Eggert, Stefan

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Eggert
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Stefan
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Broadband analysis and self-control of spectral fluctuations in a passively phase-stable Er-doped fiber frequency comb

2020-02-03, Liehl, Andreas, Sulzer, Philipp, Fehrenbacher, David, Eggert, Stefan, Ludwig, Markus, Ritzkowsky, Felix, Seletskiy, Denis V., Leitenstorfer, Alfred

Carrier-envelope and optical phase noise of a femtosecond frequency comb based on Er-doped fiber technology is investigated and minimized without exploiting active external references. Ultrabroadband, coherent, and tailorable supercontinua are generated in a highly nonlinear germanosilicate fiber assembly. Difference frequency mixing between comb modes in their spectral extrema passively eliminates the carrier-envelope phase slip. This step generates an inherently offset-free comb with a relative frequency stability better than 10−21. In contrast, the phase fluctuations at the carrier frequency of 193 THz are increased as compared to the fundamental comb. Their level matches the value found by parabolic extrapolation of the phase noise of the fundamental comb to zero frequency. The latter is unambiguously accessible by means of any beat note centered at the carrier-envelope offset frequency. All these findings rely on strong correlations between the comb modes that are quantitatively described by an elastic tape model, underlining the deterministic character of the processes involved. The superior optical phase noise of the fundamental comb is transferred to the difference-frequency comb while not compromising the inherent cancellation of the carrier-envelope offset frequency. In this way, the optical linewidth of the passively phase-locked comb is reduced from 100 kHz to a measured value of 5 kHz, which is limited by the cw laser reference used for out-of-loop characterization.

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Tunable Cr:Nd:GSGG Lasers Pumped by Red Diodes

2017, Demirbas, Umit, Yerebakan, Talha, Eggert, Stefan, Bertram, Rainer, Reiche, Peter, Leitenstorfer, Alfred

Laser operation of Nd+3-doped gadolinium scandium gallium garnet (Nd:GSGG) has been first shown by Kaminskii et al. in 1976 [1]. In earlier studies, flaslamp or solar pumping of Nd:GSGG has been explored, and narrow absorption bands of the Nd+3 ion, that overlaps poorly with these broadband emitters resulted in low laser efficiencies. As a solution, co-doping with chromium ion (Cr:Nd:GSGG) has been applied to generate additional broad absorption bands in the visible to improve the absorption as well as the laser efficiency [2-3]. With the development of semiconductor technology, laser diode pumping has become the dominant excitation scheme for Nd-based laser systems [4-6]. Usually, laser diodes at the sharp absorption peaks of Nd:GSSG around 808 nm or 883 nm have been employed [4-5]. As an alternative, Cr co-doped samples provide broad absorption bands around 645 nm, in a spectral region where low cost laser diodes also exist [6]. While using these broad absorption bands, thermal control of the diode junction temperature, narrowband diode operation, and careful selection of diode central wavelength is not required. However, the quantum defect is higher, lowering the laser efficiencies.

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Compact and efficient Cr:LiSAF lasers pumped by one single-spatial-mode diode : a minimal cost approach

2012, Demirbas, Umit, Eggert, Stefan, Leitenstorfer, Alfred

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Coherent field transients below 15  THz from phase-matched difference frequency generation in 4H-SiC

2017-07-15, Fischer, Marco P., Bühler, Johannes, Fitzky, Gabriel, Kurihara, Takayuki, Eggert, Stefan, Leitenstorfer, Alfred, Brida, Daniele

We experimentally demonstrate tunable, phase-matched difference frequency generation covering the spectral region below 15 THz using 4H-SiC as a nonlinear crystal. This material combines a non-centrosymmetric lattice and strong birefringence with broadband transparency at low optical frequencies. Thorough refractive index measurements in the terahertz spectral range allow us to calculate phase-matching conditions for any near-infrared pump laser source. 4H-SiC is also exploited as a detector crystal for electro-optic sampling. The results allow us to estimate the effective second-order nonlinear coefficient.

