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Second-harmonic generation (SHG) in PPKTP, PPMgSLT, and PPMgLN crystals is analyzed by frequency-doubling CW light from a 1064 nm fiber laser over a range of powers up to 10 W. Data for fundamental powers less than 3 W is used to determine the effects of the fundamental laser linewidth on SHG and to identify imperfections in the periodicity and boundary sharpness of the crystals' poled domains which can reduce SHG. Data for fundamental powers greater than 3 W is used to diagnose and model limiting effects on SHG such as pump depletion and thermal dephasing. Thermal dephasing was found to reduce second-harmonic power by 25% or more for input fundamental powers approaching 10 W.

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Recent improvements to a source of electron-spin-polarized He+4 ions based on an optically pumped, rf-excited helium discharge are described that have resulted in ion polarizations P+ of ∼0.18 at currents of ∼1 nA and in an increase of over an order of magnitude in the quality factor P+2I.

We examine how student aptitudes impact how much students learn from doing graded online and written homework in an introductory electricity and magnetism course. Our analysis examines the correlation between successful homework completion rates and exam performance as well as how changes in homework completion correlate with changes in exam scores for students with different physics aptitudes. On average, successfully completing many homework problems correlated to better exam scores only for students with high physics aptitude. On the other hand, all other students showed zero or even a negative correlation between successful homework completion and exam performance. Low-and medium-aptitude students who did more homework did no better and sometimes scored lower on exams than their low-and medium-aptitude peers who did less homework. Our work also shows that long-term changes in homework completion correlated to long-term changes in exam scores only for students with high physics aptitude, but not for students with medium or low aptitude. We offer several explanations for the disparity in homework learning gains, including cognitive load theory, ineffective homework strategies, and various mismatches between homework and exams. Several solutions are proposed to address these possible deficiencies in graded online and written homework.