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Time-domain spectroscopy in the mid-infrared.

Lanin AA, Voronin AA, Fedotov AB, Zheltikov AM - Sci Rep (2014)

Bottom Line: Here, we show that, with a combination of advanced ultrafast technologies and nonlinear-optical waveform characterization, time-domain techniques can be advantageously extended to the metrology of fundamental molecular motions in the mid-infrared.In our scheme, the spectral modulation of ultrashort mid-infrared pulses, induced by rovibrational motions of molecules, gives rise to interfering coherent dark waveforms in the time domain.These high-visibility interference patterns can be read out by cross-correlation frequency-resolved gating of the field in the visible generated through ultrabroadband four-wave mixing in a gas phase.

View Article: PubMed Central - PubMed

Affiliation: 1] Physics Department, International Laser Center, M.V. Lomonosov Moscow State University, Moscow 119992, Russia [2] Russian Quantum Center, ul. Novaya 100, Skolkovo, Moscow Region, 1430125 Russia.

ABSTRACT
When coupled to characteristic, fingerprint vibrational and rotational motions of molecules, an electromagnetic field with an appropriate frequency and waveform offers a highly sensitive, highly informative probe, enabling chemically specific studies on a broad class of systems in physics, chemistry, biology, geosciences, and medicine. The frequencies of these signature molecular modes, however, lie in a region where accurate spectroscopic measurements are extremely difficult because of the lack of efficient detectors and spectrometers. Here, we show that, with a combination of advanced ultrafast technologies and nonlinear-optical waveform characterization, time-domain techniques can be advantageously extended to the metrology of fundamental molecular motions in the mid-infrared. In our scheme, the spectral modulation of ultrashort mid-infrared pulses, induced by rovibrational motions of molecules, gives rise to interfering coherent dark waveforms in the time domain. These high-visibility interference patterns can be read out by cross-correlation frequency-resolved gating of the field in the visible generated through ultrabroadband four-wave mixing in a gas phase.

No MeSH data available.


Related in: MedlinePlus

(a) Time-domain spectral interferometry in the mid-infrared. When its central wavelength is tuned on resonance with a typical molecular rovibrational band, the mid-IR driver, due to its extremely large bandwidth, interacts with the entire manifold of rovibrational transitions, exciting a broadband rovibrational wave packet. As a part of this process, the energy is transferred from the mid-IR driver to molecular motion, giving rise to narrowband absorption features in the spectrum of mid-IR radiation at the frequencies of individual molecular modes, separated by spectral intervals ΔνP and ΔνR for the P and R rovibrational branches, respectively. In the time domain, these narrowband spectral dips translate into stretched dark field waveforms, as shown in the right panel. Due to the coherence preserved across the entire spectrum of the broadband mid-IR driver, these stretched pulses interfere with each other, giving rise to high-visibility fringes in the waveform of the transmitted mid-IR field (the right panel), with prominent echo field recurrences, observed at delay times 1/(cΔνP) and 1/(cΔνR) for the P and R rovibrational branches, respectively. Because the shape of these fringes is fully controlled by the spectrum of molecular rovibrational modes, all the information on a molecule encoded in absorption spectra can be retrieved from mid-IR pulse shapes, thus allowing molecular fingerprints to be read out through a careful analysis of mid-IR waveforms. (b) Dynamics of a dark wave: the envelope of a dark wave, Re[A(z,t) − A(0,t)], induced by interaction with a molecular transition with a Lorentzian lineshape with T2 = 30 ps and Δωl = 0 for αlz = 0.1 (pink line), 1 (green line), and 100 (navy line). The input laser profile has a Gaussian envelope and a pulse width of 160 fs. The spectral profiles of the real and imaginary parts n and κ of the complex refractive index  are shown in the inset.
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f1: (a) Time-domain spectral interferometry in the mid-infrared. When its central wavelength is tuned on resonance with a typical molecular rovibrational band, the mid-IR driver, due to its extremely large bandwidth, interacts with the entire manifold of rovibrational transitions, exciting a broadband rovibrational wave packet. As a part of this process, the energy is transferred from the mid-IR driver to molecular motion, giving rise to narrowband absorption features in the spectrum of mid-IR radiation at the frequencies of individual molecular modes, separated by spectral intervals ΔνP and ΔνR for the P and R rovibrational branches, respectively. In the time domain, these narrowband spectral dips translate into stretched dark field waveforms, as shown in the right panel. Due to the coherence preserved across the entire spectrum of the broadband mid-IR driver, these stretched pulses interfere with each other, giving rise to high-visibility fringes in the waveform of the transmitted mid-IR field (the right panel), with prominent echo field recurrences, observed at delay times 1/(cΔνP) and 1/(cΔνR) for the P and R rovibrational branches, respectively. Because the shape of these fringes is fully controlled by the spectrum of molecular rovibrational modes, all the information on a molecule encoded in absorption spectra can be retrieved from mid-IR pulse shapes, thus allowing molecular fingerprints to be read out through a careful analysis of mid-IR waveforms. (b) Dynamics of a dark wave: the envelope of a dark wave, Re[A(z,t) − A(0,t)], induced by interaction with a molecular transition with a Lorentzian lineshape with T2 = 30 ps and Δωl = 0 for αlz = 0.1 (pink line), 1 (green line), and 100 (navy line). The input laser profile has a Gaussian envelope and a pulse width of 160 fs. The spectral profiles of the real and imaginary parts n and κ of the complex refractive index are shown in the inset.

