Ultrashort Laser Pulse Interaction With Photo-thermo-refractive Glass

Photo-thermo-refractive (PTR) glass is an ideal photosensitive material for recording phase volume holograms. It is a homogeneous multi-component silicate glass that demonstrates all the advantages of optical glass: thermal stability, high laser damage threshold, and a wide transparency range. Moreover the ability to record phase patterns (i.e. spatial refractive index variations) into PTR glass has resulted in the fabrication of volume holograms with diffraction efficiency greater than 99%. The conventional method of recording a hologram in PTR glass relies on exposure to continuous-wave ultraviolet laser radiation. In this dissertation the interaction between infrared ultrashort laser pulses and PTR glass is studied. It is shown that photosensitivity in PTR glass can be extended from the UV region to longer wavelengths (near-infrared) by exposure to ultrashort laser pulses. It is found that there exists a focusing geometry and laser pulse intensity interval for which photoionization and refractive index change in PTR glass after thermal development occur without laser-induced optical damage. Photoionization of PTR glass by IR ultrashort laser pulses is explained in terms of strong electric field ionization. This phenomenon is used to fabricate phase optical elements in PTR glass. The interaction between ultrashort laser pulses and volume holograms in PTR glass is studied in two laser intensity regimes. At intensities below ~10^12 W/cm^2 properties such as diffraction efficiency, angular divergence, selectivity, and pulse front tilt are shown to agree with the theory of linear diffraction for broad spectral width lasers. A volume grating pair arrangement is shown to correct the laser pulse distortions arising from pulse front tilt and angular divergence. At higher intensities of irradiation, nonlinear generation and diffraction of third harmonic is observed for three types of interactions: sum-frequency generation, front-surface THG generation, and THG due to phase-matching with a grating formed by modulation of the nonlinear refractive index of PTR glass

Process of production of high efficiency diffractive and refractive optical elements in multicomponent silicate glass by nonlinear photo ionization followed by thermal development.

Apparatus, methods and systems for production of high efficiency refractive and diffractive elements by providing a photo-sensitizer fi-ee multicomponent glass, exposing the multi component glass to pulsed laser radiation to produce refractive indexed modulation, and heating the exposed multicomponent silicate glass to produce the high efficiency refractive and diffractive elements. The pulsed laser radiation is infrared femtosecond pulses to ultraviolet nanosecond pulses which provide ionization of glass matrix. The multicomponent glass is a photosensitive glass with high transparency in ultraviolet spectral region, e.g. silicate glass which includes silver, fluorine and bromine and does not contain photosensitizers such as cerium and antimony, PTR glass, cerium free PTR glass and cerium + antimony free PTR glass

Nutiseadmete kasutamise profiilid loodusainete ja matemaatika õppimise kontekstis

Nutiseadmeid kasutatakse sageli igapäevaelus, kuid ei ole teada, mil viisil ja kui laialdaselt rakendatakse neid õppimise eesmärgil. Selle väljaselgitamiseks korraldati ülevaateuuring, milles osales 3521 õpilast 6. ja 9. klassist. DIGCOMPi raamistikust lähtudes hindasid õpilased, kui sageli nad kasutavad nutiseadmeid õppimiseks loodusainetes ja matemaatikas. Õpilased jagati hierarhilise klasteranalüüsi abil viide rühma: sünnipärased digikodanikud, infoinimesed, suhtlevad infoinimesed, loomeinimesed ja nutiseadmete mittekasutajad. Neist nelja esimese profiilid iseloomustavad eri viisil nutiseadmete kasutajaid, keda on kokku ligikaudu pool valimisse kuulunud õpilastest. Teise poole moodustavad nutiseadmete mittekasutajad, kelle seas saab eristada täpsemaid alarühmi (kokku 11). Alarühmade võrdlemine võimaldab kavandada viise, kuidas kujundada nutiseadmete kasutamise harjumust. Samuti ilmneb uurimistulemustest, et 6. ja 9. klassi õpilased ning poisid ja tüdrukud kuuluvad eri rühmadesse erineva tõenäosusega.  Summar

