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IR Spectrometers

IR Spectrometers

There are two main infrared (IR) spectrophotometers: dispersive IR spectrometers and Fourier transform infrared (FTIR) spectrometers. In a dispersive IR spectrometer, a beam of infrared radiation produced by a hot wire is divided into two parallel equal-intensity beams using mirrors. One beam passes through the sample, while another is a reference beam. The beams then move through the monochromator, which separates the radiations into a continuous spectrum of different frequencies. The...

Infrared (IR) Spectroscopy: Overview

Infrared (IR) Spectroscopy: Overview

When electromagnetic radiation passes through a material, atoms or molecules transition from a lower to a higher energy state by absorbing radiation corresponding to the energy difference between the two states. The absorption of infrared (IR) radiation causes transitions between vibrational energy levels in a molecule. Therefore, IR spectroscopy is a useful analytical tool for determining the molecular structure of molecules.
Different compounds display unique properties due to their...

IR Frequency Region: Fingerprint Region

IR Frequency Region: Fingerprint Region

IR spectra are divided into two main regions: the diagnostic region and the fingerprint region. The diagnostic region of the spectrum lies above 1500 cm−1. The absorptions resulting from single-bond vibrations of the N–H, C–H, and O–H stretch at higher wavenumbers and appear on the left side of the spectrum. The stretching absorptions of the C≡C and C≡N occur between 2100–2300 cm−1. In contrast, those arising from stretching absorptions of the...

IR Frequency Region: X–H Stretching

IR Frequency Region: X–H Stretching

In IR spectroscopy, signals produced by the X−H bonds (such as C−H, O−H, or N−H) can be observed in the frequency range of 2700–4000 cm–1. The C−H stretching vibration forms sharp bands in the region 2850–3000 cm–1. The presence of the O−H stretching vibration leads to the forming of an absorption band in the frequency range 3650–3200 cm−1. At the same time, N−H stretching can be confirmed by absorption bands in...

IR Spectrum

IR Spectrum

When infrared (IR) radiation passes through a molecule, the bonds stretch or bend by absorbing the radiation. This absorption creates the molecule's absorption spectrum, which is the plot of its percentage transmittance versus wavenumber.
Transmittance is defined as the ratio of the radiant power passing through a sample to that from the radiation's source. Multiplying the transmittance by 100 gives the percent transmittance (%T), which varies between 100% (no absorption) and 0%...

IR Spectroscopy: Molecular Vibration Overview

IR Spectroscopy: Molecular Vibration Overview

When Infrared (IR) radiation passes through a covalently bonded molecule, the bonds transition from lower to higher vibrational levels. The fundamental vibrational motions that result in infrared absorption can be classified as stretching or bending vibrations.
Stretching vibrations are vibrational motions that occur along the bond line, changing the bond length or distance between two bonded atoms. They are further distinguished as symmetric or asymmetric. In symmetric stretching, the...

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Related Experiment Video

Updated: May 16, 2025

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing

Published on: March 22, 2019

1060 nm interferometric near-infrared spectroscopy.

Dibbyan Mazumder, Santosh Aparanji, Oybek Kholiqov

|April 1, 2025

Summary

Investigating longer wavelengths for interferometric near-infrared spectroscopy (iNIRS) significantly boosts signal-to-noise ratio (SNR). This advancement enhances time-of-flight (TOF) resolved measurements in biological tissues.

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Area of Science:

Biomedical Optics
Spectroscopy
Photonics

Background:

Interferometric near-infrared spectroscopy (iNIRS) measures diffuse light fields with time-of-flight (TOF) resolution.
Current iNIRS methods face challenges with low signal-to-noise ratio (SNR).
Longer wavelengths offer potential for improved SNR due to tissue properties and safety.

Purpose of the Study:

To evaluate the performance of iNIRS at 1060 nm.
To assess the impact of longer wavelengths on SNR in TOF-resolved measurements.
To compare SNR at 1060 nm against shorter wavelengths (855 nm and 773 nm).

Main Methods:

Utilized interferometric near-infrared spectroscopy (iNIRS) at 1060 nm.
Measured diffuse light field fluctuations with time-of-flight (TOF) resolution.
Analyzed autocorrelation SNR across forehead locations at specific TOF ranges (800-1000 ps).

Main Results:

Achieved significant SNR improvements at 1060 nm compared to 855 nm (3.7-9.3 times) and 773 nm (6.0-33.5 times).
Observed improvements at TOFs of 800-1000 ps.
Attributed improvements to both physical system parameters and potential tissue responses.

Conclusions:

Wavelengths around 1060 nm show promise for enhancing iNIRS measurements.
Longer wavelengths can potentially overcome SNR limitations in TOF-resolved speckle fluctuation analysis.
This wavelength offers a pathway to more robust iNIRS applications.