Wavelength Standards

Table II. Luminescence Wavelength Standards--Organics In Solution and Inorganic Ions In Glass Matrices...

The frequency stability obtained up to now is already better than 1x10 and therefore exceeds the accuracy of the optical wavelength standard (red krypton line) by more than three orders of magnitude 333b, c)... 

PDS), which is based on the use of moving windows that allow corrections to be applied in specihc spectral regions. Other methods used for this purpose include simple wavelength standardization (SWS), multivariate wavelength standardization (MWS) and direct standardization (DS). 

RTA real-time assurance SWS simple wavelength standardization... 

Holmium oxide solution is commercially available in a sealed 1-cm cuvette. It is a very convenient and versatile wavelength standard. The standard is suitable for UV-Vis spectrophotometers typically used in pharmaceutical laboratories, with spectral bandwidth ranging from 2 to 0.5 nm. The certified wavelength values of the peaks are listed in Table 10.3. When a spectral bandwidth of... 

In case there is a need to perform wavelength accuracy and photometric accuracy measurements for the far-UV region below 240 nm, there are new certified reference standards available from Stama Cell [18]. The wavelength standard is a solution of rare earth oxides solvated in dilute sulfuric acid. The standard exhibits well-characterized absorption bands at 210, 211, 222, 240, and 253 nm (Figure 10.13). The photometric accuracy standard consists of a series... 

Holmium Oxide Solution Wavelength Standard from 240-640 nm, SRM 2034, NIST Spec. Publ. 260-102, 1986. 

J. C. Travis et al., Intrinsic Wavelength Standard Absorption Bands in Holmium Oxide Solution for UV/Visible Molecular Absorption Spectrophotometry, J. Phys. Chem. Ref. Data 2005,34, 41. 

Utilization of data obtained from various plasma sources (e.g. beam-foil, tokamak and laser-produced plasma [287]) enabled the identification with high accuracy of the lines of highly ionized atoms in solar spectra. A special commision No 14 on Atomic and Molecular Data of the International Astronomical Union coordinates the activity on systematization of spectroscopic data, informs the astrophysics community on new developments and provides assessments and recommendations. It also provides reports which highlight these new developments and list all important recent literature references on atomic spectra and wavelength standards, energy level analyses, line classifications, compilations of laboratory data, databases and bibliographies. 

Although it may seem more like a problem for a linguistic philosopher it is necessary briefly to make quite clear what is meant by a spectroscopic constant . Unfortunately spectroscopic constants are not immutable quantities measured by spectroscopists to an accuracy solely dependent on the quality of his measuring instruments and the precision of wavelength standards. The measured quantities which are in this position are the spectroscopic lines and hence the term values. These may be measured and quoted in terms of wave numbers with statistical limits on their accuracy.2... 

Determination of Raman shift with absolute wavelength standards always requires subtraction of two frequencies, those for the laser and the Raman... 

A wavelength standard should possess characteristics which permit its ready redetermination in other laboratories by different techniques. Considering all of the factors involved in the selection of a wavelength standard, the W Kai line is superior to any other x-ray or 7-ray wavelength. Its advantages as the x-ray wavelength standard are discussed in Review of Modem Physics Vol. 39, page 82 (1967). 

This is a new unit of length which may differ from the angstrom by 5 ppm (probable error), hut as a wavelength standard it has no error. In order to clearly indicate that this unit is not exactly an angstrom, it has been designated A. ... 

The wavelength uncertainty test verifies the accuracy and precision of the spectrophotometer x-axis. Typically, the x-axis will be in nanometers for a dispersion instrument and cm for a FT instrument. The use of cm for the spectral axis of an FT instrument is due to the mathematics of the interference term (Atkins 1996). The wavelength standards have stable isolated peaks usually based on a mixture of rare-earth oxides. The center of mass of the peaks is compared to standard values established on master instruments at National Institute of Standards and Technology (NIST). The typical tolerance values for the peak accuracy are 1 nm [19]. The observed precision values are usually much smaller than 1 nm due to the high reproducibility of modern spectrophotometers. The photometric linearity verifies that the y-axis of the spectrophotometer is linear over a typical refiectance range. The linearity is verified by scanning a series of standards of known reflectance (absorbance) values. The measured absorbance is plotted versus the standard values. The USP chapter specifies that the slope of this curve is equal to 1.0 0.05 with an intercept of 0.0 0.05. Photometric standards are available from instrument vendors and third party suppliers. 

As in the case of dispersive Raman spectrometers (cf Section 4.4.1), it is necessary to calibrate the wavelength scale of dispersive UV/VIS spectrometers. The most accurate standards for checking the UV/VIS wavelengths are lasers of various types. The inexpensive helium-neon laser can be used to check at 632.8 nm. For spectrometers with a deuterium source, spectral lines at 486.6 and 656.1 nm can be used for calibration. A common method for wavelength calibration is the use of optical filters. A filter of didymium glass has many sharp absorption peaks, which can be used as a second wavelength standard (precision within 0.5 nm). 

Allen DW (2007) Holmium oxide glass wavelength standards. J Res Nad Inst Stand Technol 112 303-306... 

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