CAP Simulation

A tool for simulating coherent acoustic phonon (CAP) interferometry experiments (also known as picosecond ultrasonics) in multilayered specimens. Originally developed by Justin Gregory at Vanderbilt University.

Usage

To simulate a given specimen, sub-class CapMaterialInterface and fill in the appropriate functions. See CapMaterialInterface.h and DefaultCapMaterial.h for instructions and an example.

Next, modify main.cpp to use your class instead of DefaultCapMaterial, and modify the transducing layer parameters as needed. See TransducingLayer.h for a description of each parameter, and the Thomsen et al. reference below for further detail.

Command Line Options

All have sensible defaults and are therefore optional.

-s <time_delay>, --start <time_delay>   Start time delay in seconds
-e <time_delay>, --stop <time_delay>    Stop time delay in seconds
-i <time_delay>, --step <time_delay>    Time delay step size in seconds
-R <value>,      --reflectivity <value> Force transducing layer reflectivity (useful for data fitting)
-q,              --quiet                Do not print parameters to stderr (will still be in stdout)
-t <number>,     --threads <number>     Number of simulation threads to run

Command Line Example

 $ ./cap-sim --start 0 --stop 150e-12 --step 0.25e-12 -t 8 > output.dat

Output

Simulation parameters are printed to stdout, with a '#' character at the beginning of each line. After that, there are two columns:

1. Time Delay (s)
2. Differential Reflectivity [(R - R0) / R0]

Where R0 is the base reflectivity of the specimen in the absence of the strain pulse.

Scientific References

• Picosecond ultrasonics

  http://en.wikipedia.org/wiki/Picosecond_ultrasonics

• Strain wave model

  C. Thomsen, H. Grahn, H. J. Maris and J. Tauc, "Surface Generation and Detection of Phonons by Picosecond Light Pulses", Phys. Rev. B. 34, 4129 (1986)).

• Modeling approach (characteristic matrices)

  O. Matsuda and O. B. Wright, "Reflection and transmission of light in multilayers perturbed by picosecond strain pulse propagation", J. Opt. Soc. Am. B 19, 3028-3041 (2002).

Potential Enhancements

• Calculation of reflectivity using Green's functions instead of characteristic matrices (see the Matsuda and Wright reference, above).
• Use the speed of sound information from the CapMaterialInterface subclass to calculate the acoustic impedence of the interfaces in the specimen, and model the resulting reflection and transmission of the acoustic pulse.