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Register a new userTHz meta-foil - a new photonic material
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Seeing sharper or becoming invisible are visions strongly driving the development of THz metamaterials. Strings are a preferred architecture of metamaterials as they extend continuously along one dimension. Here, we demonstrate that laterally interconnecting strings by structural elements that are placed in oscillation nodes such as to not quench electromagnetic resonances enables manufacturing of self-supported free-standing all-metal metamaterials. Upright S-strings, interconnected by rods, form a space-grid which we call meta-foil. In this way, we introduce binding between the atoms of the metamaterial, thus doing away with conventional frozen-in solutions like matrix embedding or thin films on substrates. Meta-foils are locally stiff, yet globally flexible. Even bent to cylinders of 1 cm radius, they maintain their spectral response, thus becoming true metamaterials on curved surfaces. Exploiting UV/X-ray lithography and ultimately plastic moulding, meta-foils can be cost-effectively manufactured in large areas and quantities to serve as optical elements.
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Acquiring precise information about the mode content of a laser is critical for multiplexed optical communications, optical imaging with active wave-front control, and quantum-limited interferometric measurements. Hologram-based mode decomposition devices allow a fast, direct measurement of the mode content, but they have limited precision due to cross-coupling between modes. Here we report the first proof-of-principle demonstration of mode decomposition with a meta-surface, resulting in significantly enhanced precision. A mode-weight fluctuation of 0.6ppm (-62 dB) can be measured with 1 second of averaging at a Fourier frequency of 80 Hz, an improvement on the state-of-the-art by more than three orders of magnitude. The improvement is attributable to the reduction in cross-coupling enabled by the exceptional phase accuracy of the meta-surface. We show a systematic study of the limiting sources of noise, and we show that there is a promising path towards complete mode decomposition with similar precision.
Stacked layers of metal meshes embedded in a dielectric substrate are routinely used for providing spectral selection at THz frequencies. Recent work has shown that particular geometries allow the refractive index to be tuned to produce practical artificial materials. Here we show that by spatially grading in the plane of the mesh we can manufacture a Graded Index (GrIn) thin flat lens optimized for use at THz frequencies. Measurements on a prototype lens show we are able to obtain the parabolic profile of a Woods type lens which is dependent only on the mesh parameters. This technique could realize other exotic optical devices.
Femtosecond-scale ultrafast imaging is an essential tool for visualizing ultrafast dynamics in molecular biology, physical chemistry, atomic physics, and fluid dynamics. Pump-probe imaging and a streak camera are the most widely used techniques, but they are either demanding the repetitions of the same scene or sacrificing the number of imaging dimensions. Many interesting single-shot ultrafast imaging techniques have been developed in recent years for recording non-repetitive dynamic scenes. Nevertheless, there are still weaknesses in the number of frames, the number of image pixels, or spatial/temporal resolution. Here, we present a single-shot ultrafast microscopy that can capture more than a dozen frames at a time with the frame rate of 5 THz. We combine a spatial light modulator and a custom-made echelon for efficiently generating a large number of reference pulses with designed time delays and propagation angles. The single-shot recording of the interference image between these reference pulses with a sample pulse allows us to retrieve the stroboscopic images of the dynamic scene at the timing of the reference pulses. We demonstrated the recording of 14 temporal snapshots at a time, which is the largest to date, with the optimal temporal resolution set by the laser output pulse. Our ultrafast microscopy is highly scalable in the number of frames and temporal resolutions, and this will have profound impacts on uncovering the interesting spatio-temporal dynamics yet to be explored.
Laser-frequency stabilization with on-chip photonic integrated circuits will provide compact, low cost solutions to realize spectrally pure laser sources. Developing high-performance and scalable lasers is critical for applications including quantum photonics, precision navigation and timing, spectroscopy, and high-capacity fiber communications. We demonstrate a significant advance in compact, stabilized lasers to achieve a record low integral emission linewidth and precision carrier stabilization by combining integrated waveguide nonlinear Brillouin and ultra-low loss waveguide reference resonators. Using a pair of 56.4 Million quality factor (Q) Si$_3$N$_4$ waveguide ring-resonators, we reduce the free running Brillouin laser linewidth by over an order of magnitude to 330 Hz integral linewidth and stabilize the carrier to 6.5$times$10$^{-13}$ fractional frequency at 8 ms, reaching the cavity-intrinsic thermorefractive noise limit for frequencies down to 80 Hz. This work demonstrates the lowest linewidth and highest carrier stability achieved to date using planar, CMOS compatible photonic integrated resonators, to the best of our knowledge. These results pave the way to transfer stabilized laser technology from the tabletop to the chip-scale. This advance makes possible scaling the number of stabilized lasers and complexity of atomic and molecular experiments as well as reduced sensitivity to environmental disturbances and portable precision atomic, molecular and optical (AMO) solutions.
We describe an ultrafast time resolved pump-probe spectroscopy setup aimed at studying the switching of nanophotonic structures. Both fs pump and probe pulses can be independently tuned over broad frequency range between 3850 and 21050 cm$^{-1}$. A broad pump scan range allows a large optical penetration depth, while a broad probe scan range is crucial to study strongly photonic crystals. A new data acquisition method allows for sensitive pump-probe measurements, and corrects for fluctuations in probe intensity and pump stray light. We observe a tenfold improvement of the precision of the setup compared to laser fluctuations, allowing a measurement accuracy of better than $Delta$R= 0.07% in a 1 s measurement time. Demonstrations of the improved technique are presented for a bulk Si wafer, a 3D Si inverse opal photonic bandgap crystal, and z-scan measurements of the two-photon absorption coefficient of Si, GaAs, and the three-photon absorption coefficient of GaP in the infrared wavelength range.
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