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Related Concept Videos

IR Spectrometers01:25

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: Overview01:09

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 Spectroscopy: Molecular Vibration Overview01:24

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...
IR Frequency Region: Fingerprint Region01:03

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 C=O, C=N, and C=C occur between 1600–1850 cm−1.
The...
IR Frequency Region: X–H Stretching01:24

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 the 3500–3100 cm−1 range. Even though both O−H and N−H bonds vibrate at a similar...
IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations01:08

IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations

Identical bonds within a polyatomic group can stretch symmetrically (in-phase) or asymmetrically (out-of-phase). Similar to hydrogen bonding, these vibrations also influence the shape of the IR peak. Generally, asymmetric stretching frequencies are higher than symmetric stretching frequencies. For example, primary amines exhibit two distinct IR peaks between 3300–3500 cm−1 corresponding to the symmetric and asymmetric N-H stretching, while secondary amines exhibit a single stretching vibration...

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Related Experiment Video

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Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing
10:42

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

Published on: March 22, 2019

Widely tunable difference frequency generation source for high-precision mid-infrared spectroscopy.

Chun-Chieh Liao1, Yu-Hung Lien, Kuo-Yu Wu

  • 1Department of Physics, National Tsing Hua University, Hsinchu, Taiwan.

Optics Express
|April 24, 2013
PubMed
Summary

We created a tunable mid-infrared laser source for precise molecular spectroscopy. This new laser system achieves high accuracy in measuring carbon dioxide (CO2) transition frequencies.

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Last Updated: May 12, 2026

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Published on: March 22, 2019

Characterizing Far-infrared Laser Emissions and the Measurement of Their Frequencies
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Implementation of a Reference Interferometer for Nanodetection
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Area of Science:

  • Laser physics
  • Spectroscopy
  • Nonlinear optics

Background:

  • Developing tunable laser sources is crucial for high-resolution molecular spectroscopy.
  • Mid-infrared (MIR) lasers are essential for probing vibrational-rotational transitions in many molecules.

Purpose of the Study:

  • To develop a widely tunable mid-infrared difference frequency generation (DFG) laser source.
  • To demonstrate the application of this DFG source in high-resolution spectroscopy of carbon dioxide (CO2).

Main Methods:

  • Difference frequency generation (DFG) by mixing Ti:sapphire and Nd:YAG laser beams in MgO-doped periodically poled lithium niobate (MgO:PPLN).
  • Frequency stabilization of pump lasers and measurement using an optical frequency comb.
  • High-resolution saturation spectroscopy of CO2 transitions.

Main Results:

  • A widely tunable DFG source (2.66-4.77 μm) with > 2 mW power and ~100 kHz linewidth was developed.
  • Precise frequency control and determination (< 12 kHz) of the DFG source were achieved.
  • Absolute transition frequencies of CO2 were measured with accuracy better than 30 kHz.

Conclusions:

  • The developed DFG source is a versatile tool for high-resolution molecular spectroscopy.
  • The system enables accurate measurements of molecular transition frequencies in the mid-infrared region.
  • This work advances capabilities for spectroscopic studies of molecules like CO2.