HRD-9628321 Bonner The production of smaller, more energy efficient lasers offer the promise of a convenient light source for many applications. The key to the efficiency is an understanding of the energy loss processes in the lasing media. Many useful lasers operate in quasi-four level mode where they experience large losses and low efficiencies. When the laser media is a crystal, the crystal field interacts with the energy manifolds of the dopant. The crystal field interaction can adjust the energy manifolds of the dopant in the crystal by as much as 500 cm-1 and cause large splittings relative to the free ion. The position and splittings of these manifolds are critical for efficient laser performance. The proposed research will investigate the effect of the crystal field on the critical factors affecting the performance of quasi-four level solid state cross sections which are key metrics in rare earth ion laser performance and the effects on processes such as energy transfer, upconversion, and non-radiative relaxation will provide full understanding of effect of the crystal field on laser performance. The degree crystal field splitting in the lower laser level and the upper level manifold dictates the thermal population on each level and ultimately laser performance. The larger crystal field splitting, the smaller the lower laser level population and higher upper laser level population. The decreased lower laser level and increased upper laser level populations and larger absorption and emission cross sections will significantly improve laser thresholds and slope efficiencies. A favorable effect of these splittings on key processes such as energy transfer, upconversion, inter-manifold, and intra- manifold relaxation contributes to improved laser performance. For the proposed three years, the specific objectives of the investigation are to determine the effect of crystal field on the threshold and slope efficiency of quasi-four level systems and understanding the field effects on the parameters and processes influencing laser performance. The effect of the crystal field on parameters such as absorption and emission cross sections, and processes such as energy transfer, upconversion and non-radiative relaxation will be studied. The fluorapatite family, specifically Ca5(PO4)3F, Sr5(PO4)3F, and Ba5(PO4)3F have been chosen since they are excellent candidates for efficient quasi-four level lasers due to their large crystal field splittings and crystal field parameters are varied by substitution of the alkaline earth metal. This trend on the crystal field parameters from Ca to Ba will be utilized to study its affect on the parameters and processes influencing the laser performance above mentioned. Tm3+ will be utilized as the probe since it exhibits a wealth of processes which affects the laser performance in many quasi-four level systems. Tm3+ itself is also an important quasi-four level laser ion. In the proposed investigation, a full understanding of the effect of crystal field parameters on quasi-four laser performance will be achieved while evaluating a potentially useful laser system such as Tm3+ doped fluoroapatites. The investigative team combines the expertise of crystal growth of high quality di-electric crystals, spectroscopy in solid state materials, ultrafast kinetics, and rare earth ion laser development. This team will grow, fabricate, and fully evaluate the materials in laboratories housed on campus. Temperature dependent absorption and emission will be used to determine the crystal field splitting, absorption and emission cross sections and energy branching ratios. Time resolved emission and absorption will be used to examine the radiative, non- radiative, and upconversion rates in the materials. A laser test bed will be constructed to evaluate the laser performance of the materials.

Agency
National Science Foundation (NSF)
Institute
Division of Human Resource Development (HRD)
Type
Standard Grant (Standard)
Application #
9628321
Program Officer
William A. Sibley
Project Start
Project End
Budget Start
1996-08-15
Budget End
1999-07-31
Support Year
Fiscal Year
1996
Total Cost
$261,063
Indirect Cost
Name
Norfolk State University
Department
Type
DUNS #
City
Norfolk
State
VA
Country
United States
Zip Code
23504