Koostöise probleemilahendamisoskuse kujundamine uurimuslikku õpet kasutades

Loodusainete tundides lahendatakse loodusteadusliku sisuga probleeme enamasti uurimuslike tegevustega. Uuringu eesmärk on selgitada välja, mis toetab õpilaste tulemuslikku koostööd uurimuslikes tegevustes, ja anda loodusainete õpetajatele soovitusi, kuidas integreerida koostöise probleemilahendamise oskuse ning aine- ja uurimuslike teadmiste kujundamist. Uuringus osalesid 7. klassi õpilased (N = 44), kellel tuli nutitelefoni kasutades virtuaallaboris kaaslasega koostööd teha. Tulemusi analüüsiti kvalitatiivselt deduktiivse sisuanalüüsi ja kvantitatiivselt Hesse jt (2015) raamistiku järgi. Uuring näitab, et õpilased viib tulemusliku koostööni õpetaja juhitud klassiarutelu. Õpilaste meelest aitavad koostöisele probleemilahendamisele kaasa katsetamine, mitme variandi läbiproovimine ning üksteisega suhtlemine. Õpilased vajavad täpseid juhiseid, et edukaks uurimuslikuks õppeks analüütiliselt mõelda, ülesanne uuesti läbi vaadata, teemaga seotud küsimusi esitada ja/või tõenditel põhinevalt teaduslikult arutleda. Summar

Why do students choose to study Information and Communications Technology?

Abstract It is a worldwide problem that although many students are highly interested in Information and Communications Technology (ICT), they do not study it at the higher education level, or if they do then many of them eventually dropout. We studied the reasons student candidates choose to study ICT, in order to gather data that can be used for improving future ICT recruitment and retention. During the admissions procedure to three higher education institutions in Estonia, 1,464 student candidates were asked what reasons influenced them to apply to Informatics or Information Technology. On average, 2.6 candidates competed per available position at the institutions. Qualitative content analysis was used to code the candidates' open-ended answers and resulted inductively in 14 distinguishable categories. The most frequent reasons for studying ICT were general interest in ICT, previous experience in the field, need for personal professional development, and importance of the field in the future. Interestingly, only a few candidates expressed as a reason the importance of high salaries. Chi-square analysis showed that candidates were accepted with higher probability if they found ICT to be suitable for them, or expressed good opportunities in the labour market. These results are useful for planning effective admission procedures to recruit ICT students

Assessing Students' Digital Literacy with Interactive Computer-Based Tasks Created in Google Apps Script

International audienceThis paper presents the development and testing of two interactive computer-based tasks for assessing aspects of students' digital literacy. The tasks were created using Google Apps Script to allow students to work with authentic digital productivity tools. Results from 156 university students indicate that the task requiring analysis of data in a spreadsheet application was significantly more difficult than the task requiring information literacy to make edits in a word processor application. These types of tasks offer more authentic ways for students to engage with digital technology during the assessment of their digital literacy. This study highlights the potential of Google Apps Scripts for developing and delivering tasks in performance-based assessments of students' digital literacy

Color Center Generation In Sodium-Calcium Silicate Glass By Nanosecond And Femtosecond Laser Pulses

It was found that high purity soda lime glass shows a markedly different induced absorption spectra when exposed to different types of ionizing radiation such as UV lamp or femtosecond and nanosecond laser pulses. The following irradiation was used in the experiments: nanosecond pulses at the fundamental and harmonics of a Nd:YAG laser (λ = 1064, 532, 355, and 266 nm), femtosecond pulses of a Ti:sapphire laser operating at λ = 780 nm, ultraviolet rays from a high pressure Xe lamp, X-rays, and Gamma rays. Features of radiation defect generations are discussed