Ari Feldman

Ultra-low-noise monolithic mode-locked solid-state laser

Low-noise, high-repetition-rate mode-locked solid-state lasers are attractive for precision measurement and microwave generation, but the best lasers in terms of noise performance still consist of complex, bulky optical setups, which limits their range of applications. In this Letter, we present an approach for producing highly stable pulse trains with a record-low residual integrated offset frequency phase noise of 14 mrad at 1 GHz fundamental repetition rate using a monolithic mode-locked solid-state laser. The compact monolithic design simplifies implementation of the laser by fixing the cavity parameters and operates using just 265 mW of 980 nm pump light.

Portable, high-accuracy, non-absorbing laser power measurement at kilowatt levels by means of radiation pressure

We describe a non-traditional optical power meter which measures radiation pressure to accurately determine a lasers optical power output. This approach traces its calibration of the optical watt to the kilogram. Our power meter is designed for high-accuracy and portability with the capability of multi-kilowatt measurements whose upper power limit is constrained only by the mirror quality. We provide detailed uncertainty evaluation and validate experimentally an average expanded relative uncertainty of 0.016 from 1 kW to 10 kW. Radiation pressure as a power measurement tool is unique to the extent that it does not rely on absorption of the light to produce a high-accuracy result. This permits fast measurements, simplifies power scalability, and allows high-accuracy measurements to be made during use of the laser for other applications.

Equivalent isotropic response as a surrogate for incident field strength

The strength of an electromagnetic plane wave incident in the free field can be characterized in terms of power output by an idealized isotropic antenna probe. We refer to the parameter as equivalent isotropic incident power (EIIP), though it lacks an accepted name. This parameter has begun to enter use in various industry standards, technical reports, and peer-reviewed papers. To our knowledge, however, it has not been defined or studied in detail by prior work. We start to address this gap here with a proposed a definition, physical interpretation, and comparison to field strength.

Measurement Challenges for 5G and Beyond: An Update from the National Institute of Standards and Technology

In less than a decade since the mainstreaming of cellular wireless technology, spectrum has become saturated by data-intensive smartphones, driving the so-called spectrum crunch. As a solution, the wireless community is pursuing the use of alternatives to current wireless technologies, including multiple-input/multipleoutput (MIMO) antenna arrays that allow increased simultaneous transmission capacity; the millimeter-wave (mmW) spectrum (30-300 GHz) to alleviate the spectrum crunch in current frequency bands; and ultradense networks transmitting wide-band modulated signals to allow short-range, high-speed data transfer.

Monolithic device for modelocking and stabilization of frequency combs

We demonstrate a device that integrates a III-V semiconductor saturable absorber mirror with a graphene electro-optic modulator, which provides a monolithic solution to modelocking and noise suppression in a frequency comb. The device offers a pure loss modulation bandwidth exceeding 5 MHz and only requires a low voltage driver. This hybrid device provides not only compactness and simplicity in laser cavity design, but also small insertion loss, compared to the previous metallic-mirror-based modulators. We believe this work paves the way to portable and fieldable phase-coherent frequency combs.

Ultrafast photoconductive devices based upon GaAs:ErAs nanoparticle composite driven at 1550 nm

This paper reports progress on a type of ultrafast photoconductive source that can be driven at 1550 nm but exhibits the robustness of GaAs (e.g., low-temperature-grown GaAs) driven at 780 nm. The approach is GaAs doped heavily with Er (≈4x1020 cm-3 or 2% atomic-Er-to-Ga fraction) such that ErAs nanoparticles form spontaneously during epitaxial growth by MBE. The nanoparticles are mostly spherical with a diameter of a few nm while the packing density is estimated as high as ~2.2x1019/cm3. Yet, the Er-doped GaAs epilayer maintains excellent structural quality and smooth surface morphology. A photoconductive switch coupled to a 4-turn square spiral antenna is fabricated and characterized. At least ~40 μW average THz power is generated when the device is biased at 75 V and pumped with a 1550-nm 90-fs-short pulsed laser having average power ~85 mW. This research is significant for 1550-nm-technologycompatible, cost-effective THz sources.

Abrupt dependence of ultrafast extrinsic photoconductivity on Er fraction in GaAs:Er

We present a study of room-temperature, ultrafast photoconductivity associated with a strong, sub-bandgap, resonant absorption around λu2009=u20091550u2009nm in three MBE-grown GaAs epitaxial layers heavily doped with Er at concentrations of ≈2.9u2009×u20091018 (control sample), 4.4u2009×u20091020, and 8.8u2009×u20091020u2009cm−3, respectively. Transmission-electron microscopy reveals lack of nanoparticles in the control sample, but abundant in the other two samples in the 1.0-to-3.0-nm-diameter range, which is consistent with the previously known results. We measure very high photoelectron (Hall) mobility (2.57u2009×u2009103 cm2/V-s) and terahertz power (46u2009μW average) in the 4.4u2009×u20091020 sample, but then, an abrupt decay in these properties as well as the dark resistivity is seen as the Er doping is increased just 2 times. The Er doping has little effect on the picosecond-scale, 1550-nm photocarrier lifetime.

Optical amplitude and phase modulation dynamics at the single-photon level in a quantum dot ridge waveguide

The amplitude and phase of a materials nonlinear optical response provide insight into the underlying electronic dynamics that determine its optical properties. Phase-sensitive nonlinear spectroscopy techniques are widely implemented to explore these dynamics through demodulation of the complex optical signal field into its quadrature components; however, complete reconstruction of the optical response requires measuring both the amplitude and phase of each quadrature, which is often lost in standard detection methods. Here, we implement a heterodyne-detection scheme to fully reconstruct the amplitude and phase response of spectral hole-burning from InAs/GaAs charged quantum dots. We observe an ultra-narrow absorption profile and a corresponding dispersive lineshape of the phase, which reflect the nanosecond optical coherence time of the charged exciton transition. Simultaneously, the measurements are sensitive to electron spin relaxation dynamics on a millisecond timescale, as this manifests as a magnetic-field dependent delay of the amplitude and phase modulation. Appreciable amplitude modulation depth and nonlinear phase shift up to ~0.09×π radians (16°) are demonstrated, providing new possibilities for quadrature modulation at faint photon levels with several independent control parameters, including photon number, modulation frequency, detuning, and externally applied fields.The amplitude and phase of a materials nonlinear optical response provide insight into the underlying electronic dynamics that determine its optical properties. Phase-sensitive nonlinear spectroscopy techniques are widely implemented to explore these dynamics through demodulation of the complex optical signal field into its quadrature components; however, complete reconstruction of the optical response requires measuring both the amplitude and phase of each quadrature, which is often lost in standard detection methods. Here, we implement a heterodyne-detection scheme to fully reconstruct the amplitude and phase response of spectral hole-burning from InAs/GaAs charged quantum dots. We observe an ultra-narrow absorption profile and a corresponding dispersive lineshape of the phase, which reflect the nanosecond optical coherence time of the charged exciton transition. Simultaneously, the measurements are sensitive to electron spin relaxation dynamics on a millisecond timescale, as this manifests as a magnetic-field dependent delay of the amplitude and phase modulation. Appreciable amplitude modulation depth and nonlinear phase shift up to 0.09

Evolution of THz impulse imaging radar to 1550nm photoconductive switches

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Attosecond timing jitter characterization of mode-locked lasers using optical heterodyne techniques

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