Transmission Measurements Part I: NIR OR VIS-NIR TRANSMISSION SPECTROSCOPY

Transmission spectroscopy is a widespread analysis technique that consists in measuring the absorption produced by a given sample when a beam of infrared light goes through them. Transmission spectroscopy applies mostly to liquids and gases, yet pressed powders or thin-films might also be characterized using this methodology. Besides spectroscopic measurements, transmission measurements are also useful to evaluate the properties of optical components, such as windows and filters. Arcoptix offers many solutions to perform transmission spectroscopy that rely either on our FT-NIR or MIR-FTIR instruments. 

NIR OR VIS-NIR TRANSMISSION SPECTROSCOPY

Liquid transmission spectroscopy is a standard spectroscopic measurement method that finds applications in various industrial and applied research fields, such as chemistry, biology, agriculture, food analysis, etc. Liquids are usually probed in the NIR using a fibered setup that includes a cuvette holder, which can host liquid cuvettes of different lengths. This makes the optical setup fairly straightforward to set in place, as no optical alignment is required. Other kind of samples, such as thin films can also be characterized using the same setup or a closely similar one.

In the NIR or the VIS-NIR, a transmission spectroscopy setup can be conveniently assembled using a fibered system that relies on a few elements:

Figure 1. Example of NIR Transmission Spectroscopy Setup

1. A fiber coupled light source based on a QTH bulb or equivalent such as the ARCLIGHT-NIR. The ARCLIGHT-NIR delivers a stable output and features a built-in blade diaphragm that allows to control the output light power.

2. A cuvette/sample holder with suitable focusing and collecting optics such as the Arcoptix CUV. The Arcoptix CUV can host cuvettes with optical paths going up to 1cm. It also features a slot dedicated to additional filters (intensity or color) or other samples (thin-films) that can be conveniently mounted with or in place of the cuvette.

3. High quality, low-loss optical fibers. Arcoptix offers standard low-OH fused silica fibers with a diameter core of 600um and standard lengths of 0.5m and 1m. Other fibers and fiber configurations (such as bundles) can be available on request, please contact Arcoptix directly for more information.

4. A FT-NIR or VIS-NIR fibered coupled instrument. The Arcoptix FTNIR-L1-025-2TE is the perfect tool for obtaining high quality and reproducible spectra with high SNR and sharp resolution. Alternatively, the Arcoptix VIS-NIR-FIB offers a compact and convenient solution for measuring the entire VIS-NIR spectrum down to 350nm. The VIS-NIR-FIB operates by stitching together the spectra acquired by our FT-NIR spectrometer and the one measured by a grating spectrometer for the visible region of the electromagnetic spectrum. Direct compatibility with other fibered systems and accessories is possible thanks to the usage of a Y-shaped fiber bundle that is used to connect simultaneously to the VIS and the NIR port of the instrument.