Femtosecond broadband stimulated Raman spectroscopy: Apparatus and methods

McCamant, David W.; Kukura, Philipp; Yoon, Sangwoon; Mathies, Richard A.

doi:10.1063/1.1807566

Cited by 288 publications

(378 citation statements)

References 40 publications

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“…The 500-nm actinic pump pulse (35 fs, 100 nJ) was produced by a noncollinear phase-matched optical parametric amplifier (NOPA), whose output was compressed with an SF10 prism compressor. A grating-based spectral filter 25 generated the 809-nm 3.5-ps Raman pump pulse that was attenuated to 400 nJ/pulse. The Raman pump power was chosen to limit removal of the excited-state population because of excited-state absorption and stimulated emission at the Raman pump wavelength.…”

Section: Methodsmentioning

confidence: 99%

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Femtosecond Stimulated Raman Study of Excited-State Evolution in Bacteriorhodopsin

2005

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Femtosecond time-resolved stimulated Raman spectroscopy (FSRS) is used to examine the photoisomerization dynamics in the excited state of bacteriorhodopsin. Near-IR stimulated emission is observed in the FSRS probe window that decays with a 400-600-fs time constant. Additionally, dispersive vibrational lines appear at the locations of the ground-state vibrational frequencies and decay with a 260-fs time constant. The dispersive line shapes are caused by a nonlinear effect we term Raman initiated by nonlinear emission (RINE) that generates vibrational coherence on the ground-state surface. Theoretical expressions for the RINE line shapes are developed and used to fit the spectral and temporal evolution of the spectra. The rapid 260-fs decay of the RINE peak intensity, compared to the slower evolution of the stimulated emission, indicates that the excited-state population moves in ∼260 fs to a region on the potential energy surface where the RINE signal is attenuated. This loss of RINE signal is best explained by structural evolution of the excited-state population along multiple low-frequency modes that carry the molecule out of the harmonic photochemically inactive Franck-Condon region and into the photochemically active geometry.

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Section: Methodsmentioning

confidence: 99%

“…25 The △t = 0 time delay was initially set by the crosscorrelation, but was allowed to vary freely in the fitting of the stimulated emission kinetics.…”

Section: Methodsmentioning

confidence: 99%

Femtosecond Stimulated Raman Study of Excited-State Evolution in Bacteriorhodopsin

2005

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“…The output of the laser is split into two parts that are used to produce the picosecond Raman and femtosecond continuum probe fields. The Raman pulse is generated by spectrally filtering the broadband output of the laser fundamental with an appropriate narrowbandpass filter (22). The probe is produced by focusing <1% of the output into a thin sapphire window to generate a broadband continuum that is subsequently compressed temporally by a system of prisms.…”

Section: Easier Than You Thinkmentioning

confidence: 99%

“…The two pulses are overlapped spatially with a broadband beam splitter and temporally with an optical delay line; this process is simplified by the picosecond duration of the Raman pulse (22). They are then focused on the sample with beam diameters of 40-100 µm.…”

Section: Easier Than You Thinkmentioning

confidence: 99%

Femtosecond Stimulated Raman Spectroscopy

Kukura

Yoon²,

Mathies³

2006

Anal. Chem.

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R aman spectroscopy is a powerful analytical technique for revealing vibrational structure. It is widely used in biology, chemistry, and studies of molecular reaction dynamics (1-3). One of the technique's greatest advantages is that a single spectrum contains a wealth of vibrational structural information about the sample. The large number of well-resolved vibrational bands provides unique information analogous to a human fingerprint, and the technique is very sensitive to molecular structure. Changes in bond lengths of as little as 0.01 Å can produce clear differences in the vibrational spectrum. This specificity and sensitivity make Raman an excellent tool for trace analysis and for studies of chemically induced structural changes.Although a wide variety of Raman techniques have been developed over the years and applied to analytical problems, significant room for improvement still exists. FT Raman methods are often used in industrial applications to avoid background fluorescence-via intense laser radiation in the NIR-and to exploit the FT multiplex advantage. Clinical applications of FT Raman range from identification of cancerous tissues to microscopic imaging (4). However, it can suffer from weak resonance enhancement and intense Rayleigh scattering caused by the noise distribution of the FT (5). In surface-enhanced Raman spectroscopy, spectra of molecules adsorbed to roughened metallic surfaces or nanostructures can be taken with extreme sensitivity; however, the technique relies on the not-easily-controlled interaction of the metallic substrates with the analyte (6). Raman imaging has recently been advanced through the use of nonlinear Raman techniques, in particular coherent anti-stokes Raman scattering (CARS), which has been used, for example, to monitor biological processes in real time (7,8). Despite these advances, limitations exist that prevent these methods from exploiting the full potential of Raman scattering. We asked: Can an analytical resonance Raman technique be developed that can produce high-S/N spectra that are immune to background fluorescence, with short data-acquisition times?Time-resolved vibrational spectroscopies are also extensively used in structural studies of dynamics of chemical and biological reactions. The earliest (<50-fs) events in photochemical and photophysical processes are best studied by resonance Raman intensity analysis, an extremely powerful technique that can provide detailed excited-state structural information (9, 10). Spontaneous time-resolved resonance A new approach for obtaining vibrational Raman spectra and for studying chemical reaction dynamics. 9 4 A N A LY T I C A L C H E M I S T R Y / S E P T E M B E R 1 , 2 0 0 6Raman spectroscopy is limited to the picosecond time domain because of the transform limit; this prevents the technique from being applied to chemical reactions that occur on the order of 10 f s-1 ps. This limitation has recently been overcome by the availability of femtosecond pulses in the IR. As a consequence, pump-probe approaches for measu...

