First Experimental Proof of Raizer–Zeldovich Theorem (or RZ-Theory). SID SENADHEERA Mechanical Engineering Department Ryerson University. Different methods of producing nanofibers. Experimental Setup. Computer simulation of heat dissipation in laser ablation.
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First Experimental Proof of
SID SENADHEERAMechanical Engineering DepartmentRyerson University
Different methods of producing nanofibers
Computersimulation of heat dissipation in laser ablation
* Initially, the vapor expansion proceeds along the Poisson adiabat with : PVγ= const.
P-V diagram with the Causius-Clapeyron equation
According to RZ-theory the following equation can be written
Condensation rate : dx/dt
Nucleation rate : dν/dt
Atomic clustering rate : dg/dt
x(t) = ν(t).g(t)
Nucleation rate can be expanded as :
*The sharp increment in nucleation occurs at phase transformation
*The time component for Graphite and Silicon can be theoretically graphed as below to estimate the times for phase transformations.
The first theoretical analysis of condensation dynamics in a rapidly expanding vapor was performed by
Raizer et al. in 1958. Anisimov et al. did the next detailed study on the theory with the results below.
(a) Temperature Variations
(d) Nucleation rate is ν(t)
(b) Supercooling Parameter
(e) Cluster dimension variation
(c) Vapor condensationx(t)
(f) Atomic clustering g(t)
EXPERIMENTAL PROOF OF R-Z THEORY
INTRODUCTION TO FEMTOSECOND LASER PULSES
* Crystallization and formation of fibers start at a lower pulse
frequency for Graphite crystals (less than 1 MHz) and for Silicon (~2MHz)
Starts nucleation at 2 MHz
Starts nucleation at 1 MHz
Interpulse time unit ~ 0.5 μs
Interpulse time unit ~ 1 μs
(below graph) are in close agreement with the experimental values (above).
R(t) ~ (Eo/ro)1/5 t2/5
Video clip – Please click on picture below
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Yakov B. Zeldovich (left), Andrei Sakharov (middle),
and David A. Frank-Kamenetskii in Sarov, 1950s
-Russian Academy of Sciences