Role of local modes in nonradiative processes taking place in impurity-doped laser crystals.
Item
-
Title
-
Role of local modes in nonradiative processes taking place in impurity-doped laser crystals.
-
Identifier
-
AAI9807910
-
identifier
-
9807910
-
Creator
-
Calistru, Dana Manuela.
-
Contributor
-
Adviser: Robert R. Alfano
-
Date
-
1997
-
Language
-
English
-
Publisher
-
City University of New York.
-
Subject
-
Physics, Condensed Matter | Physics, Optics
-
Abstract
-
This thesis presents the identification and characterization in terms of energy and symmetry of Cr{dollar}\sp{lcub}4+{rcub}{dollar} local modes in the Cr:Mg{dollar}\rm\sb2SiO\sb4{dollar} tunable solid state laser, as well as their role and dynamics during nonradiative processes, using steady state and time resolved resonance Raman measurements.;The main feature which makes Cr:Mg{dollar}\rm\sb2SiO\sb4{dollar} suitable for studying the role of a laser ion's (Cr{dollar}\sp{lcub}4+{rcub}){dollar} local modes during nonradiative relaxation is that the room temperature quantum efficiency for this laser crystal is {dollar}\sim{dollar}10% due to strong nonradiative processes. The local modes of Cr{dollar}\sp{lcub}4+{rcub}{dollar} were identified in terms of energy and symmetry using polarized steady state resonance Raman scattering. Seven (out of the expected nine) Cr{dollar}\sp{lcub}4+{rcub}{dollar} local modes were identified in room temperature resonance Raman spectra having the following energy and symmetry (the symmetry for each mode is given in both the site C{dollar}\rm\sb{lcub}s{rcub}{dollar} and the undistorted T{dollar}\rm\sb{lcub}d{rcub}{dollar} (in parenthesis) symmetries): 765 cm{dollar}\sp{lcub}-1{rcub}{dollar} - {dollar}\rm A\sp\prime(A\sb1),\ 740\ cm\sp{lcub}-1{rcub}{dollar} - {dollar}\rm A\sp{lcub}\prime\prime{rcub}(T\sb2),\ 690\ cm\sp{lcub}-1{rcub}{dollar} - {dollar}\rm A\sp\prime(T\sb2),\ 498\ cm\sp{lcub}-1{rcub}{dollar} - {dollar}\rm A\sp\prime(E),\ 480\ cm\sp{lcub}-1{rcub}{dollar} - {dollar}\rm A\sp{lcub}\prime\prime{rcub}(E),\ 290\ cm\sp{lcub}-1{rcub}{dollar} - {dollar}\rm A\sp\prime(T\sb2),\ 253\ cm\sp{lcub}-1{rcub}{dollar} - {dollar}\rm A\sp\prime(T\sb2).{dollar} Force constant calculations show a decrease of 13-19% in the intra-tetrahedral force constants for a CrO{dollar}\sb4{dollar} molecule if compared to a SiO{dollar}\sb4{dollar} molecule.;Low temperature resonance Raman spectra which offer improved resonance conditions reveal an anomalous number of 15 local modes, i.e. an increased number of decay channels for nonradiative processes, which was attributed to second neighbor interactions. This is the first report of second neighbor interactions observed using resonance Raman scattering.;Time resolved resonance Raman measurements performed with 500 fs pulses probed the dynamics of Cr{dollar}\sp{lcub}4+{rcub}{dollar} local modes following the {dollar}\rm\sp3B\sb2(\sp3T\sb1){dollar} - {dollar}\sp1{dollar}E bottleneck crossing. It was shown that during the nonradiative relaxation the energy from the nonequilibrium local mode population created following the bottleneck transition is transferred into a select number of daughter phonon modes. The daughter phonons decay due to anharmonic interactions with the phonon bath and the system returns to thermal equilibrium. The following parameters characterizing the nonradiative decay were estimated from time-resolved measurements: bottleneck transition time {dollar}\sim{dollar}2.8 ps, local mode lifetime {dollar}\sim{dollar}5.1 ps, phonon mode lifetime {dollar}\sim{dollar}5 ps. This is the first report on the dynamics of a laser ion's local modes during the nonradiative relaxation in an impurity-doped laser crystal.
-
Type
-
dissertation
-
Source
-
PQT Legacy CUNY.xlsx
-
degree
-
Ph.D.
