forward and backward fluorescences are equally intense like in nonscattering media. However, with increasinglayerthickness, Ff grows slowerthan Fb, passes through a maximum, and decreases... 

The log-baseio attenuance (or absorbance) (i.e., D ox A) divided by the optical pathlength (/). This coefficient, symbolized by a, is thus equal to / log(Po/P). See Beer-Lambert Law Absorbance Molar Absorption Coefficient Absorption Spectroscopy... 

With this spectrometer, a difference mid-IR spectrum at a selected time after sample excitation is recorded by sweeping from 1640 to 940 cm in steps that may be as short as approximately equal to the spectral resolution of the spectrometer—in this case, 8 cm. The sample solution is pumped through a flow cell that has IR-transmitting Cap2 windows set with a 0.1-mm optical pathlength. The Bap2 windows have also been used for the sample cell. ... 

The amount of light absorbed is a function of the so-called absorption coefficient (A ) and of the optical pathlength in the atomiser cell (ft) k depends on the frequency of the selected analytical line and on the concentration of the analyte absorbing atoms. The general absorbance law (Lambert Beer Bouguer law) relates transmittance (and so measured intensities I and If) to k and b through the following equation ... 

A test for the sensitivity of a fluorimeter is to measure the intensity of fluorescence of the Raman diffusion peak of a cell filled with water and with an optical pathlength of 1 cm. If the wavelength of excitation is regulated to 250 nm, at which wavelength must the measurement be made (the Raman displacement of water is 3 380 cm-1) ... 

Emissive spectral features were consistent with those previously reported for CdS Te (6-13) and confirmed (Roessler s correlation, (12)) that the Te concentration was <100 ppm. TheA,5x5xl mm samples had resistivities of A,2 ohm-cm (four point probe method) and were oriented with the 5x5 mm face perpendicular to the c-axis. Samples were first etched with 1 10 (v/v) Br2/MeOH and then placed in an ultrasonic cleaner to remove residual Br2. The electrolyte was either sulfide, 1M 0H /1M S2-, or polyselenide, typically 5M 0H /0.1M Se2 /0.001M Se22- short optical pathlengths (<0.1 cm) were used to make the latter essentially transparent for A >500 nm. Electrode and electrolyte preparation as well as electrochemical and optical instrumentation employed have been described previously (8). Electrolytes were magnetically stirred and blanketed under N2 during use. 

A vernier adjustment (scale expansion) between fixed ranges is also available for calibration of absorbance and transmittance. The dual flow cells have a capacity of 8 /il and a 10-mm optical pathlength. 

Figure 1. IR spectrum of CpMn(CO)3 (ca. 10 3M) dissolved in scXe (1100 psi) at ambient temperature, obtained with an optical pathlength of 1.8mm. The unique spectroscopic transparency of scXe reveals approximately 50 bands associated with CpMn(CO)3 in the region 4500 -1000 cm 1. The region below 1000 cm 1 is cut off by the CaF2 window material employed in our cell.

Figure 3. IR band due to v(H-H) vibration of T 2-H2 in W(CO)5(H2). The spectrum was recorded at ambient temperature with a total pressure (H2 + scXe) of 3000psi and a 1.8 mm optical pathlength. Under these conditions, W(CO)5(H2) has a lifetime of approximately 3 min. The spectrum was recorded whilst the sample was being irradiated with UV light.

The physical description of the Bragg diffraction regime is similar to the case of X-ray diffraction in a crystal lattice (Figure 3.18). The diffracted beam is extensively re-diffracted inside the crystal due to its thick optical pathlength, and the diffraction takes place at a... 

Attenuated total internal reflection (ATR) probes offer several advantages over other probe types. ATR is a phenomenon that relies on a difference in the index of refraction of a crystal and that of the solution with which it is in contact to prevent light from escaping the crystal. Only the evanescent wave of the light interacts with the solution layer at the crystal face. The result is an optical pathlength of only a few microns. Typical designs make use of faceted crystals or hemispheres (see Figure 6.1). The most common ATR material in the UV-vis is sapphire. In rare cases, fused silica may be used. ATR allows spectra to be taken of neat samples with optical density (OD) of 500-1000... 

The extruders were monitored using a pair of custom-made transmission probes inserted into the extruder die just downstream from the screws. Each probe consisted of a sapphire window brazed into a metal body a quartz rod behind the window piped the light to the end of the probe low-OH silica fiber-optic bundles connected the probe to the NIR analyzer, an LT Quantum 12001. Optical pathlengths were typically between 0.3 and 2.0 cm. 

Applied fields change the optical pathlength Phase modulators... 

Spectroelectrochemical experiments can be used to probe various adsorption and desorption processes. In particular, changes in the absorbance accrue from such processes can be probed utilizing the large ratio of surface area to solution volume of OTEs with long optical pathlength (30). Additional information on such processes can be attained from the Raman spectroelectrochemical experiments described below. 

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