Equipment
Spectrometers
For measuring spectral reflectance, transmittance or transflectance of samples in the VIS (400 – 780 nm) and NIR (780 – 2500 nm) wavelength range.
ASD LabSpec® Pro (ASD Inc, Boulder, Co)
Wavelength range: 350 – 2500 nm
VIS module: Si diode array, range 350 to 1000 nm, 1.4 nm resolution
NIR module: post-dispersive scanning monochromator consisting of 2 peltier cooled InGaAs detectors, range 1000 to 2500 nm, 2 nm resolution) and controlled by the
Software: Indico Pro 6.0.3, RS3 6.0.9 and Labview
Zeiss Corona (Carl Zeiss AG, Jena, Germany):
Fibre VISNIR 1.7 for fiber optics (SMA905).
45 VISNIR 1.7 and 45 NIR1.7 for reflectance measurements: built-in OMK measurement head for diffuse reflectance measurements in a 45° configuration.
Single beam diode-array
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VIS module: Si array, range 306.5 to 1135.5 nm, 3.2 nm resolution
NIR module: InGaAs array, range 944.5 – 1710.9 nm, 6 nm resolution
Software: Aspect Plus 1.80 and Labview
Cameras
Baumer camera TXG14NIR
Digital Monochrome Matrix Camera, 1.4 Megapixels, Gigabit Ethernet connection.
Sensor type: SONY ICX285, 2/3“ interline progressive scan CCD with wavelength range 400-1000 nm, resolution 1392 x 1040 (pixel), exposure time 4 µsec-60 sec, 20 frames per second.
Xenics camera: Xeca-2.5-320
Flexible SWIR imaging camera, standard USB 2.0 or CameraLink connection.
The Xeva-2.5-320 unit is a compact digital camera, operating a HgCdTe detector array with 850-2500 nm sensitivity and 320 x 256 pixel resolution. Camera achieves excellent performance levels using a TE4-cooled device operating down to -73 °C or below.
Other Equipment
Double integrating spheres (DIS)
DIS allows to simultaneously measure the diffuse reflectance, diffuse transmittance and collimated transmittance of a particular sample (slab or in cuvette).
2 x Labsphere RT-060-IG integrating spheres:
The RT-060-IG spheres have a 6 inch inner diameter and are coated with Infragold®, designed for use in the 0.7 - 20 µm wavelength range. They feature five 1 inch diameter ports to accommodate sample and reference beams necessary for a 9° double or single beam geometry. A 0.5 inch detector port is located at the top of the sphere, baffled from receiving direct radiation from the sample and reference ports.
Optical table
The Tuned-Damped Field Upgradable optical table (M-ST-UT2-58-12, Newport Ltd.) has a 305 mm thickness, a 1500 mm width, 2400 mm length, and Metric M6 holes on a 25 mm grid.
Monochromator
The monochromator (Oriel Cornerstone 260, Newport Ltd.) with two mounted gratings offers a fast, automated and continuous scanning over a broad spectral range (450-2,800 nm). This monochromator is easy to be integrated into measurement application systems because of its other other standard features include a built-in electronic shutter, filter wheel control, USB 2.0 communications, and a family of interchangeable gratings and slits.
Supercontinuum laser
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The supercontinuum laser (SC450-4, Fianium Ltd.) offers a 4 W output power in total, and maintain a very high brightness across their entire wavelength spectrum (400 -2,400 nm) by generating ultrabroadband supercontinuum radiation. The output beam is well collimated and the power can be PC-controlled or manually adjusted.
Detectors
There are two 3mm diameter (G5853-23, Hamamatsu Ltd.) and two 1 mm diameter (PDA10DT-EC, Thorlabs ltd.) InGaAs detectors with extended wavelength range (1,200-2,570 nm). The Hamamatsu detectors are two-stage TE-cooled as provide ultrahigh sensitivity to measure weak light signals.
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Thorlab detector |
Hamamatsu detector |
Setups
Reflectance probe Spatially resolved spectroscopy (SRS)
As light from a source penetrates into a scattering sample, the photons are diffusely reflected and exit the sample in decreasing numbers as distance from the source increases. By capturing multiple spectrums at different distances from the source, the decay of the diffuse reflectance with increasing source-detector distance can be used to estimate the optical properties. This reflectance SRS-profile can be measured with a contact probe where different fibers are accurately placed at various distances from the illuminating fiber, by one collecting fiber if the distance between the illuminating and collecting fiber is controlled by a translation stage or contactless by means of hyperspectral imaging.
This setup, which was built in the lab, consists of a contact sensing probe with accurately placed fibres linked to a spectrograph for simultaneous measurement of the diffuse reflectance at the different distances by a CCD camera (400 – 1100 nm). One fibre serves as illumination fibre and others collect the diffuse reflected lights at different source-detector distances. The collected light from each of these fibres is guided to the entrance slit of a spectrograph which splits it into its spectral components and projects these onto a CCD camera. Controlling the setup and data acquisition are implemented by a LabView program developed in the lab.
