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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(More)
In this study, we report a minimal-cost and minimal-complexity Cr:LiSAF laser that is pumped only by one inexpensive single-spatial-mode diode. The pump diode, which was originally developed for DVD-writers, provides 130 mW of output power at 660 nm with an efficiency of 30%. This simple pump source enables the construction of a Cr:LiSAF laser that (i) has(More)
The advent of self-referenced opt' ical frequency combs,,2 has sparked the development of novel areas in ultrafast sciences such as attosecond technology3.4 and the synthesis of arbitrary optical waveforms s ,6. Few-cycle light pulses are key to these time-domain applications, driving a quest for reliable, stable and cost-efficient mode-locked laser sources(More)
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(More)
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