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Efforts to discourage academic misconduct in online learning environments frequently include the use of remote proctoring services. While these services are relatively commonplace in undergraduate science courses, there are open questions about students’ remote assessment environments and their concerns related to remote proctoring services. Using a survey distributed to 11 undergraduate science courses engaging in remote instruction at three American, public, research-focused institutions during the spring of 2021, we found that the majority of undergraduate students reported testing in suboptimal environments. Students’ concerns about remote proctoring services were closely tied to technological difficulties, fear of being wrongfully accused of cheating, and negative impacts on mental health. Our results suggest that remote proctoring services can create and perpetuate inequitable assessment environments for students, and additional research is required to understand the efficacy of their intended purpose to prevent cheating. We also advocate for continued conversations about the broader social and institutional conditions that can pressure students into cheating. While changes to academic culture are difficult, these conversations are necessary for higher education to remain relevant in an increasingly technological world.

 

Vigorous efforts to harness the topological properties of light have enabled a multitude of novel applications. Translating the applications of structured light to higher spatial and temporal resolutions mandates their controlled generation, manipulation, and thorough characterization in the short-wavelength regime. Here, we resort to high-order harmonic generation (HHG) in a noble gas to upconvert near-infrared (IR) vector, vortex, and vector-vortex driving beams that are tailored, respectively, in their spin angular momentum (SAM), orbital angular momentum (OAM), and simultaneously in their SAM and OAM. We show that HHG enables the controlled generation of extreme-ultraviolet (EUV) vector beams exhibiting various spatially dependent polarization distributions, or EUV vortex beams with a highly twisted phase. Moreover, we demonstrate the generation of EUV vector-vortex beams (VVB) bearing combined characteristics of vector and vortex beams. We rely on EUV wavefront sensing to unambiguously affirm the topological charge scaling of the HHG beams with the harmonic order. Interestingly, our work shows that HHG allows for a synchronous controlled manipulation of SAM and OAM. These EUV structured beams bring in the promising scenario of their applications at nanometric spatial and sub-femtosecond temporal resolutions using a table-top harmonic source. 

Ultrafast laser pulse beams are four-dimensional, space–time phenomena that can exhibit complicated, coupled spatial and temporal profiles. Tailoring the spatiotemporal profile of an ultrafast pulse beam is necessary to optimize the focused intensity and to engineer exotic spatiotemporally shaped pulse beams. Here we demonstrate a single-pulse, reference-free spatiotemporal characterization technique based on two colocated synchronized measurements: (1) broadband single-shot ptychography and (2) single-shot frequency resolved optical gating. We apply the technique to measure the nonlinear propagation of an ultrafast pulse beam through a fused silica window. Our spatiotemporal characterization method represents a major contribution to the growing field of spatiotemporally engineered ultrafast laser pulse beams.

 

Much of our understanding of atmospheric circulation comes from relationships between aspects of the circulation and the mean state of the atmosphere. In particular, the concept of mean available potential energy (MAPE) has been used previously to relate the strength of the extratropical storm tracks to the zonal-mean temperature and humidity distributions. Here, we calculate for the first time the MAPE of the zonally varying (i.e., three-dimensional) time-mean state of the atmosphere including the effects of latent heating. We further calculate a local MAPE by restricting the domain to an assumed eddy size, and we partition this local MAPE into convective and nonconvective components. Local convective MAPE maximizes in the subtropics and midlatitudes, in many cases in regions of the world that are known to have intense convection. Local nonconvective MAPE has a spatial pattern similar to the Eady growth rate, although local nonconvective MAPE has the advantage that it takes into account latent heating. Furthermore, the maximum potential ascent associated with local nonconvective MAPE is related to the frequency of warm conveyor belts (WCBs), which are ascending airstreams in extratropical cyclones with large impacts on weather. This maximum potential ascent can be calculated based only on mean temperature and humidity, and WCBs tend to start in regions of high maximum potential ascent on a given day. These advances in the use of MAPE are expected to be helpful to connect changes in the mean state of the atmosphere, such as under global warming, to changes in important aspects of extratropical circulation. 

While there has been success in Wakefield acceleration of electrons, there are a number of applications that could benefit from acceleration to modest energy (~MeV) by the laser field, for example, ultrafast electron diffraction and injection into higher-energy laser-driven accelerators. Here we outline our scheme for ponderomotive acceleration of electrons (and in principle, positrons) in which we control the group velocity of ultrafast pulses through pulse front tilt. Provided the intensity is above the threshold for capture of electrons, the leading part of the pulse front effectively acts like a moving mirror whose shape is controlled by the spatio-temporal topology of the intensity profile. Our analytic models of the propagation of spatially-chirped beams, simple relativistic single-particle models of the laser-electron interaction and our implementation of these beams in particle-in-cell simulations help to predict the output electron energy and direction. We are preparing experiments on the ALEPH laser system at Colorado State University in which we will use the diagnostic techniques that we have developed to align our scaled-up design of a high-energy pulse compressor that will deliver spatially chirped pulses. 

We􀀁explore􀀁an􀀁electron􀀁acceleration􀀁scheme􀀁which􀀁uses􀀁the􀀁ponderomotive􀀁force􀀁of􀀁a􀀁tilted􀀁ultrafast􀀁laser􀀁as􀀁the􀀁drive􀀁mechanism􀀁for􀀁acceleration. The􀀁effect􀀁of􀀁pulse􀀁front􀀁curvature􀀁on􀀁the􀀁acceleration􀀁process􀀁is􀀁also􀀁discussed. 

The study of the physics of naturally occurring electrostatic discharges (ESDs) at early times is challenged by the difficulty in overcoming pre-trigger requirements of laser probes. In this work, ultraviolet (UV) pulses from a diode-pumped solid-state, Q-switched laser system are used to trigger ESDs. We use an open-air spark gap with a gap voltage held near threshold. The laser intensity is in the microjoule range so that seed electrons are produced through the photoelectric effect on the cathode. In contrast to laser-triggered spark gaps, the resulting discharges are anticipated to be very similar to those produced by random seed electrons. The triggering produces ESDs with a yield of >65%. While there is ~10ns jitter, co-recording of the current pulse will allow for time-resolved experimental diagnostics with ns timing resolution. Early results show a relatively short delay between triggering and the arc discharge (~100ns), indicating that collisional UV generation is a more likely source of secondary electrons than ion return current. Our experiment will be compared to our numerical models for plasma temperature and species evolution measurements in ESDs. Future experiments will be completed in a discharge chamber which allows for control of the gas composition and pressure. 

We introduce a self-referenced system that retrieves the full spatio-temporal profile of an ultrashort pulse using a Shack-Hartmann and second harmonic generation FROG. The key feature is the precise co-location of a spectral phase measurement at one spatial position with the spectrally resolved spatial measurements. 

We generalize our method for propagating spatially chirped Gaussian beams to properly calculate the evolution of geometric spectral phase through a lens. By expanding the spectral phase around the local central frequency, we analytically calculate the spatio-temporal field. Applications to intentionally detuned pulse compressors are discussed.