August 2016
Spotlight Summary by Shalin Mehta
Exploring the potential of tailored spectral focusing
The inelastic scattering of light, during which a molecule either absorbs energy from or adds energy to the incident photon, provides a unique probe to study the chemical nature of materials. The discovery by C. V. Raman that vibrational frequencies of molecules match the far infrared region of the electromagnetic spectrum has enabled measurement of the chemical nature of materials, living and non-living, by exploiting inelastic scattering of light by molecular vibrations. This light-matter interaction, called Raman scattering, is now exploited in the form of Coherent Anti-Stokes Raman Spectroscopy (CARS). When implemented in imaging mode, CARS reveals the spatial distribution of specific chemical bonds without requiring an external label. CARS relies on three wave mixing which can resonantly drive specific vibration modes, or Raman lines, of the molecules. CARS does not deposit any energy in the molecule by itself and enhances weak Raman scattering signal so that available optical detectors can be used for measurement.
Key challenges in using CARS microscopy are 1) rejecting non-resonant background scattering that can mask the Raman signal characteristic of molecular vibrations, and 2) tuning the wavelength of incident light beams to probe a range of molecular vibrations. In the present paper, L. Brückner, T. Buckup, and M. Motskus from Heidelberg University report a novel solution to overcome these challenges. They propose and demonstrate the use of laser light whose frequency is changed at a constant rate over time (that is, it is chirped) for CARS imaging. Shaping the pulses of all three wavelengths offers unique experimental advantages to drive resonances of specific Raman lines and tuning the imaging system to different Raman lines. The authors exploit this experimental advantage of chirped pulses to obtain multi-modal images of human skin. This article presents an interesting advance in the experimental implementation of CARS microscopy.
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Key challenges in using CARS microscopy are 1) rejecting non-resonant background scattering that can mask the Raman signal characteristic of molecular vibrations, and 2) tuning the wavelength of incident light beams to probe a range of molecular vibrations. In the present paper, L. Brückner, T. Buckup, and M. Motskus from Heidelberg University report a novel solution to overcome these challenges. They propose and demonstrate the use of laser light whose frequency is changed at a constant rate over time (that is, it is chirped) for CARS imaging. Shaping the pulses of all three wavelengths offers unique experimental advantages to drive resonances of specific Raman lines and tuning the imaging system to different Raman lines. The authors exploit this experimental advantage of chirped pulses to obtain multi-modal images of human skin. This article presents an interesting advance in the experimental implementation of CARS microscopy.
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Article Information
Exploring the potential of tailored spectral focusing
L. Brückner, T. Buckup, and M. Motzkus
J. Opt. Soc. Am. B 33(7) 1482-1491 (2016) View: Abstract | HTML | PDF