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Direct sampling of electric-field vacuum fluctuations

2015-10-23, Riek, Claudius, Seletskiy, Denis V., Moskalenko, Andrey S., Schmidt, Jan, Krauspe, Philipp, Eckart, Sebastian, Eggert, Stefan, Burkard, Guido, Leitenstorfer, Alfred

The ground state of quantum systems is characterized by zero-point motion. Those vacuum fluctuations are generally deemed an elusive phenomenon that manifests itself only indirectly. Here, we report direct detection of the vacuum fluctuations of electromagnetic radiation in free space. The ground-state electric field variance is found to be inversely proportional to the four-dimensional space-time volume sampled electro-optically with tightly focused few-femtosecond laser pulses. Sub-cycle temporal readout and nonlinear coupling far from resonance provide signals from purely virtual photons without amplification. Our findings enable an extreme time-domain approach to quantum physics with nondestructive access to the quantum state of light. Operating at multi-terahertz frequencies, such techniques might also allow time-resolved studies of intrinsic fluctuations of elementary excitations in condensed matter.

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Synthesis of a single cycle of light with compact erbium-doped fibre technology

2010, Krauss, Günther, Lohss, Sebastian, Hanke, Tobias, Sell, Alexander, Eggert, Stefan, Huber, Rupert, Leitenstorfer, Alfred

The advent of self-referenced optical frequency combs has sparked the development of novel areas in ultrafast sciences such as attosecond technology and the synthesis of arbitrary optical waveforms. Few-cycle light pulses are key to these time-domain applications, driving a quest for reliable, stable and cost-efficient mode-locked laser sources with ultrahigh spectral bandwidth. Here, we present a set-up based entirely on compact erbium-doped fibre technology, which produces single cycles of light. The pulse duration of 4.3 fs is close to the shortest possible value for a data bit of information transmitted in the near-infrared regime. These results demonstrate that fundamental limits for optical telecommunications are accessible with existing fibre technology and standard free-space components.

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Red-diode-pumped Cr:Nd:GSGG laser : two-color mode-locked operation

2017-05-01, Yerebakan, Talha, Demirbas, Umit, Eggert, Stefan, Bertram, Rainer, Reiche, Peter, Leitenstorfer, Alfred

We have investigated in detail the continuous-wave (cw) and mode-locked performance of a diode-pumped Cr:Nd:GSGG laser. State-of-the-art single-mode and multimode laser diodes around 665 nm were used as pump sources. In cw operation, we have demonstrated lasing thresholds as low as 14 mW, slope efficiencies as high as 23.4%, and output powers up to 738 mW. The free running emission wavelength was 1061 nm. Lasing could also be obtained at 1051, 1058, 1065, 1068, 1072, 1103, and 1111 nm lines. A saturable Bragg reflector was used to initiate and sustain mode-locking where the Cr:Nd:GSGG laser produced 6-ps-long pulses around 1061 nm with an average power of 160 mW. The repetition rate was 142.65 MHz, resulting in pulse energies of 1.1 nJ and peak powers of 175 W. An off-surface optical axis quartz birefringent filter (BRF) was inserted inside the laser cavity at Brewster’s angle to obtain two-color cw and mode-locked laser operation at the 1051 and 1058 nm and 1058 and 1061 transition pairs, resulting in cw powers up to 60 mW and cw mode-locked average powers up to 45 mW. Unlike many other methods applied for two-color mode-locked laser operation, usage of the BRF enabled regulation of the ratio of the power in each line by fine adjustment of its rotation angle. The method could potentially be used for other gain media as well, which could simplify development of multicolor solid-state laser systems.

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Compact and efficient Cr:LiSAF laser pumped by one low-cost single-spatial-mode diode

2012-06-01, Demirbas, Umit, Eggert, Stefan, Leitenstorfer, Alfred

We present a minimal-cost Cr:LiSAF laser that is pumped by one single-spatial-mode diode. The pumping system (diode, diode driver, and the diode holder) has a total cost of about $500 and provided 130 mW of diffraction-limited pump power around 660 nm. The entire Cr:LiSAF laser system has an estimated total material cost below $5k, a footprint of about 20 cm × 35 cm, does not require cooling and can be driven by batteries, making the system ideal for applications that require portability. In continuous wave (cw) laser experiments, we have demonstrated lasing thresholds as low as 2 mW, slope efficiencies as high as 52%, output powers up to 58 mW, and a record tuning range extending from 780 nm to 1110 nm. In cw mode-locked operation, using a 0.5% output coupler, 100-fs pulses with an average power of 38 mW, and with an optical spectrum centered around 865 nm have been obtained at a repetition rate of 235 MHz. With a more compact cavity and using a 0.1% output coupler, 70-fs pulses with an average power of 20 mW have been obtained at a repetition rate of 509 MHz. We believe that this portable, minimal cost Cr:LiSAF laser system might be an attractive source for applications like amplifier seeding that do not require high average output power levels.