FTIR (Fourier Transform Infrared Spectroscopy)

FTIR is a popular technique in many spectroscopy spaces. First, a sample (solid, liquid, or gas) is irradiated with infrared light, and then transmitted light or reflected light is interfered using an interferometer, creating an interferogram. Performing a Fourier transform function on this data provides the spectral output. Analysis is then done on the qualitative, quantitative, and identifying features of substances based on that spectral information. This method is used in various fields, including chemical analysis, medical treatment, environmental analysis, and material analysis, in the form of an FTIR analyzer or an FTIR spectrophotometer.

Hamamatsu products for FTIR

Hamamatsu offers spectroscopic modules and infrared detectors suitable for FT-NIR and FTIR.

Hamamatsu spectroscopic modules and infrared detectors suitable for FT-NIR and FTIR

For FT-NIR

FTIR engine (FT-NIR spectrometer)

The FTIR engine is a Fourier transform spectroscopic module that integrates an optical interferometer and a control circuit in a compact housing. It has high sensitivity in the near-infrared region (wavelengths: 1.1 to 2.5 μm). It fits in the palm of your hand, and can be incorporated into an FTIR analyzer. This contributes to the miniaturization and portability of benchtop FTIR analyzers, which were the mainstream FTIR instruments until now.

Features of FTIR engine

Detection performance on par with benchtop FTIR equipment

To eliminate the decrease in incident light level caused by miniaturization, we used Hamamatsu's original MEMS technology to develop a movable mirror that composes the actuator inside the optical interferometer, then improved upon it so that the reflected light can be used efficiently. Furthermore, we integrated the movable mirror and the fixed mirror as a MEMS chip, thereby making it compact and reducing error in the relative angle between the mirrors to about 1/100. By optimizing the structure and drive method of the MEMS actuator and eliminating blurring when in operation, we have suppressed the spread of infrared light inside the optical interferometer and reduced loss. By doing so, we have realized detection performance comparable to conventional benchtop type devices.

High wavelength reproducibility

Optical interference occurs when the light being measured (incident light) is split by a beam splitter, reflected by the movable mirror and fixed mirror, then combined again. Interference light intensity, which changes depending on the position of the movable mirror, is detected by a photodetector (InGaAs PIN photodiode), and then the signal is subjected to arithmetic processing (Fourier transform) to obtain the optical spectrum. By measuring the position of the movable mirror inside the interferometer using a photodetector (Si PIN photodiode) and semiconductor laser (VCSEL), it is possible to obtain an optical spectrum with high wavelength reproducibility.

Optical system of FTIR engine

FTIR engine measurement examples

Reflection measurement (absorbance comparison of sugar)

Comparing the reflection measurement results of sugar powder samples (glucose, sucrose, and fructose) from the FTIR engine and from a benchtop spectrometer, we found it was possible to accurately measure even minute peak patterns with the FTIR engine, similar to spectra obtained with the benchtop spectrometer.

Transmission measurement (comparison of absorbance of alcoholic beverages and estimation of alcohol concentration)

In the near-infrared region from 1.1 to 2.5 μm, there is absorption by OH groups in water (1.45 μm band, 1.9 μm band) and absorption by CH groups of alcoholic beverages (2.1 to 2.5 μm). With transmission measurement results, we were able to obtain the characteristic spectrum in the absorption bands of water and alcoholic beverages. In addition, using alcohol concentrations estimated from the absorbance in the 2.3 µm band, we confirmed that the estimated values and actual values of components contained in the beverages matched, and that high accuracy measurement is possible.

FTIR engine applications

We expect to find many applications for FTIR engines in a wide range of situations where it was difficult to make measurements in a timely manner, including pre-harvest inspection of agricultural products, soil analysis, and plastic sorting.

For FTIR

Type Ⅱ superlattice infrared detector

This is an infrared detector for FTIR, given sensitivity up to the 14 μm band using Hamamatsu's original crystal growth technology and process technology. It does not contain mercury or cadmium, which are RoHS regulated substances, so it can be used as a substitute for MCT photovoltaic detectors.

Type Ⅱ superlattice infrared detector features

High sensitivity up to the 14.5 μm band

With this innovation, we achieved a cutoff wavelength of 14.5 μm without using hazardous materials like MCT. This technology also has excellent linearity that enables a wide dynamic range, factors that can contribute to higher accuracy and simpler integration for FTIR analyzers.

Amplified integrated module available.

We also offer the C15780-401 infrared detection module with preamplifier, which comes equipped with the type Ⅱ superlattice infrared detector. Similar to the MCT detector, no power supply to the detector is necessary, so it can run with low current consumption.