Stefan Eggert

Direct sampling of electric-field vacuum fluctuations

Probing the fluctuating vacuum According to quantum mechanics, a vacuum is not empty space. A consequence of the uncertainly principle is that particles or energy can come into existence for a fleeting moment. Such vacuum or quantum fluctuations are known to exist, but evidence for them has been indirect. Riek et al. present an ultrafast optical based technique that probes the vacuum fluctuation of electromagnetic radiation directly. Science, this issue p. 420 Ultrafast optics can directly probe the electric-field vacuum fluctuations. The ground state of quantum systems is characterized by zero-point motion. This motion, in the form of vacuum fluctuations, is generally considered to be 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 inversely proportional to the four-dimensional space-time volume, which we sampled electro-optically with tightly focused laser pulses lasting a few femtoseconds. Subcycle 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 multiterahertz frequencies, such techniques might also allow time-resolved studies of intrinsic fluctuations of elementary excitations in condensed matter.

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

We experimentally demonstrate tunable, phase-matched difference frequency generation fully covering the spectral regime below 15 THz using 4H-SiC as nonlinear crystal. The material is also exploited as a broadband detector for electro-optic sampling.

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

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.

Single-cycle light pulses from a compact Er:fiber laser

We demonstrate a setup based entirely on compact Er:fiber technology which synthesizes pulses of a duration of 4.3 fs. This value corresponds to a single cycle of light in the telecom wavelength region.

Tunable Cr:Nd:GSGG lasers pumped by red diodes

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.

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

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

Generation of Single-Cycle Light Pulses with Compact Er:Fiber Technology

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

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

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.

Process for producing antireflection coatings

Based on a two-branch Er:fiber laser system we demonstrate the synthesis of 4.3 fs pulses, corresponding to single cycles of light in the telecom frequency band.