A NIST traceable light source to enable radiometric correction of a spectrometer output. Primarily for use with any microscope based spectrometer system

“SYLPH™” Standard Yield Lamp for Photonic Calibration

How The SYLPH Hyperspectral Radiometric Calibration Light Source Works

Why Calibrating A Hyperspectral Spectrometer Is Necessary: Instrument to instrument variability: Unless they have been “standardized” all spectrometers will characterize a reference emission spectrum differently. This is a function of many issues including variations in detector efficiency, bandpass and various system optics Uncertainties in wavelength ratios: If a sample spectrum covers an extended spectral range, wavelength ratios may vary between instruments due to instrumental component variables. If measuring accurate wavelength ratios is necessary then the data delivered by an instrument needs to be “normalized” to a standard. By using a NIST certified lamp spectra are acquired in power (µW/cm2/nm). However, in most optical assemblies, the power output will be relative not absolute. Without correction, data will be highly reproducible, yet wavelength ratios will be “precisely inaccurate.” The main wavelength dependent culprits include: • The quantum efficiency (QE) of the spectrum detector such as a CCD or CMOS camera or photomultiplier tube (PMT) • The wavelength versus efficiency profile of a diffraction grating or prism • Variations between electronic bandpass filters such as Acousto Optic Tunable Filters (AOTF), Liquid Crystal Tunable Filters (LCTF) or interferometers. • Optical coatings, lenses, mirrors, filters, polarizers and any other optic that is located between the sample and the detector Aliasing when the system fails to accurately reconstruct an analog spectrum into a digital format. The impact of all these influences are eliminated when a spectrum is acquired in %transmission, absorption, or %reflection. In these cases, the sample spectrum is divided by a spectrum of the illumination source that has also passed through the same system. However, in emission spectroscopy including LED, OLED photo-luminescance fluorescence, and Raman there is no illuminant spectrum to divide by. Therefore, in order to accurately reconstruct wavelength ratio intensities, it is necessary to apply a correction factor at each wavelength.

NIST Certified radiometric power spectrum as a function of wavelength in relative µW/cm2/nm

Relative spectrometer spectrum of the NIST lamp before correction in arbitrary units

After radiometric calibration a correction an instrument will acquire an identical spectrum to the NIST certification in µW/cm2/nm

The SYLPH, NIST Certified, Radiometric Calibration Solution The accepted way to normalize any spectrometer is to acquire a spectrum of NIST certified characteristics. For wavelength accuracy use an absolute light source such as the MIDL Hg/Ar emission lamp. For wavelength versus intensity use a NIST certified emission lamp such as the “SYLPH” radiometric calibration light source. The SYLPH radiometrically calibrated light source delivers a stable, NIST-certified spectrum of known characteristics. This provides a spectral microscope or spectral confocal system with a certified traceable “reference emission.” To standardize a system determine a correction curve by acquiring a spectrum of the SYLPH lamp and compare it to the spectrum described in the certificate. After applying the correction curve the spectrometer will reconstruct the spectrum of the SYLPH lamp and accurately reconstruct the spectrum of any other sample. Once this correction factor has been incorporated in the data processing software it should be applied to all future acquisitions. Bottom line: All radiometrically calibrated instruments will accurately reproduce the same reference spectrum. Once an instrument has been radiometrically corrected all spectra acquired on that instrument can be compared with those acquired on other radiometrically calibrated instrument.

SYLPH Radiometric Calibration System Specifications

LED spectrum before radiometric correction in arbrary units

LED spectrum after radiometric correction in relative µW/cm2/nm