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

Photoionization Of Wide Bandgap Silicate Glasses By Ultrashort Ir Laser Pulses

We study the excitation of luminescence, photoionization, and laser-induced breakdown in a multi-component silicate photo-thermo-refractive (PTR) glass, and in fused silica. PTR glass is a high-purity homogeneous photosensitive alkali-silicate glass with intrinsic absorption edge at 5.8 eV (214 nm). Experiments are conducted with ultrashort laser pulses (100 fsec\u3c τ \u3c 1.5 psec) at the wavelengths 780 nm, 1430 nm, and 1550 nm. Filaments are observed inside both glasses and explained by a balance between Kerr self-focusing and free electron defocusing. Keldysh theory is used to model the formation of filaments and values of about 10 13 W/cm 2 for laser intensity and 10 19 cm -3 for free-electron density are estimated. Laser-induced damage by pulses at 1430 nm and 1550 nm is detected in fused silica and PTR glass by third harmonic generation due to the formation of an interface between a damage site and the surrounding glass matrix. It is found that there is an intensity range where luminescence and photoionization in both glasses occurs without laser-induced damage. © 2008 SPIE

Nonlinear Photosensitivity Of Photo-Thermo-Refractive Glass By High Intensity Laser Irradiation

Photo-thermo-refractive (PTR) glass is a material for high-efficiency phase volume hologram recording which possesses linear photosensitivity in the near UV region from 280 to 350 nm. In this paper nonlinear photosensitivity by 355 nm nanosecond pulses with intensity exceeding 1 MW/cm2 and by 783 nm femtosecond pulses with intensity exceeding 1 TW/cm2 is demonstrated. No photo-sensitizers are necessary in PTR glass for nonlinear photosensitivity. Photosensitivity by 355 nm nanosecond pulses is determined by glass matrix ionization resulting from two-photon absorption of incident radiation by glass matrix. Photosensitivity by 783 nm femtosecond pulses is determined by glass matrix ionization from nonlinear interaction of fundamental radiation and supercontinuum with modified glass matrix due to strong electric fields of incident radiation. © 2008 Elsevier B.V. All rights reserved

Phase Fresnel Lens Recorded In Photo-Thermo-Refractive Glass By Selective Exposure To Infrared Ultrashort Laser Pulses

Anew two-step approach for fabricating phase optical elements in photo-thermo-refractive glass by exposure to IR ultrashort laser pulses followed by thermal development is shown. A binary phase Fresnel lens was designed to focus light at 632.8 nm to a focal length of 400 cm. Conditions of ultrashort pulse irradiation and thermal development were chosen to achieve π phase shift between zone boundaries. The focusing efficiency of the element was measured to be close to 50%. © 2008 Optical Society of America

Ultrashort laser pulse diffraction by transmitting volume Bragg gratings in photo-thermo-refractive glass

We report on the characteristics of ultrashort laser pulse diffraction by transmitting volume Bragg gratings recorded in photo-thermo-refractive glass. The angular and spectral selectivity properties of these phase volume gratings are shown to obey the predictions of a modified Kogelnik's coupled wave analysis that accounts for polychromatic beams. Spatio-temporal distortions such as angular dispersion and pulse front tilt that occur after diffraction by a single volume grating are studied and corrected by using a volume grating pair. The angular filtering properties of volume gratings offer potential as spatial filtering elements inside ultrafast laser cavities

Non-collinear generation of third harmonic of IR ultrashort laser pulses by PTR glass volume Bragg gratings

Three conditions for non-collinear third harmonic generation by a PTR glass volume Bragg grating are demonstrated using infrared ultrashort pulse illumination. Each condition corresponds to a different angle of grating orientation and a separate generation mechanism. We identify the mechanisms as corresponding to sum-frequency generation, Bragg diffraction of 3 omega, and a non-resonant Bragg condition involving three. photons interacting with a nonlinear grating vector. Theoretical modeling is performed using wave vector additions and the results are compared to experimental measurements

Phases of inquiry-based learning: definitions and the inquiry cycle

International audienceInquiry-based learning is gaining popularity in science curricula, international research anddevelopment projects as well as teaching. One of the underlying reasons is that its successcan be significantly improved due to the recent technical developments that allow the inquiryprocess to be supported by electronic learning environments. Inquiry-based learning is oftenorganized into inquiry phases that together form an inquiry cycle. However, different variationson what is called the inquiry cycle can be found throughout the literature. The currentarticle focuses on identifying and summarizing the core features of inquiry-based learningby means of a systematic literature review and develops a synthesized inquiry cyclethat combines the strengths of existing inquiry-based learning frameworks. The review wasconducted using the EBSCO host Library; a total of 32 articles describing inquiry phasesor whole inquiry cycles were selected based on specific search criteria. An analysis of thearticles resulted in the identification of five distinct general inquiry phases: Orientation,Conceptualization, Investigation, Conclusion, and Discussion. Some of these phases are dividedinto sub-phases. In particular, the Conceptualization phase is divided into two (alternative)sub-phases, Questioning and Hypothesis Generation; the Investigation phase is dividedinto three sub-phases, Exploration or Experimentation leading to Data Interpretation; andthe Discussion phase is divided into two sub-phases, Reflection and Communication. Noframework bringing together all of these phases and sub-phases was found in the literature.Thus, a synthesized framework was developed to describe an inquiry cycle in whichall of these phases and sub-phases would be present. In this framework, inquiry-based learningbegins with Orientation and flows through Conceptualization to Investigation, whereseveral cycles are possible. Inquiry-based learning usually ends with the Conclusion phase.The Discussion phase (which includes Communication and Reflection) is potentially presentat every point during inquiry-based learning and connects to all the other phases, becauseit can occur at any time during (discussion in-action) or after inquiry-based learning whenlooking back (discussion on-action)