Novel tools and techniques for electric-field-resolved investigations of ultrafast lightmatter interactions

Research group of PD Dr. Ioachim Pupeza

The optical electric fields associated with light-matter interactions carry in-depth information on the underlying physical mechanisms. The outstanding coherence of laser light enables direct measurements of these fields on their natural (sub-)femtosecond time scales, providing unique spectroscopy tools for a wide range of applications.

Our research primarily addresses the development of novel tools and techniques for field-resolved spectroscopy (FRS) of molecular vibrations in the IR spectral region, with a strong focus on label-free electric-field molecular fingerprinting of biological samples. However, the technologies and expertise developed in our group also impact on other fields, such as time- (and angle-) resolved photoelectron emission spectroscopy and microscopy (ARPES/PEEM) employing attosecond XUV pulses.

Field-resolved spectroscopy of molecular vibrations

Field-resolved spectroscopy of molecular vibrations: FRS records the coherent electric fields emitted by impulsively excited molecular vibrations. 

FRS records the coherent electric fields emitted by impulsively excited molecular vibrations.

a) waveform-stable few-cycle infrared pulses

At heart of our experimental setups lies the generation of few-cycle, high-power, waveform-stable infrared pulses. We target high pulse repetition rates (> 10 MHz) affording short measurement times and, thus, improved statistics. Our IR radiation sources are based on intra-pulse difference-frequency generation driven by the ultrashort near-IR pulses of state-of-the-art Yb-thin-disk oscillators [1,2] and fiber lasers [3,4], and have reached world records in terms of brilliance for broadband coherent sources.

Further development envisages the coverage of the entire molecular fingerprint region with powerful, few-cycle pulses. In close collaboration with the HFS and CMF groups, we work on the development of a new generation compact, broadband, coherent IR sources based on Cr:ZnS modelocked oscillators.

[1] High-power sub-two-cycle mid-infrared pulses at 100 MHz repetition rate

I. Pupeza, D. Sánchez, J. Zhang, N. Lilienfein, M. Seidel, O. Pronin, N. Karpowicz, T. Paasch-Colberg, I. Znakovskaya, V. Pervak, E. Fill, Z. Wei, F. Krausz, A. Apolonski & J. Biegert

Nature Photonics 9, 721 (2015)

[2] Field-resolved infrared spectroscopy of biological systems

I. Pupeza, M. Huber, M. Trubetskov, W. Schweinberger, S.A. Hussain, C. Hofer, K. Fritsch, M. Poetzlberger, L. Vamos, E. Fill, T. Amotchkina, K.V. Kepesidis, A. Apolonski, N. Karpowicz, V. Pervak, O. Pronin, F. Fleischmann, A. Azzeer, M. Zigman & F. Krausz

Nature 577, 52 (2020)

[3] Watt-scale 50-MHz source of single-cycle waveform-stable pulses in the molecular fingerprint region

T.P. Butler, D. Gerz, C. Hofer, J. Xu, C. Gaida, T. Heuermann, M. Gebhardt, L. Vamos, W. Schweinberger, J. Gessner, T. Siefke, M. Heusinger, U.D. Zeitner, A. Apolonski, N. Karpowicz, J. Limpert, F. Krausz, I. Pupeza

Optics Letters 44, 1730 (2019)

[4] Multi-octave spanning, Watt-level ultrafast mid-infrared source

T. Butler, N. Lilienfein, J. Xu, N. Nagl, C. Hofer, D. Gerz, K.F. Mak, C. Gaida, T. Heuermann, M. Gebhardt, J. Limpert, F. Krausz, I. Pupeza

Journal of Physics: Photonics 1, 044006 (2019)

b) impulsively-interrogated electric-field molecular fingerprints

The excitation of molecular vibrations is confined in time to the few optical cycles of the initial IR pulse. In the wake of this nearly impulsive excitation, the molecules emit a coherent wave, the electric-field molecular fingerprint (EMF), which is directly recorded in the time domain via electro-optic sampling. The shorter the excitation, the better the temporal separation of the EMF. This separation mitigates detection sensitivity limitations related to technical noise of the excitation and relaxes the (linear) dynamic range requirements to the detectors [1]. Harnessing these advantages, our prototypical FRS instrument has recently enabled the highest sensitivities for aqueous biological samples [1].

In addition, measuring molecular signals proportional to the electric field rather than the intensity permits, for the first time, broadband IR transmission measurements of aqueous samples as thick as 0.1 mm or more with high signal-to-noise ratio [2], opening the door to, e.g., IR vibrational fingerprinting of live cells with high throughput and of biological tissue.

[1] Field-resolved infrared spectroscopy of biological systems

I. Pupeza, M. Huber, M. Trubetskov, W. Schweinberger, S.A. Hussain, C. Hofer, K. Fritsch, M. Poetzlberger, L. Vamos, E. Fill, T. Amotchkina, K.V. Kepesidis, A. Apolonski, N. Karpowicz, V. Pervak, O. Pronin, F. Fleischmann, A. Azzeer, M. Zigman & F. Krausz

Nature 577, 52 (2020)

[2] Optimum sample thickness for trace analyte detection with field-resolved infrared spectroscopy

M. Huber, M. Trubetskov, S.A. Hussain, W. Schweinberger, C. Hofer & I. Pupeza

Analytical Chemistry 92, 7508 (2020)

c) electro-optic sampling with multi-Watt gate pulses

The optical waveforms associated with the light-matter interaction are measured via electro-optic sampling (EOS) involving their nonlinear mixing with an ultrashort gate pulse in a crystal. Our group has pioneered EOS with powerful, short-wave mid-IR gate pulses [1]. This enables record photon detection efficiencies of > 1% in a bandwidth spanning more than one octave in the molecular fingerprint region. Because the electric-field strength scales with the square root of the number of photons, this implies an unprecedented measurement sensitivity of within one order of magnitude from the ultimate limit for – potentially single-cycle – optical electric fields.

Further research targets the extension of this outstanding sensitivity to the entire molecular fingerprint region.

[1] Mid-infrared electric field sampling approaching single-photon sensitivity

C. Hofer, D. Gerz, M. Högner, T.P. Butler, C. Gaida, T. Heuermann, M. Gebhardt, N. Karpowicz, J. Limpert, F. Krausz & I. Pupeza

EPJ Web Conf. 243, 16001 (2020).

d) sub-attosecond-precision waveform metrology

Employing ultra-sensitive electro-optic sampling (EOS), we have characterized the phase stability of few-cycle pulses obtained via intra-pulse difference-frequency generation (IPDFG), obtaining sub-attosecond jitter for the zero crossings of thousands of consecutive waveforms (corresponding to pulse trains with sub-mrad carrier-envelope phase jitter) [1].

On one hand, this confirms the exquisite stability of IPDFG waveforms to an unprecedently high level. On the other hand, it establishes EOS as a broadband – both in the optical and radio-frequency ranges – measurement technique for the stability of optical waveforms.

We are currently working on harnessing this combination of IPDFG and EOS for zeptosecond-precision measurements of IR waves emerging from linear and, prospectively, nonlinear light-matter interactions.

[1] Train of Ultrashort Mid-Infrared Pulses with Sub-mrad Carrier-Envelope Phase Stability

S.A. Hussain, W. Schweinberger, T. Buberl, C. Hofer & I. Pupeza

in 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) (IEEE, 2019)

 

The proximity to several research groups at Attoworld guarantees strong research synergies as well as the immediate application of our techniques.

broadband infrared diagnostics
high-repetition femtosecond sources
ultrafast x-ray physics

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