A compact laser platform for nonlinear Raman microspectroscopy: multimodality through broad chirp tunability

Abstract

We demonstrate a compact laser platform that integrates stimulated and coherent Raman microscopy with high-resolution nonlinear Raman spectroscopy. Ultrashort laser pulses with a carefully managed, broadly tunable chirp are shown to enable a comfortable switching between the high-contrast microscopy and high-resolution spectroscopy modalities in both stimulated and coherent versions of nonlinear Raman scattering. Sub-10-cm À1 spectral resolution in stimulated Raman spectroscopy is demonstrated through a careful compensation of nonlinear phase distortions of ultrashort laser pulses. This offers a powerful tool for a reliable identification of molecular vibrations with close frequencies, enhancing the chemical selectivity of spectroscopic analysis of complex multicomponent systems. Introduction and Wolfgang Kiefer's legacyHigh-resolution spectroscopic analysis and ultrafast, short-pulse interrogation are the two main modalities of optical technologies based on nonlinear Raman scattering. [1,2] While high-resolution Raman spectroscopy [3,4] requires narrowband probes, capable of resolving individual molecular or atomic features in often crowded Raman spectra of complex chemical systems, broadband, shortpulse drivers offer a vast arsenal of tools [5,6] for time-resolved studies of ultrafast dynamics in physical, chemical, and biological systems [1,2,7] and open a whole new world of chemically specific, high-speed nonlinear microscopy. [8][9][10] The requirements on laser fields needed to implement these modalities are seemingly incompatible.Wolfgang Kiefer, one of the pioneers of the field of Raman spectroscopy, whose work had a profound impact on the field and who prominently contributed to the development of high-spectralresolution Raman methods, [11,12] was also among the first visionary scientists who recognized the tremendous potential of emerging short-pulse laser sources for Raman technologies. [13][14][15] This vision has in many ways shaped the future of the field. Within the past two decades, nonlinear Raman processes driven by ultrashort pulses have played a central role in ultrafast science, providing methods that help to probe [16,17] and control [18][19][20][21] ultrafast processes on the picosecond, femtosecond, and attosecond time scale, [22] as well as open new horizons in standoff detection [23,24] and ultrashort waveform synthesis. [25,26] With a powerful impetus gained from the invention of nonlinear Raman microscopy, [8,27] short-pulse Raman techniques find growing applications in bioimaging, enabling a chemically selective, high-frame-rate detection of intracellular dynamics, [28] diagnostics of lipid membranes, [29] and neurophysiological studies. [30][31][32][33][34] Ultrashort laser pulses inevitably impose limitations on the spectral resolution in nonlinear-optical microspectroscopy, making it difficult to resolve closely lying and overlapping lines in Raman spectra and to extract the informative signal in the microscopy of multicomponent biological systems. However, the coherence of laser p...

Recent advances in linear and non‐linear Raman spectroscopy. Part XI

“…The instrument integrates stimulated and coherent Raman microscopy with high‐resolution non‐linear Raman spectroscopy. Ultrashort laser pulses with a carefully managed, broadly tunable chirp are shown to enable a comfortable switching between the high‐contrast microscopy and high‐resolution spectroscopy modalities in both stimulated and coherent versions of non‐linear Raman scattering . Sahlberg and co‐workers demonstrated nonintrusive, in situ detection of ammonia in hot gas flows with mid‐infrared degenerate four‐wave mixing at 2.3 μm.…”

“…Ultrashort laser pulses with a carefully managed, broadly tunable chirp are shown to enable a comfortable switching between the high-contrast microscopy and high-resolution spectroscopy modalities in both stimulated and coherent versions of non-linear Raman scattering. [100] Sahlberg and co-workers demonstrated nonintrusive, in situ detection of ammonia in hot gas flows with mid-infrared degenerate four-wave mixing at 2.3 μm. These results show the potential of IR-DFWM for detection of NH 3 in combustion environments.…”

Femtosecond-Laser-Pulse Characterization and Optimization for CARS Microscopy

“…In fact, simplified implementations are often used: in Ref. [ 26 ] XFROG SFG traces are recorded using a Fourier-transform-limited pump-and-probe pulse to characterize the Stokes pulse and vice-versa. In the Supplementary Information ( S3 Fig ) we shall exploit this approach to test the assumption of Gaussian beam profiles.…”

Prof. Dr Dr h.c. Wolfgang Kiefer An appreciation of Wolfgang Kiefer on the occasion of his 75th birthday

“…These contributions submitted by scientists from several continents to JRS nicely feature a diverse range of Raman spectroscopic approaches and their broad applicability. Many of the manuscripts deal with SERS, others cover topics such as instrumental developments and the application of Raman spectroscopy on biomolecular systems and materials …”

“…These contributions submitted by scientists from several continents to JRS nicely feature a diverse range of Raman spectroscopic approaches and their broad applicability. Many of the manuscripts deal with SERS, [1][2][3][4][5][6] others cover topics such as instrumental developments [7,8] and the application of Raman spectroscopy on biomolecular systems [9][10][11][12] and materials. [13,14] Wolfgang Kiefer worked throughout his impressive scientific career on pushing the limits of Raman spectroscopy, including the development of novel instrumental techniques, together with their application in a diverse range of scientific areas.…”