06-09-2017, 02:48 PM
Raman spectroscopy (named by Sir C. V. Raman) is a spectroscopic technique used to observe vibrational, rotational and other low-frequency modes in a system. Raman spectroscopy is commonly used in chemistry to provide a structural fingerprint through which molecules can be identified.
It is based on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near the infrared or near the ultraviolet range. Laser light interacts with molecular vibrations, photons, or other excitations in the system, resulting in the energy of laser photons moving up or down. The change in energy gives information about the vibrational modes in the system. Infrared spectroscopy provides similar but complementary information.
Typically, a sample is illuminated with a laser beam. The electromagnetic radiation of the illuminated spot is collected with a lens and sent through a monochromator. The elastic scattered radiation at the wavelength corresponding to the laser line (Rayleigh scattering) is filtered by a notch filter, an edge-pass filter or a band-pass filter, while the remainder of the collected light is dispersed on a detector.
Spontaneous Raman scattering is typically very weak, and as a result the main difficulty of Raman spectroscopy is to separate the weak inelastically scattered light from the intense scattered Rayleigh light. Historically, Raman spectrometers used holographic grids and multiple dispersion stages to achieve a high degree of laser rejection. In the past, photomultipliers were the detectors of choice for dispersive Raman configurations, resulting in long acquisition times. However, modern instrumentation almost universally employs notch or edge filters for laser rejection and spectrographs such as axial transmitters (AT), Czerny-Turner (CT) or FT (Fourier transform-based spectroscopy) monochromators and detectors CCD.
Advanced types of Raman spectroscopy include enhanced surface Raman, Raman resonance, Raman Raman Raman, Raman polarized, Raman stimulated (analogous to stimulated emission), Raman Raman, spatially compensated Raman, and hyper Raman.
It is based on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near the infrared or near the ultraviolet range. Laser light interacts with molecular vibrations, photons, or other excitations in the system, resulting in the energy of laser photons moving up or down. The change in energy gives information about the vibrational modes in the system. Infrared spectroscopy provides similar but complementary information.
Typically, a sample is illuminated with a laser beam. The electromagnetic radiation of the illuminated spot is collected with a lens and sent through a monochromator. The elastic scattered radiation at the wavelength corresponding to the laser line (Rayleigh scattering) is filtered by a notch filter, an edge-pass filter or a band-pass filter, while the remainder of the collected light is dispersed on a detector.
Spontaneous Raman scattering is typically very weak, and as a result the main difficulty of Raman spectroscopy is to separate the weak inelastically scattered light from the intense scattered Rayleigh light. Historically, Raman spectrometers used holographic grids and multiple dispersion stages to achieve a high degree of laser rejection. In the past, photomultipliers were the detectors of choice for dispersive Raman configurations, resulting in long acquisition times. However, modern instrumentation almost universally employs notch or edge filters for laser rejection and spectrographs such as axial transmitters (AT), Czerny-Turner (CT) or FT (Fourier transform-based spectroscopy) monochromators and detectors CCD.
Advanced types of Raman spectroscopy include enhanced surface Raman, Raman resonance, Raman Raman Raman, Raman polarized, Raman stimulated (analogous to stimulated emission), Raman Raman, spatially compensated Raman, and hyper Raman.