Mentions: Ultrashort waveforms with broadband coherent spectra in the mid-infrared play the central role in the time-domain technique for the detection and identification of molecular modes implemented in this work. When the central wavelength of such a waveform is tuned on resonance with a typical molecular rovibrational band, the mid-IR driver, due to its extremely large bandwidth, can interact with the entire manifold of rovibrational transitions, exciting a broadband rovibrational wave packet. As a part of this process, the energy is transferred from the mid-IR driver field to molecular motion, giving rise to narrowband absorption features in the spectrum of the mid-IR driver at the frequencies of individual molecular modes (Fig. 1a). In the time domain, these narrowband spectral dips translate into dark field waveforms (Fig. 1a), whose phase is shifted by π relative to the phase of the adjacent spectral components and whose duration is much longer than the duration of the incident ultrashort mid-IR driver (see the Methods section). Figure 1b illustrates the dynamics of one of such dark waveforms, produced by an idealized Lorentzian absorption line (see the Methods section for details). For short propagation paths, αlz ≪ 1, with αl being the absorption coefficient at the center of the line, the waveform has an exponentially decaying envelope (the dash--dotted line in Fig. 1b), as dictated by the Fourier transform of a Lorentzian spectrum. For longer propagation paths, however, propagation effects tend to distort this time-domain map of a molecular mode (see Fig. 1b and the Methods section), generally making it more difficult to retrieve the parameters of molecular motions from this dark waveform.


Time-domain spectroscopy in the mid-infrared.

Lanin AA, Voronin AA, Fedotov AB, Zheltikov AM - Sci Rep (2014)

