Sökning: "two-temperature model"

Visar resultat 1 - 5 av 8 avhandlingar innehållade orden two-temperature model.

1. 1. Ultrafast spin, lattice, and electron dynamics in thin metallic films : in the terahertz, near-infrared, and extreme ultraviolet regimes

   Författare :Vivek Unikandanunni; Stefano Bonetti; Andreas Rydh; Jurgen Lindner; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Terahertz; near-infrared; extreme ultraviolet; epitaxial cobalt; transient grating; field emission; gold; platinum; electron-phonon coupling; magneto-crystalline anisotropy; nanoscale dynamics; ultrafast spin dynamics; magnetic inertia; nutation; pump-probe; two-temperature model; Fowler-Nordheim tunneling; fysik; Physics;

   Sammanfattning : In this thesis, we studied the ultrafast spin and electron dynamics triggered by electromagnetic radiation belonging to three different regions of the electromagnetic spectrum, namely terahertz, near-infrared and extreme ultraviolet. By performing pump–probe measurements, we explored the role of the lattice in ultrafast spin and electron dynamics in metallic thin films. LÄS MER

3. 2. Ultrafast spin dynamics and relaxation in metallic ferromagnets

   Författare :Vivek Unikandanunni; Stefano Bonetti; Olof Karis; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Magnetization dynamics; Three temperature model; Cobalt; Anisotropy; Electron-phonon coupling; THz; Platinum; Silver; fysik; Physics;

   Sammanfattning : We performed ultrafast demagnetization measurements on epitaxial hcp-cobalt thin film with the easy axis in the plane of the film by pumping the sample with 400 nm radiation and probing the magneto-optic effects in the longitudinal magneto optic Kerr effect geometry using 800 nm radiation. The in-plane magnetic anisotropy of the sample enabled us to measure the demagnetization dynamics along two different crystalline directions, namely along the easy axis and at 45 degrees between the easy and hard axes. LÄS MER

4. 3. Studies of Material Properties using Ab Initio and Classical Molecular Dynamics

   Författare :Love Koči; Börje Johansson; Rajeev Ahuja; Dario Alfè; Uppsala universitet; []
   Nyckelord :Atomic and molecular physics; molecular dynamics; phase transitions; melting; elasticity; equation of state; metals; rare gases; Atom- och molekylfysik;

   Sammanfattning : In this thesis, material properties have been examined under extreme conditions in computer-based calculations.The research on iron (Fe), nickel (Ni), and ferropericlase (Mg1-xFexO) are not only important for our understanding of the Earth, but also for an improved knowledge of these materials per se. LÄS MER

5. 4. NbN and NbTiN Hot Electron Bolometer THz Mixers

   Författare :Pourya Khosropanah; Chalmers tekniska högskola; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; receiver noise; hot electron bolometer; superconducting detector; spiral antenna; NbTiN; submillimeter mixer; THz mixer; HEB; FTS; NbN; quasioptical receiver; heterodyne receiver; double slot antenna; twin slot antenna; Fourier Transform Spectrometer;

   Sammanfattning : The thesis reports the development of Hot Electron Bolometer (HEB) mixers for radio astronomy heterodyne receivers in THz frequency range. Part of this work is the fabrication of HEB devices, which are based on NbN or NbTiN superconducting thin films (≤5 nm). They are integrated with wideband spiral or double-slot planar antennas. LÄS MER

7. 5. Superconducting THz mixers based on MgB2 film

   Författare :Stella Bevilacqua; Chalmers tekniska högskola; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; bolometers; IF bandwidth.; superconductors; MgB2; THz Detectors; mixers;

   Sammanfattning : Superconducting NbN hot electron bolometer (HEB) mixers are widely used in terahertz radio astronomy. Such mixers have superior performance compared to SIS and Schottky diode mixers at frequency above 1THz. However, their drawback is a limited IF bandwidth. LÄS MER