Single beam optical system

List the components of a single-beam optical system for absorption spectroscopy. List the components of single-beam optical system for emission spectroscopy. 

The infrared probe uses ATR to obtain the absorption information. The probe crystal is made from a chemically inert material, such as germanium or synthetic sapphire. The reflecting surfaces are masked so that the same area is covered by a sample each time an analysis is made. A single-beam optic system is employed, chopped at 45 Hz. Since the air path is less than 5 cm, as opposed to well over 1 m in conventional infrared spectrophotometers, absorption due to atmospheric water vapor and carbon dioxide is insignificant,... 

Early UV-Vis and IR spectrophotometers, back in the 1950s, were big clunkers that usually had double-beam monochrometers to compensate for opti-cal drift and electronic noise They were slow and only moderately sensitive. Improvements in optical and electronic technology have reduced the necessity for double-beam optical systems that reduce, the energy of the transmitted beam. Modem single-beam instruments are smaller faster, more sensitive, and more economical than the older versions. But double-beam instruments still provide the optimal stability and the choice depends on your need. All modem dispersive IR instmments are single beam. 

Spectrometers are instruments that provide information about the intensity of light absorbed or transmitted as a function of wavelength. Both single-beam and double-beam optical systems (see the schanatics in Chapter 2) are used in molecular absorption spectroscopy. Single-beam systems... 

An x-ray area detector can be used to collect the intensities of many reflections at a time. The crystal must be oriented in many different settings with respect to the incident beam but the detector needs to be positioned at only a few positions to collect all of the data. A charge coupled device (CCD) is used as the area detector on the Siemens SMART single crystal diffractometer system. The SMART detector consists of a flat 6-cm circular phosphorescent screen that converts x-ray photons to visible light photons. The screen is coupled to a tapered fiber optics bundle which is then coupled to a one inch by one inch square CCD chip. The CCD chip has 1024 x 1024 pixels each of which stores an electrical charge proportional to the number of... 

Double-beam AA spectrophotometers are still marketed by instrument manufacturers. A double-beam system compensates for changes in lamp intensity and may require less frequent re-zeroing than a single-beam instrument. These considerations had more merit some years ago when hollow cathode lamps suffered from some instability. It should be noted, however, that the optical... 

To obtain a quantitative measure of the CL intensity of individual CL emissions, an optical multichannel analyzer was coupled to the optical system of an electron microprobe allowing simultaneous collection of CL spectra and minor element data from a single point (Steele, I.M. Meteoritics. submitted). For CL spectra obtained with a 15 kV focused beam, enstatite from both enstatite chondrites and achondrites showed three distinct peaks (Fig.l) centered at about 742, 664, and 483nm. To allow assignment of these peaks, spectra from synthetic Mn and Cr doped enstatite are shown in Fig. 2 and the emissions from these two samples closely match the two red peaks of meteoritic enstatite neither synthetic sample shows a blue peak. The peak positions of Cr and Mn are not constant for different meteoritic enstatites and are not the same as for the Cr and Mn doped standards. The variation is about 20nm... 

It would be logical to arrange the components so far described in a straight line optically, and indeed this is done in the most successful instruments producing the so-called single beam system represented in Fig. 11. 

---