Issue 10 Volume 41 May 16, 2003

This report results from a contract tasking Koc University as follows: The contractor will investigate the use of
microcavities to control photoluminescence in amorphous silicon. This can lead to significant improvements in luminescent
displays, optical sensors, and optoelectronic devices. Amorphous siliconis of special interest since the material is abundant and
inexpensive.
DTIC
Amorphous Materials; Laser Cavities
20030033960 Lawrence Livermore National Lab., Livermore, CA
Final Report for High Precision Short-Pulse Laser Ablation System for Medical Applications
Kim, B. M.; Feit, M. D.; Rubenchik, A. M.; Marion, J. E.; Mar. 04, 2000; 14 pp.; In English
Report No.(s): DE2002-792650; No Copyright; Avail: Department of Energy Information Bridge
During the three year LDRD (Laboratory Directed Research and Development) funding period, we studied the ablation
characteristics of biological tissues using ultrashort pulse lasers (USPL) with pulse widths varying from 100 femtoseconds to
tens of picoseconds. During the first year, we performed extensive theoretical studies to develop an improved understanding
of the USPL (ultra short pulsed laser) ablation process. Two optical signals were tested for feasibility of use in real-time
feedback systems during high repetition rate ablation. In the second year, we devised a real-time, feedback-controlled USPL
ablation system, based on luminescence, which may be useful for sensitive micro-spinal surgeries. Effective laser parameters
were identified to reduce collateral damage. The final year of the project focused on quantification of the pressure pulse
induced by USPL ablation of water surfaces representing biological tissues. Results of these studies were presented in invited
talks at domestic and international conferences and numerous journal articles were published.
NTIS
Medical Equipment; Laser Ablation; Ultrashort Pulsed Lasers; Tissues (Biology)
20030034631 Air Force Research Lab., Edwards AFB, CA
The Accuracy of Remapping Irregularly Spaced Velocity Data onto a Regular Grid and the Computation of Vorticity
Cohn, Richard K.; Koochesfahani, Manoochehr M.; November 30, 1999; 9 pp.; In English
Contract(s)/Grant(s): AF Proj. 3058
Report No.(s): AD-A410269; AFRL-PR-ED-TP-1999-0218; No Copyright; Avail: CASI; A02, Hardcopy
The velocity data obtained from Molecular Tagging Velocimetry (MTV) are typically located on an irregularly spaced
measurement grid. To take advantage of many standard data processing techniques, the MTV data need to be remapped onto
a grid with a uniform spacing. In this work, accuracy and noise issues related to the use of a least-squares-fit to various
low-order polynomials for the remapping of these data onto a uniformly spaced grid and the subsequent computation of
vorticity from these data are examined. This information has relevance to PIV data processing as well. As noted by Spedding
and Rignot (1993), the best estimate of the velocity vector acquired through the use of tracer techniques such as PIV is at the
midpoint of the displacement vector. Thus, unless special care is taken, PlV data also are initially obtained on an irregular grid.
As in the results of Fouras and Soria (l998), the error in the remapped velocity and the calculated vorticity field is divided into
a mean bias error and a random error. In the majority of cases, the mean bias error is a more significant source of error than
the more often quoted random error. Results of the simulation show that the best choice for remapping is the use of a
least-squares fit to a 2nd order polynomial and the best choice for vorticity calculation is to use a 4th order accurate, central,
finite difference applied to uniformly sampled data. The actual value of the error depends upon the data density and the radius
used for the selection of velocity measurements to be included in the remapping process. Increasing the data density and
reducing the fit radius improve the accuracy.
DTIC
Particle Image Velocimetry; Velocity Measurement; Vorticity; Mathematical Models; Accuracy; Fluid Mechanics;
Computational Grids
20030034635 Air Force Research Lab., Edwards AFB, CA
Vorticity Field Evolution in a Forced Wake
Cohn, Richard; Koochesfahani, Manoochehr; March 15, 1999; 5 pp.; In English
Contract(s)/Grant(s): AF Proj. 3058
Report No.(s): AD-A410275; AFRL-PR-ED-TP-FY99-0059; No Copyright; Avail: CASI; A01, Hardcopy
The purpose of this work is to quantify the vorticity evolution in the flow field of the forced wake of a splitter plate inside
a confining geometry. The interest in this flow stems from the fact that forcing a low Reynolds number 2-D wake can lead
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