Journal Article

Coherent Raman spectro-imaging with laser frequency combs

Holzner, Simon, Picqué, Nathalie, Hänsch, Theodor W., Guelachvili, Guy, Bernhardt, Birgitta, Ideguchi, Takuro

2013

Overview

A new multiplex technique of coherent anti-Stokes Raman spectro-imaging with two laser frequency combs is shown to record molecular spectra of broad bandwidth on a microsecond scale. Raman spectroscopy with laser frequency combs Advances in optical spectroscopy and microscopy have had a profound impact throughout the physical, chemical and biological sciences. Particularly valuable are label-free methods capable of probing complex systems in a non-destructive and chemically sensitive manner, ideally with high spatial and temporal resolution. This is offered by coherent Raman spectroscopy, and here Takuro Ideguchi et al now show that it can be implemented using two laser frequency combs and thereby allow spectra covering a wide bandwidth to be measured with high resolution on a single detector on the microsecond timescale. With further system development, the method is expected to offer exciting new possibilities not only in spectroscopy but also for real-time microscopy observations of, for example, biological processes. Advances in optical spectroscopy and microscopy have had a profound impact throughout the physical, chemical and biological sciences. One example is coherent Raman spectroscopy, a versatile technique interrogating vibrational transitions in molecules. It offers high spatial resolution and three-dimensional sectioning capabilities that make it a label-free tool 1 , 2 for the non-destructive and chemically selective probing of complex systems. Indeed, single-colour Raman bands have been imaged in biological tissue at video rates 3 , 4 by using ultra-short-pulse lasers. However, identifying multiple, and possibly unknown, molecules requires broad spectral bandwidth and high resolution. Moderate spectral spans combined with high-speed acquisition are now within reach using multichannel detection 5 or frequency-swept laser beams 6 , 7 , 8 , 9 . Laser frequency combs 10 are finding increasing use for broadband molecular linear absorption spectroscopy 11 , 12 , 13 , 14 , 15 . Here we show, by exploring their potential for nonlinear spectroscopy 16 , that they can be harnessed for coherent anti-Stokes Raman spectroscopy and spectro-imaging. The method uses two combs and can simultaneously measure, on the microsecond timescale, all spectral elements over a wide bandwidth and with high resolution on a single photodetector. Although the overall measurement time in our proof-of-principle experiments is limited by the waiting times between successive spectral acquisitions, this limitation can be overcome with further system development. We therefore expect that our approach of using laser frequency combs will not only enable new applications for nonlinear microscopy but also benefit other nonlinear spectroscopic techniques.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/624/1107/527/1821 / 639/638/440/527/1821 / Absorption spectroscopy / Applied sciences / Electronics / Exact sciences and technology / Experiments / Fundamental areas of phenomenology (including applications) / Humanities and Social Sciences / Imaging and optical processing / Lasers / letter / Methods / Microscopy / multidisciplinary / Noise / Nonlinear optics / Optics / Optoelectronic devices / Physics / Raman spectroscopy / Science / Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices / Signal processing / Spectrum allocation / Spectrum analysis / Spectrum Analysis, Raman - instrumentation / Spectrum Analysis, Raman - methods / Time Factors / Ultrafast processes; optical pulse generation and pulse compression / Vibration