Translation stage reflectance SRS
In this setup, the light is guided to the sample by a fiber, making contact. This creates a ‘glowing spot’ (see figure) in and on the sample. The reflected light is captured by another fiber, placed parallel to the first fiber, and is measured with a spectrometer. The spatial reflectance profile is obtained by collecting multiple spectra at different distances between the (fixed) source fiber and (movable) detection fiber. A translations stage is used to move the detection fiber at precise intervals.
The main components of the setup are a Zeiss Corona VISNIR 1.7 Fiber spectrophotometer with a spectral range of 400nm to 1700nm (Carl Zeiss, Jena, Germany), an Avalight 10W tungsten halogen light source (Avantes, Eerbeek, Netherlands), a ThorLabs 13mm XYZ-translation stage (New Jersey, USA) with fiber holder, two parallel 600-micron fibers in aluminum ferrule (Romack, Williamsburg, USA) and a fiber optical switch (Leoni, Neuhaus-Schierschnitz, Germany) to switch between sample and reference measurements.
Pre-dispersive hyperspectral scatter imaging setup
In this pre-dispersive hyperspectral scatter imaging setup, a monochromator splits up broad band light (400 – 2400 nm) from a super continuum laser source into many single-wavelength lights and sequentially illuminate a sample with each of these splitted lights. A camera is used to capture back-scattering lights at many wavelengths on the sample to acquire its hyperspectral scatter images. Controlling the laser light source, monochromator and data acquisition from the camera are implemented by a LabView program (National instruments, TX, USA). This setup provides a non-contact way for scattering analysis of the sample, which could be a potential for on-line applications.
Post-dispersive hyperspectral scatter imaging setup
A hyperspectral scatter imaging system for contactless determination of spatially resolved profiles from selected food samples has been developed. The system consists of a CCD camera (TXG14, Baumer, Germany) with optical sensitivity from 400-1000 nm and 1392 by 1040 pixel image resolution, a prism-grating-prism-based imaging spectrograph (ImSpector V10, Spectral Imaging Ltd., Oulu, Finland) covering the working spectral range between 325 and 990 nm, a focusing lens with 5 mm extender, and a light source with quartz tungsten halogen lamp (Alphabright, East Sussex, UK ) coupled into a fiber with collimating lens (Ocean Optics, Duiven, Netherlands), and a controlled moving stage with adjustable sample holder. The system is operated using LabView V8.5 (National Instruments, Austin, TX, USA).
Hyperspectral diffuse reflectance imaging setup
The hyperspectral diffuse reflectance imaging setup consists of four main components: a sample transportation plate, two 150W halogen lamps, an ImSpector V10 spectrograph (Spectral Imaging Ltd., Oulu, Finland) coupled with a standard C-mount zoom lens (Cosmicar, Japan), and a monochrome CCD camera KP-F120 (Hitachi Denshi Ltd., UK). The sample transportation plate and the two halogen lamps are installed inside a dome painted with a special white paint which provides very good diffuse reflection of the light. The two lamps emit light towards the dome and the light reflected by the dome subsequently illuminates the sample. When the transportation system operates, the sample is gradually moved through the field of the line-scanning spectrograph, such that each line is imaged. The zoom lens focuses each line on the sample onto the entrance slit of the spectrograph (80 µm width). Subsequently, an optical assembly (prism-grating-prism) inside the spectrograph disperses this first line-scan image into many secondary line-scan images depending on its wavelengths and projects them onto the CCD sensors of the camera. The camera sensors record each measured line-scan area on the sample as a 2D spatial-spectral matrix. A computer system and LabView software (National Instruments Corporation, Austin, USA) are used to capture all the line-scan images which enable to create hyperspectral diffuse reflectance data.
Transmittance measurement setup with laser, monochromator and detectors
The lab has state of the art, dual beam, pre-dispersive, fibre optics based systems from transmittance measurements. The system has the flexibility to be used as open space as well as fibre connected transmittance measurement system.
The light source used in the current setup is supercontinuum laser (SC450-4, Fianium Ltd.), which has nearly 4 W output power and very high brightness covering from visible to NIR range spectrum (400-2400 nm). Use of laser light source enables to achieve high signal to noise ratio (SNR) over the full spectrum range (400-2400 nm) even if the samples are scattering in nature, in which case, a significant amount of light might get scattered yielding low SNR especially in NIR region. The measurements are done in pre-dispersive mode, where the light is split using a monochromator (Oriel Cornerstone 260, Newport Ltd.) having two mounted gratings, which offers fast, automated and continuous scanning over a broad spectral range (450-2,800 nm). The light coming out from the monochromator has a wavelength accuracy of 0.35 nm with maximum resolution of 0.10 nm. The output light from monochromator falls onto the beam splitter, which splits the light into two near equal proportioned light beams, one of which is made to fall directly onto the reference detector and the other beam onto the cuvette containing the sample to be measured. The transmitted light from the sample is directed to the sample detector. Dual beam configuration is installed in the system to compensate for external factors such as laser light fluctuations, and it employs two 1 mm diameter (PDA10DT-EC, Thorlabs ltd.) InGaAs detectors with extended wavelength range (1,200-2,570 nm) for reading the voltage output from reference and sample arm. The net spectrum of the sample is obtained by dividing the output from sample arm by the output of reference arm, both of which are time-synchronised.
