Featured | Tools | Test Equipment | Spectroradiometer | Jul 12, 2018

Stray Light Correction for Array Spectroradiometers

The core competency of Instrument Systems is providing high performance array spectroradiometers, e.g. the CAS 140D that features highest measurement accuracy and reliability. Quality and accuracy of a spectrometer are extremely important because all radiometric, photometric and colorimetric quantities are calculated from the spectral data. A considerable source of error is the occurrence of stray light in the device. This means that a certain pixel of the array detector is contaminated by radiation other than the targeted spectral component.

Instrument Systems developed the new CAS 140D array spectroradiometer with an improved mechanical and optical design that suppresses straylight to a very large extend. The excellent resulting stray light properties are even enhanced by using a stray light correction method. This ensures that  light sources even in the ultraviolet spectral range can be measured accurately (see Figure).

The complex stray light behavior of an array spectroradiometer can be determined with the aid of a tunable laser source. The idea is that monochromatic radiation can be attributed for the most part to a certain pixel of the detector. The entire light that is measured outside the bandpass function for this wavelength is the stray light contribution of pixel i that is seen from all other pixels j in the detector.

In practical implementation, wavelengths are tuned in steps within the measurement range of the spectroradiometer and the corresponding spectra are recorded. The tuning of the wavelength can be performed with the aid of an optical parametric oscillator (OPO) laser. The entirety of all detected spectra over all excitation wavelengths and suitable interpolation is recorded  in a device specific matrix. Finally the substraction of the bandpass function of the real signal results in a so-called stray light matrix. This stray light matrix can be numerically applied in the calibration and measurements of the spectrometer.

The unique advantage of array spectroradiometers is based on a fixed diffraction grating and a detector array, for example a CCD sensor. Since the entire spectrum is captured simultaneously by the detector array, very short measuring times can be achieved in the order of milliseconds. Moreover,array spectroradiometers are very robust and are ideal for industrial applications. Instrument Systems is the first industrial supplier who implements a stray light correction matrix in the calibration process of array spectroradiometers.

For additional information, please visit www.instrumentsystems.com/CAS140D or email sales@instrumentsystems.com

About Instrument Systems GmbH:

Instrument Systems GmbH develops, manufactures and markets turnkey solutions for light measurement. Its main products are array spectrometers, imaging photometers and colorimeters. Key applications are LED/SSL and display measurement, as well as spectroradiometry and photometry. Products of the Optronik line for the automotive industry and traffic technology are developed and marketed at the Berlin facility. Since 2012 Instrument Systems has been a wholly owned subsidiary of the Konica Minolta Group.