Application of a Wave-Length Modulation Device to Problems concerning Spectrometer Misalignment

Abstract

The use of wave-length modulation as a tool for minimizing spectrometer spectral misalignment is examined. A vibrating quartz plate is employed to repetitively scan a small wave-length interval at the exit slit of a spectrometer. Increased latitude is thereby provided for any slit or wave-length misalignment of the spectrometer, as long as the correct signal detection system is employed. Investigation of the effects of wave-length modulation on a typical line spectrum has revealed signal averaging as the optimum detection system for this approach. From this, additional approaches are suggested for manual and automatic routine correction of spectrometer wave-length drift using existing optical systems. Also, a new technique is suggested for automatic feedback correction of the spectrometer using an on-line digital computer. Methods of implementation of all these procedures are considered and discussed.

Inexpensive, wavelength-modulated filter flame photometer

“…Refers to the bandpass of the interference filter (Narrow = 13 Á, Broad = 100 A). lyte line, the modulation pattern of the interfering line will differ from that of the analyte and can therefore be discriminated on the basis of phase or frequency (9). For example, a repetitive wavelength scan which is centered over the analyte line will produce an evenly spaced train of detected analyte peaks but would generate a slightly asymmetrical progression of interferant peaks.…”

“…In wavelength modulation, the wavelength under observation by the photodetector is repetitively scanned at a predetermined frequency. In recent years, this technique has been employed in flame spectrometry to enable the use of continuum sources in atomic absorption (2-5), to reduce broad-band spectral interferences in flame spectrometry (6), to construct a pseudo-double-beam atomic absorption spectrometer (7), to carry out qualitative and quantitative flame emission spectrometry (8), and to correct and compensate for monochromator misalignment (9). In the present application, the modulation technique is employed to greatly reduce the effect of flame background or broad-band spectral interference on a detected flame emission signal.…”

Computer-controlled programmable monochromator system with automated wavelength calibration and background correction

“…This integration time is important in both the spectral alignment procedure and the background correction cycle, particularly for weak emission lines. Hieftje and Sydor (36) concluded that signal averaging for 256 scans was essential for their sinusoidal demodulation step.…”

“…Quartz refractor plates have been incorporated in several previously described systems, typically to obtain derivative spectra during a wavelength scan with the use of lock-in amplifiers (25,26,(32)(33)(34)(35). Hieftje and Sydor (36) have examined the application of wavelength modulation to minimize spectrometer misalignment. A vibrating quartz plate was used to modulate the output wavelength and several demodulation approaches were analyzed and evaluated.…”

Physical characterization of the helium-oxygen-acetylene flame as an atom cell for atomic spectrometry

“…18AT10/2, General Electric Co., Cleveland, Ohio). Detection of the reversed condition (indicating equality of the lamp and flame temperatures), as described by Snelleman (11), was simplified by use of a wavelength-modulated monochromator and synchronous detection system (12).…”