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Physics-Ellipsometry-VASE-0.03
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Physics::Ellipsometry::VASE

Variable Angle Spectroscopic Ellipsometry data fitting for Perl / PDL.

Description

Physics::Ellipsometry::VASE provides a framework for fitting optical thin-film models to VASE data using the Levenberg-Marquardt algorithm. It handles:

Installation

From CPAN:

cpanm Physics::Ellipsometry::VASE

From source:

perl Makefile.PL
make
make test
make install

Synopsis

use PDL;
use PDL::NiceSlice;
use Physics::Ellipsometry::VASE;

my $vase = Physics::Ellipsometry::VASE->new(layers => 1);
$vase->load_data('measurement.dat');

sub my_model {
    my ($params, $x) = @_;
    my $wavelength = $x->(:,0);   # nm
    my $angle      = $x->(:,1);   # degrees

    my $psi   = $params->(0) + $params->(1) / $wavelength**2;
    my $delta = $params->(2) + $params->(3) * $wavelength;

    return cat($psi, $delta)->flat;
}

$vase->set_model(\&my_model);
my $fitted = $vase->fit(pdl [45, 1e4, 120, 0.01]);

# Optional: plot results (requires PDL::Graphics::Gnuplot)
$vase->plot($fitted, output => 'fit.png');

Data Formats

Simple format

# Wavelength(nm)  Angle(deg)  Psi(deg)  Delta(deg)
400  70  45.0  120.0
410  70  44.5  121.0

Woollam VASE format

Recognised automatically when line 2 begins with VASEmethod[. Header metadata is stored as object attributes; sigma columns are extracted and used as fit weights.

Example Woollam file format:

w1_11012006
VASEmethod[EllipsometerType=4, Isotropic, FixedPol=45.00, ZoneAve=1, Revs=40, OffsetMode=2, Offset1=0, Offset2=0, Offset3=0, WVASE=3.616, HardVer=17.034, Wed Nov 01 15:19:00 2006]
Original[w1_11012006.dat]
nm
245.732520	64.999634	14.355849	149.18707	0.04032	0.132363
247.331348	64.999634	14.181567	150.33243	0.0433035	0.141132

Loading Woollam files:

use Physics::Ellipsometry::VASE;
use PDL;

my $vase = Physics::Ellipsometry::VASE->new(layers => 1);
my $data = $vase->load_data('woollam_data.dat');

# Access header metadata
print "Sample: ", $vase->{sample_name}, "\n";        # w1_11012006
print "Method: ", $vase->{vase_method}, "\n";        # VASEmethod[...] content
print "Original: ", $vase->{original_file}, "\n";    # Original[...] content
print "Units: ", $vase->{units}, "\n";               # nm

# Access measurement uncertainties (automatically used as fit weights)
if (defined $vase->{sigma}) {
    my $sigma_psi   = $vase->{sigma}->(0,:);  # psi uncertainties
    my $sigma_delta = $vase->{sigma}->(1,:);  # delta uncertainties
    print "Has sigma columns for weighted fitting\n";
}

The weighted fitting automatically uses the sigma columns when present, giving less weight to measurements with larger uncertainties during the Levenberg-Marquardt optimization.

Examples

The examples/ directory contains working scripts:

| Script | Description | |--------|-------------| | fit_linear.pl | Minimal linear dispersion model | | vase_test_fit.pl | Cauchy thin-film model (Ta₂O₅ on Si) with complex Fresnel equations | | vase_tauc_lorentz_fit.pl | Tauc-Lorentz oscillator with numerical Kramers-Kronig |

Model Function Contract

sub model {
    my ($params, $x) = @_;
    # $params — PDL piddle of fit parameters
    # $x      — (npts, 2) piddle: col 0 = wavelength (nm), col 1 = angle (deg)
    #
    # Must return: cat($psi, $delta)->flat
    #   — flat piddle of length 2*npts (all psi then all delta)
}

Dependencies

Author

Jovan Trujillo jtrujil1@asu.edu

License

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.