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“…Specifically, it is subject to a time-energy resolution restriction dictated by the time-bandwidth product of the light pulse, which is limited by ΔEΔt ≥ 15 cm -1 ps (ref. 22).In this Letter, we circumvent this limitation by taking advantage of the unrestricted time precision and energy resolution of femtosecond stimulated Raman spectroscopy (FSRS) 23 , which we use to …”

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Probing ultrafast photo-induced dynamics of the exchange energy in a Heisenberg antiferromagnet

et al. 2015

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Manipulating the macroscopic phases of solids using ultrashort light pulses has resulted in spectacular phenomena, including metal-insulator transitions 1-3 , superconductivity 4 and subpicosecond modification of magnetic order 5 . The development of this research area strongly depends on the understanding and optical control of fundamental interactions in condensed matter, in particular the exchange interaction. However, disentangling the timescales relevant for the contributions of the exchange interaction and spin dynamics to the exchange energy, E ex , is a challenge. Here, we introduce femtosecond stimulated Raman scattering to unravel the ultrafast photoinduced dynamics of magnetic excitations at the edge of the Brillouin zone. We find that femtosecond laser excitation of the antiferromagnet KNiF 3 triggers a spectral shift of the two-magnon line, the energy of which is proportional to E ex . By unravelling the photo-induced modification of the twomagnon line frequency from a dominating nonlinear optical effect, we find that E ex is increased by the electromagnetic stimulus.Magnetic order is a macroscopic manifestation of the quantum phenomenon of exchange coupling between spins. Under thermodynamic equilibrium conditions, the energy of the interaction is conventionally described in the Heisenberg-Dirac formwhere E ex is the exchange energy, J ab is the exchange interaction, and the last term is the correlation function between spins on neighbouring sites a and b.Despite the enormous number of experiments reporting on the optical control of spins 5 , there are very few studies of the ultrafast photo-induced dynamics of the exchange interaction 6,7 . One of the reasons for the popularity of spin dynamics studies is the possibility to use all-optical techniques, which can be applied easily to a broad class of materials. However, the studies that have succeeded in revealing the dynamics of the exchange energy E ex make use of the rather demanding and less flexible technique of time-and spinresolved photoelectron spectroscopy. Despite its complexity, photoelectron spectroscopy has proven to be very powerful when applied to metal surfaces 6,7 . In these materials, however, ultrafast laser excitation also triggers electronic dynamics, which defines the dynamics of J, and demagnetization 8,9 , which is related to the spin correlation function, both on the femtosecond timescale. So, disentangling the dynamics of the two contributions appearing in equation (1) is challenging. In some semiconductors, the overall dynamics of the d-f exchange energy has been monitored by measuring the transient optical properties 10 . On the other hand, the scenario in dielectrics is markedly different. Although the timescale of the charges' response is still basically limited by the duration of a femtosecond stimulus, demagnetization occurs over a timescale as long as 100 ps after photoexcitation 11 . Assessing the capability of light to probe the exchange energy at the femtosecond timescale in such cases would therefore allow the dy...

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Femtosecond broadband stimulated Raman spectroscopy: Apparatus and methods

Cited by 288 publications

References 40 publications

Femtosecond Stimulated Raman Study of Excited-State Evolution in Bacteriorhodopsin

Femtosecond Stimulated Raman Study of Excited-State Evolution in Bacteriorhodopsin

Femtosecond Stimulated Raman Spectroscopy

Probing ultrafast photo-induced dynamics of the exchange energy in a Heisenberg antiferromagnet

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