2021, Sulzer, Philipp, Hagner, Matthias, Liehl, Andreas, Cimander, Moritz, Kempf, Hannes, Bitzer, Annegret, Herter, Alexa, Leitenstorfer, Alfred

Minimizing losses and suppression of reflection-induced echos in thin nonlinear crystals is of critical importance to both classical time-domain spectroscopy and time-domain quantum electrodynamics [1] . GaSe represents an important material in this context. However, it is challenging to coat and manipulate using macroscopic methods due to its van-der-Waals-bonded structure of hexagonal monolayers and atomically flat surfaces. At least, some progress relying on femtosecond laser ablation was demonstrated recently [2] .

2019, Liehl, Andreas, Sulzer, Philipp, Fehrenbacher, David, Seletskiy, Denis V., Leitenstorfer, Alfred

Phase noise in mode-locked Er:fiber systems shows strong spectral correlations emerging from broadband nonlinear-optical processes. Our fundamental insights are key to maximize the quality of passively phase-stable frequency combs and single-cycle pulse trains.

2017, Seletskiy, Denis V., Riek, Claudius, Sulzer, Philipp, Leitenstorfer, Alfred

Quantum field theory offers the most exact description of the physics of microscopic interactions. The process of field quantization necessitates the existence of a vacuum field with a corresponding zero-point energy [1]. From this point of view, the ability to directly measure and manipulate electrodynamic quantum vacuum field is an attractive prospect for experimental physics. It is bound to shed new light on the processes governing macroscopic properties of quantum matter [2,3] as well as to motivate table-top investigations of fundamental constituents of the quantum fields and their intrinsic connections the structure of spacetime [4,5].

2015, Seletskiy, Denis V., Fehrenbacher, David, Sulzer, Philipp, Leitenstorfer, Alfred

Modern precision metrology ever more strongly relies on the availability of optical frequency combs. We review our approach to passive stabilization of the carrier envelope phase (CEP) of a pulse train at full repetition rate via difference frequency generation. Using this approach, we demonstrate a inherently offset-free Er:fiber comb directly locked onto an optical reference ( 85 Rb) together with a possibility of an actively narrowed sub-500 mHz linewidth. This performance highlights an attractive potential of robust all-fiber comb systems toward applications in ultrahigh-precision metrology.

2019-03-07, Shestaev, Evgeny, Gaida, Christian, Heuermann, Tobias, Gebhardt, Martin, Butler, Thomas, Gerz, Daniel, Lilienfein, Nikolai, Sulzer, Philipp, Fischer, Marc, Leitenstorfer, Alfred, Limpert, Jens

Frequency combs are an enabling technology for metrology and spectroscopic applications in fundamental and life sciences. While frequency combs in the 1 μm regime, produced from Yb-based systems have already exceeded the 100 W – level, high power coverage of the interesting mid-infrared wavelength range remains yet to be demonstrated. Tm- and Ho-doped laser systems have recently shown operation at high average power levels in the 2 μm wavelength regime. However, frequency combs in this wavelength range have not exceeded the 5 W-average power level. In this work, we present a high power frequency comb, delivered by a Tm-doped chirped-pulse amplifier with subsequent nonlinear pulse compression. With an integrated phase noise of <320 mrad, low relative intensity noise of <0.5% and an average power of 60 W at 100 MHz repetition rate (and <30 fs FWHM pulse duration), this system demonstrates high stability and broad spectral coverage at an unrivalled average power level in this wavelength regime. Therefore, this laser will enable metrology and spectroscopy with unprecedented sensitivity and acquisition time. It is our ongoing effort to extend the spectral coverage of this system through the utilization of parametric frequency conversion into the mid-IR, thus ultimately enabling high power fingerprint spectroscopy in the entire molecular fingerprint region (2 – 20 μm).

2017, Liehl, Andreas, Fehrenbacher, David, Sulzer, Philipp, Seletskiy, Denis V., Leitenstorfer, Alfred

Applications of optical frequency combs in high precision metrology [1] require low-noise stabilization of its carrier-envelope offset (CEO) frequency. This task is commonly achieved via active feedback. Fully passive elimination of the CEO frequency based on difference frequency generation (DFG) between two octave-separated comb sections followed by amplification of the DFG signal in the EDFA has been demonstrated recently in an all-fiber design [2]. In this work, we develop a novel broadband characterization method of carrier-envelope phase (CEP) noise and apply it to study the passively phase-locked 100 MHz Er:fiber comb [3].

2016, Riek, Claudius, Sulzer, Philipp, Seeger, Maximillian, Seletskiy, Denis V., Leitenstorfer, Alfred

We generate few-cycle nonclassical transients by optical rectification of femtosecond pulses and subsequent index modulation in the multi-THz range. Subcycle analysis of quantum statistics by ultrabroadband electro-optic sampling reveals substantial squeezing below the vacuum level.

2019, Sulzer, Philipp, Liehl, Andreas, Keller, Kilian R., Huster, Jeldrik, Beckh, Cornelius, Leitenstorfer, Alfred

Amplitude fluctuations of pump pulses for frequency broadening by third-order processes are found to result in strong anti-correlations of spectral output components. We exploit this information to minimize intensity noise in subsequent nonlinear conversion steps.

2017, Liehl, Andreas, Fehrenbacher, David, Sulzer, Philipp, Seletskiy, Denis V., Leitenstorfer, Alfred

We study the carrier-envelope phase noise of an Er:fiber frequency comb which is passively phase-locked at the full repetition rate of 100 MHz. A novel characterization method determines an out-of-loop phase jitter of only 250 mrad when integrated over 12 orders of magnitude: from 50 μHz up to the Nyquist frequency.

2016, Riek, Claudius, Sulzer, Philipp, Seeger, Maximillian, Seletskiy, Denis V., Leitenstorfer, Alfred

We directly detect the multi-terahertz vacuum field and analyze its dependence on the probed space-time volume. A scheme for sensing the time derivative of the field enables timedomain quantum tomography with simultaneous sampling of both quadratures.