Spectrally resolved single-shot wavefront sensing of broadband high-harmonic sources

Wavefront sensors are an important tool to characterize coherent beams of extreme ultraviolet radiation. However, conventional Hartmann-type sensors do not allow for independent wavefront characterization of different spectral components that may be present in a beam, which limits their applicability for intrinsically broadband high-harmonic generation (HHG) sources. Here we introduce a wavefront sensor that measures the wavefronts of all the harmonics in a HHG beam in a single camera exposure. By replacing the mask apertures with transmission gratings at different orientations, we simultaneously detect harmonic wavefronts and spectra, and obtain sensitivity to spatiotemporal structure such as pulse front tilt as well. We demonstrate the capabilities of the sensor through a parallel measurement of the wavefronts of 9 harmonics in a wavelength range between 25 and 49 nm, with up to lambda/32 precision.Comment: 12 pages, 6 figure

Graduate Teaching Assistant Training: Preparing Instructors to Assist ESL Students in the Introductory Public Speaking Course

Much research identifies the need to assist English as a Second Language (ESL) students in our classrooms. Some communication educators have addressed this need by enrolling students in special sections of introductory courses for ESL students only. With a focus specifically on graduate teaching assistant (GTA) training, this paper suggests ways to assist ESL students, along with native speaking students, enrolled in regular sections of the introductory public speaking course. We first identify steps for assessing whether an ESL student is appropriately enrolled in a course. We then focus on ways instructors can assist ESL students with: 1) pronunciation, comprehensibility, and listening, 2) thinking rhetorically, and 3) delivery skills

ASPECT: A Survey to Assess Student Perspective of Engagement in an Active-Learning Classroom

This paper describes the development and validation of a survey to measure students? self-reported engagement during a wide variety of in-class active-learning exercises. The survey provides researchers and instructors alike with a tool to rapidly evaluate different active-learning strategies from the perspective of the learner

Second-Order Coherence Across the Brillouin Lasing Threshold

Brillouin-Mandelstam scattering is one of the most accessible nonlinear optical phenomena and has been widely studied since its theoretical discovery one hundred years ago. The scattering mechanism is a three-wave mixing process between two optical fields and one acoustic field and has found a broad range of applications spanning microscopy to ultra-narrow-linewidth lasers. Building on the success of utilizing this nonlinearity at a classical level, a rich avenue is now being opened to explore Brillouin scattering within the paradigm of quantum optics. Here, we take a key step in this direction by employing quantum optical techniques yet to be utilized for Brillouin scattering to characterize the second-order coherence of Stokes scattering across the Brillouin lasing threshold. We use a silica microsphere resonator and single-photon counters to observe the expected transition from bunched statistics of thermal light below the lasing threshold to Poissonian statistics of coherent light above the threshold. Notably, at powers approaching the lasing threshold, we also observe super-thermal statistics, which arise due to instability and a ``flickering'' in and out of lasing as the pump field is transiently depleted. The statistics observed across the transition, including the ``flickering'', are a result of the full nonlinear three-wave mixing process and cannot be captured by a linearized model. These measurements are in good agreement with numerical solutions of the three-wave Langevin equations and are well demarcated by analytical expressions for the instability and the lasing thresholds. These results demonstrate that applying second-order-coherence and photon-counting measurements to Brillouin scattering provides new methods to advance our understanding of Brillouin scattering itself and progress toward quantum-state preparation and characterization of acoustic modes.Comment: Main (8 pages, 2 figures) + Supplementary (6 pages, 1 figures), Submitte

Spectrally resolved wavefront characterization of broadband ultrafast high-harmonic pulses

We demonstrate a sensor that measures wavefronts of multiple extreme ultraviolet wavelengths simultaneously. By incorporating transmission gratings into the apertures of a Hartmann mask, we can record wavefront information for series of discrete harmonics from a high-harmonic generation source in a single camera exposure, without the need for scanning parts. Wavefronts of up to nine high harmonics at 25-49 nm wavelength are retrieved, and ultrafast spatiotemporal couplings can be detected

Spatially resolved Fourier transform spectroscopy in the extreme ultraviolet

Coherent extreme ultraviolet (XUV) radiation produced bytable-top high-harmonic generation (HHG) sources providesa wealth of possibilities in research areas ranging from attosecondphysics to high-resolution coherent diffractive imaging.However, it remains challenging to fully exploit the coherenceof such sources for interferometry and Fourier transform spectroscopy(FTS). This is due to the need for a measurementsystem that is stable at the level of a wavelength fraction, yetallows controlled scanning of time delays. Here, we demonstrateXUV interferometry and FTS in the 17–55 nm wavelengthrange using an ultrastable common-path interferometersuitable for high-intensity laser pulses that drive the HHGprocess. This approach enables the generation of fully coherentXUV pulse pairs with sub-attosecond timing variation, tunabletime delay, and a clean Gaussian spatial mode profile. Wedemonstrate the capabilities of our XUV interferometer byperforming spatially resolved FTS on a thin film composed oftitanium and silicon nitride

Spectrally resolved wavefront characterization of broadband ultrafast high-harmonic pulses

We demonstrate a sensor that measures wavefronts of multiple extreme ultraviolet wavelengths simultaneously. By incorporating transmission gratings into the apertures of a Hartmann mask, we can record wavefront information for series of discrete harmonics from a high-harmonic generation source in a single camera exposure, without the need for scanning parts. Wavefronts of up to nine high harmonics at 25-49 nm wavelength are retrieved, and ultrafast spatiotemporal couplings can be detected

Non-Gaussian mechanical motion via single and multi-phonon subtraction from a thermal state

Quantum optical measurement techniques offer a rich avenue for quantum control of mechanical oscillators via cavity optomechanics. In particular, a powerful yet little explored combination utilizes optical measurements to perform heralded non-Gaussian mechanical state preparation followed by tomography to determine the mechanical phase-space distribution. Here, we experimentally perform heralded single- and multi-phonon subtraction via photon counting to a laser-cooled mechanical thermal state with a Brillouin optomechanical system at room temperature, and use optical heterodyne detection to measure the s-parameterized Wigner distribution of the non-Gaussian mechanical states generated. The techniques developed here advance the state-of-the-art for optics-based tomography of mechanical states and will be useful for a broad range of applied and fundamental studies that utilize mechanical quantum-state engineering and tomography