Charge transfer device (CTD) detectors consist of two closely related silicon integrated circuits: the charge-coupled device (CCD), invented in 1970, and the charge injection device (CID), invented in 1973. Initially, several applications were proposed for these integrated circuits, including use as shift registers, logic and memory devices, electronic delay lines, and imaging detectors. The last application has so dominated the design and use of CTDs that they are among the most common electronic imaging detectors manufactured today.

Applications of Charge Transfer Devices in Spectroscopy

Spontaneous Raman scattering from adsorbates on surfaces is a powerful vibrational spectroscopy technique that is due to the very large frequency range and high resolution currently possible with visible lasers and spectrometers. Because of the extremely low Raman cross sections of nonresonant molecules, one must use either some sort of signal-enhancement technique or long integrations using multichannel detection in order to have monolayer sensitivity. We have used a backthinned, unintensified, liquid-nitrogen-cooled charge-coupled device (CCD) detector to obtain high-quality multichannel unenhanced Raman scattering spectra from organic monolayers on surfaces. This system has roughly a factor-of-10 greater sensitivity for very low-light-level visible excitation Raman spectra than intensified multichannel detectors currently on the market. A description of our detection system is given along with a comparison with other commercially available multichannel detectors suitable for low-light-level visible Raman spectroscopy. We discuss the advantages and disadvantages of using CCD’s, the special problems that one encounters in their use as Raman detectors, and our methods for overcoming these problems. Prospects for the future use of CCD’s for low-light-level Raman spectroscopy will also be discussed.

Use of an unintensified charge-coupled device detector for low-light-level Raman spectroscopy

Laser speckle based digital optical methods in structural mechanics: A review

The development of a computer-aided rapid-scanning detector for HPLC based on the linear photodiode array UV-visible spectrophotometer is described. Chomatograms monitored at up to three wavelengths, with automatic capture of spectra for eluted peaks and post-run processing of spectral data to generate log10 (A) spectra, second derivative and fourth derivative spectra, are described. Methods are reported for the analysis of forensic samples of diacetylmorphine (heroin) in the presence of the degradation products and potential contaminants caffeine, papaverine, 6-acetylcodeine, thebaine, 6-acetyl-morphine, procaine and morphine separated by HPLC. The novel use of second and higher derivative spectra for the qualitative characterisation of drugs and contaminants separated by HPLC is described.

Computer-aided multichannel detection in high-performance liquid chromatography

The analytical utility of fluorescence spectrometry of polycyclic aromatic hydrocarbons matrix isolated in vapor-deposited, annealed n-heptane deposits is considered. Much greater spectral resolution can be obtained in heptane than in conventional (nitrogen or argon) matrices; the possibilities for selective excitation in alkane matrices of fluorescence of individual compounds in multicomponent samples can be exploited effectively only if dye-laser excitation is utilized. In contrast, laser excitation offers few general advantages over lamp excitation for matrix-isolation fluorometry in conventional matrices. The quantitative aspects (linear dynamic range, precision, applicability to mixtures) of matrix-isolation fluorometry in n-alkane media also are discussed. 6 figures.

Laser-induced fluorescence spectrometry of polycyclic aromatic hydrocarbons isolated in vapor-deposited n-alkane matrices

Recently there has been a great deal of interest in the use of solid-state multichannel detectors as sensors for rapid-scan spectroscopy. The charge-coupled device (CCD) photoarray, not previously characterized for this application, is described. The unit has 1728 elements, arranged linearily, which integrate light over the same time frame; the photo signals are then read serially. The CCD was found to produce signals which are linear with both intensity and integration time. The dark signal at −10°C is 0.1% of saturation for a 10 ms integration time, and the noise level is less than 0.08% of saturation. The wavelength response is in the visible region. The application for rapid-scan spectrophotometry is also discussed.

Steven L. Paul

Papers

Characterization of a Charge-coupled Device Photoarray as a Molecular Absorption Spectrophotometric Detector