Raman Spectroscopy

Detection of scattered light

Raman spectroscopy is based on the detection of scattered light. Due to interactions between electromagnetic radiation and molecular bonds, the detected light (Raman-scattering) has a different wavelength than the exciting laser. This is due to the fact that the molecules are set into oscillations. This means that energy of the incident light is absorbed or self-energy is given off to the light waves. This changes the frequency of the light and consequently the wavelength.

Rayleigh scattering, Stokes and anti-Stokes radiation

Rayleigh scattering (no change in excitation wavelength) is differentiated from Stokes and anti-Stokes radiation. Rayleigh scattering occurs when an elastic collision takes place between an incident photon and an electron. The electron is raised to a short-lived higher energy level by energy absorption and finally falls back to its base level by releasing the same energy. If the photon excites an oscillation, vibration or rotation, a part of the energy is transferred to the atom/molecule. It therefore remains at an energetically higher state, which means that only part of the radiated energy is released again. This is called Stokes-scattering. The wavelength of this scattering is usually given as the difference to the wavelength of the excitation radiation in wavenumbers (cm-1). When an already existing oscillation gives its energy to the incident photons, involved electrons fall back to the ground level. In this case, we speak of anti-Stokes scattering, whose wavenumber results from the involved energy levels in sum to the excitation wavelength. In the wavenumber spectrum, Stokes and anti-Stokes are arranged axisymmetrically with respect to the Rayleigh wavelength (corresponding to 0 cm-1) and are specific for the present form of chemical bonds. Thus, molecular bonds can be identified on the basis of a Raman spectrum.

Laser for UV Raman spectroscopy

266 nm cw lasers are a common light source for UV Raman spectroscopy. Since Raman scattering is always related to the excitation wavelength, there is a major advantage here: in many Raman investigations, fluorescence occurs that overlays the Raman signal. This mostly happens when Raman is excited with lasers in the visible spectral range, since fluorescence signals are usually visible as well. But when excited with a UV laser, the fluorescence remains in the visible and the Raman scattering moves into the UV region relative to the excitation radiation. Fluorescence and Raman signals can therefore be separated by UV lasers, making analysis much easier.

Related products:

2024-03-14T14:29:52+00:00

FQCW266-10

  • Power: 10 mW
  • Linewidth: < 300 kHz
  • Coherence length: > 1000 m
  • Beam quaility M2: < 1.3
  • Fundamental mode: TEM00
2024-03-14T14:33:10+00:00

FQCW266-25

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FQCW266-50

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FQCW266-100

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  • Linewidth: < 300 kHz
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FQCW266-200

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FQSS213-Q1

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2023-01-19T14:20:12+00:00

FDSS532-Q2

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