Purpose
Like its liquid counterpart, the didymium glass filter produces characteristic peaks that make it suitable for use as a wavelength reference material in the visible region of the spectrum.
Description and Discussion
Glass filters mounted ‘stress free’ in an anodised aluminium Glass filter containing didymium (a mixture of neodymium
& praseodymium) oxide, mounted stress free in an anodised aluminium holder. As a solid material the didymium glass filteris physically more robust than the equivalent liquid cell, and can therefore be used in more demanding environments, making it especially useful as a routine wavelength check. Sliding window covers are provided to protect the surface from damage when not in use. Variations from melt to melt of the glass can cause small uncertainties in peak position, soeach Starna filter is individually certified.
The spectrum shows 11 characteristic and well-defined peakscovering the wavelength range from 430 nm to 890 nm.
Approximate peak wavelength values (in nm) are: 431, 473, 513, 529, 573, 585, 685, 741, 749, 807, 879.
Note: The above values are for guidance only. Because theabsorption bands are asymmetric, measured values will bespectral bandwidth dependent. The Calibration Certificateaccompanying each Starna Didymium Glass Reference gives actual values measured at bandwidths of 0.10, 0.25, 0.50,1.00, 1.50, 2.00 and 3.00 nm, and only these certified values should be used for instrument qualification. On request, Starna can provide certified values at other wavelengths andbandwidth values.