(a) Time-domain spectral interferometry in the mid-infrared. When its central wavelength is tuned on resonance with a typical molecular rovibrational band, the mid-IR driver, due to its extremely large bandwidth, interacts with the entire manifold of rovibrational transitions, exciting a broadband rovibrational wave packet. As a part of this process, the energy is transferred from the mid-IR driver to molecular motion, giving rise to narrowband absorption features in the spectrum of mid-IR radiation at the frequencies of individual molecular modes, separated by spectral intervals ΔνP and ΔνR for the P and R rovibrational branches, respectively. In the time domain, these narrowband spectral dips translate into stretched dark field waveforms, as shown in the right panel. Due to the coherence preserved across the entire spectrum of the broadband mid-IR driver, these stretched pulses interfere with each other, giving rise to high-visibility fringes in the waveform of the transmitted mid-IR field (the right panel), with prominent echo field recurrences, observed at delay times 1/(cΔνP) and 1/(cΔνR) for the P and R rovibrational branches, respectively. Because the shape of these fringes is fully controlled by the spectrum of molecular rovibrational modes, all the information on a molecule encoded in absorption spectra can be retrieved from mid-IR pulse shapes, thus allowing molecular fingerprints to be read out through a careful analysis of mid-IR waveforms. (b) Dynamics of a dark wave: the envelope of a dark wave, Re[A(z,t) − A(0,t)], induced by interaction with a molecular transition with a Lorentzian lineshape with T2 = 30 ps and Δωl = 0 for αlz = 0.1 (pink line), 1 (green line), and 100 (navy line). The input laser profile has a Gaussian envelope and a pulse width of 160 fs. The spectral profiles of the real and imaginary parts n and κ of the complex refractive index  are shown in the inset.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
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f1: (a) Time-domain spectral interferometry in the mid-infrared. When its central wavelength is tuned on resonance with a typical molecular rovibrational band, the mid-IR driver, due to its extremely large bandwidth, interacts with the entire manifold of rovibrational transitions, exciting a broadband rovibrational wave packet. As a part of this process, the energy is transferred from the mid-IR driver to molecular motion, giving rise to narrowband absorption features in the spectrum of mid-IR radiation at the frequencies of individual molecular modes, separated by spectral intervals ΔνP and ΔνR for the P and R rovibrational branches, respectively. In the time domain, these narrowband spectral dips translate into stretched dark field waveforms, as shown in the right panel. Due to the coherence preserved across the entire spectrum of the broadband mid-IR driver, these stretched pulses interfere with each other, giving rise to high-visibility fringes in the waveform of the transmitted mid-IR field (the right panel), with prominent echo field recurrences, observed at delay times 1/(cΔνP) and 1/(cΔνR) for the P and R rovibrational branches, respectively. Because the shape of these fringes is fully controlled by the spectrum of molecular rovibrational modes, all the information on a molecule encoded in absorption spectra can be retrieved from mid-IR pulse shapes, thus allowing molecular fingerprints to be read out through a careful analysis of mid-IR waveforms. (b) Dynamics of a dark wave: the envelope of a dark wave, Re[A(z,t) − A(0,t)], induced by interaction with a molecular transition with a Lorentzian lineshape with T2 = 30 ps and Δωl = 0 for αlz = 0.1 (pink line), 1 (green line), and 100 (navy line). The input laser profile has a Gaussian envelope and a pulse width of 160 fs. The spectral profiles of the real and imaginary parts n and κ of the complex refractive index are shown in the inset.
Mentions: Ultrashort waveforms with broadband coherent spectra in the mid-infrared play the central role in the time-domain technique for the detection and identification of molecular modes implemented in this work. When the central wavelength of such a waveform is tuned on resonance with a typical molecular rovibrational band, the mid-IR driver, due to its extremely large bandwidth, can interact with the entire manifold of rovibrational transitions, exciting a broadband rovibrational wave packet. As a part of this process, the energy is transferred from the mid-IR driver field to molecular motion, giving rise to narrowband absorption features in the spectrum of the mid-IR driver at the frequencies of individual molecular modes (Fig. 1a). In the time domain, these narrowband spectral dips translate into dark field waveforms (Fig. 1a), whose phase is shifted by π relative to the phase of the adjacent spectral components and whose duration is much longer than the duration of the incident ultrashort mid-IR driver (see the Methods section). Figure 1b illustrates the dynamics of one of such dark waveforms, produced by an idealized Lorentzian absorption line (see the Methods section for details). For short propagation paths, αlz ≪ 1, with αl being the absorption coefficient at the center of the line, the waveform has an exponentially decaying envelope (the dash--dotted line in Fig. 1b), as dictated by the Fourier transform of a Lorentzian spectrum. For longer propagation paths, however, propagation effects tend to distort this time-domain map of a molecular mode (see Fig. 1b and the Methods section), generally making it more difficult to retrieve the parameters of molecular motions from this dark waveform.

Bottom Line: Here, we show that, with a combination of advanced ultrafast technologies and nonlinear-optical waveform characterization, time-domain techniques can be advantageously extended to the metrology of fundamental molecular motions in the mid-infrared.In our scheme, the spectral modulation of ultrashort mid-infrared pulses, induced by rovibrational motions of molecules, gives rise to interfering coherent dark waveforms in the time domain.These high-visibility interference patterns can be read out by cross-correlation frequency-resolved gating of the field in the visible generated through ultrabroadband four-wave mixing in a gas phase.

View Article: PubMed Central - PubMed

Affiliation: 1] Physics Department, International Laser Center, M.V. Lomonosov Moscow State University, Moscow 119992, Russia [2] Russian Quantum Center, ul. Novaya 100, Skolkovo, Moscow Region, 1430125 Russia.

ABSTRACT
When coupled to characteristic, fingerprint vibrational and rotational motions of molecules, an electromagnetic field with an appropriate frequency and waveform offers a highly sensitive, highly informative probe, enabling chemically specific studies on a broad class of systems in physics, chemistry, biology, geosciences, and medicine. The frequencies of these signature molecular modes, however, lie in a region where accurate spectroscopic measurements are extremely difficult because of the lack of efficient detectors and spectrometers. Here, we show that, with a combination of advanced ultrafast technologies and nonlinear-optical waveform characterization, time-domain techniques can be advantageously extended to the metrology of fundamental molecular motions in the mid-infrared. In our scheme, the spectral modulation of ultrashort mid-infrared pulses, induced by rovibrational motions of molecules, gives rise to interfering coherent dark waveforms in the time domain. These high-visibility interference patterns can be read out by cross-correlation frequency-resolved gating of the field in the visible generated through ultrabroadband four-wave mixing in a gas phase.

No MeSH data available.


Related in: MedlinePlus