Expectations and outcomes: How technologies drive virtual teaching

[EN] We evaluate the effectiveness of using Zoom for learning Modern Physics topics in a large engineering physics class at a land-grant university in Texas. This virtual technology challenged both students and professors. By implementing different approaches: providing ahead of the lectures reading assignments, PowerPoint presentations, and pre-recorded videos, during the class administering attendance mini-quizzes, and afterward, the assigning on WebAssign homework, elements of an effective class setting were introduced. Passion and mutual understanding united students and teachers to be stronger than the Covid-19 pandemic and to endure the challenging teaching environment. We describe some features of the technologies and the learning expectations. The evaluation of outcomes was done in two ways: quantitatively, by statistical measures, and qualitatively, through an anonymous student survey and a university-wide teacher evaluation.This work was supported by the Presidential Transformational Teaching Grant of Texas A&M University (PTTG 20) and by the Robert A. Welch Foundation Grant No. A1546.Schuessler, H.; Rodriguez, C.; Kolomenskii, A. (2021). Expectations and outcomes: How technologies drive virtual teaching. En 7th International Conference on Higher Education Advances (HEAd'21). Editorial Universitat Politècnica de València. 631-639. https://doi.org/10.4995/HEAd21.2021.12990OCS63163

High-power mid-infrared frequency comb source based on a femtosecond Er:fiber oscillator

We report on a high-power mid-infrared frequency comb source based on a femtosecond Er:fiber oscillator with a stabilized repetition rate at 250 MHz. The mid-infrared frequency comb is produced through difference frequency generation in a periodically poled MgO-doped lithium niobate crystal. The output power is about 120 mW with a pulse duration of about 80 fs, and spectrum coverage from 2.9 to 3.6 um. The coherence properties of the produced high-power broadband mid-infrared frequency comb are maintained, which was verified by heterodyne measurements. As the first application, the spectrum of a ~200 ppm methane-air mixture in a short 20 cm glass cell at ambient atmospheric pressure and temperature was measured.Comment: 3 pages, 5 figure

Intensity-Resolved Above Threshold Ionization of Xenon with Short Laser Pulses

We present intensity-resolved above threshold ionization (ATI) spectra of xenon using an intensity scanning and deconvolution technique. Experimental data were obtained with laser pulses of 58 fs and central wavelength of 800 nm from a chirped-pulse amplifier. Applying a deconvolution algorithm, we obtained spectra that have higher contrast and are in excellent agreement with characteristic 2 $U_p$ and 10 $U_p$ cutoff energies contrary to that found for raw data. The retrieved electron ionization probability is consistent with the presence of a second electron from double ionization. This recovered ionization probability is confirmed with a calculation based on the PPT tunneling ionization model [Perelomov, Popov, and Terent'ev, Sov. Phys. JETP 23, 924 (1966)]. Thus, the measurements of photoelectron yields and the proposed deconvolution technique allowed retrieval of more accurate spectroscopic information from the ATI spectra and ionization probability features that are usually concealed by volume averaging.Comment: 21 pages, 7 figure

Real-time dual frequency comb spectroscopy in the near infrared

We use two femtosecond Erbium-doped fiber lasers with slightly different repetition rates to perform a modern type of Fourier transform spectroscopy without moving parts. The measurements are done in real time, and it takes less than 50 microseconds. We work with somewhat different spectral outputs from two Erbium-doped fiber lasers and employ spectral filtering based on a 2f-2f grating setup to select the common spectral region of interest, thereby increasing the signal-to-noise ratio. The interferogram is taken with a 20 cm long gas cell, containing a mixture of acetylene and air at atmospheric pressure, and is fast-Fourier-transformed to obtain the broadband spectral fingerprint of the gas.Comment: 4 pages, 4 figure

Spontaneous Raman spectra of dipicolinic acid in microcrystalline form

Abstract. Dipicolinic acid (DPA) is an important component of bacterial spores. The Raman spectrum of DPA in the form of compacted powder was measured in reflection at room temperature with excitation by a nanosecond laser at 532 nm. The spectrum presents a set of characteristic frequency bands in the region 700-3090 cm À1 that were identified with characteristic vibrational modes of the DPA molecule

Laser-excited acoustic oscillations in silver and bismuth nanowires

Journals published by the American Physical Society can be found at http://journals.aps.org/Coherent acoustic oscillations in Bi and Ag nanowire samples were studied with a femtosecond pump-probe technique and detection of the scattered light. The observed optical and acoustic properties reflect the nanostructure of these materials. The electronic and lattice contributions to the excitation of coherent acoustic phonons are described using a two-temperature model. The excitation is performed at different laser fluences, and the high density of optically induced excitations modifies the state of the lattice. A transient state with softening of the lattice was observed in Ag nanowire samples

Avoided Crossing Patterns and Spectral Gaps of Surface Plasmon Modes in Gold Nano-Structures

The transmission of ultrashort (7 fs) broadband laser pulses through periodic gold nano-structures is studied. The distribution of the transmitted light intensity over wavelength and angle shows an efficient coupling of the incident p-polarized light to two counter-propagating surface plasmon (SP) modes. As a result of the mode interaction, the avoided crossing patterns exhibit energy and momentum gaps, which depend on the configuration of the nano-structure and the wavelength. Variations of the widths of the SP resonances and an abrupt change of the mode interaction in the vicinity of the avoided crossing region are observed. These features are explained by the model of two coupled modes and a coupling change due to switching from the high frequency dark mode to the low frequency bright mode for increasing wavelength of the excitation light. PACS numbers: 73.20.Mf, 42.70.Qs, 42.25.-p,Comment: 17 pages, 4 figure

Effect of circularly polarized femtosecond laser pulses on alignment dynamics of linear molecules observed by strong-field photoelectron yields

By measuring femtosecond laser driven strong-field electron yields for linear molecules aligned by circularly polarized femtosecond laser pulses, we study the rotational wavepacket evolution of N2, CO, and C2H2 gas molecules. We show that circular polarization produces a net alignment along the laser pulse propagation axis at certain phases of the evolution. This gives the possibility to control alignment of linear molecules outside the plane of polarization, which can provide new capabilities for molecular imaging. The experimental results were compared to the calculated field-free molecular alignment parameter taking into account the effects of electronic structure and symmetry of the molecules. By fitting the calculated impulsive alignment parameter to the measured experimental data we determined the molecular rotational constants of the linear gas molecules

Control of Femtosecond Filamentation by Revivals of Nonadiabatic Molecular Alignment

Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC) -- JUN 25-29, 2017 -- Munich, GERMANYKaya, Necati/0000-0001-9461-7623WOS: 000432564601271…NPRP award from the Qatar National Research Fund (a member of The Qatar Foundation) [NPRP 8-735-1-154]; Robert A. Welch FoundationThe Welch Foundation [A1546]This work was made possible by the NPRP award [NPRP 8-735-1-154] from the Qatar National Research Fund (a member of The Qatar Foundation) and Robert A. Welch Foundation (Grant No. A1546)