added helper attributes

lib/Physics/UEMColumn/Pulse.pm

@@ -103,15 +103,13 @@ has 'liouville_gamma2_z' => ( isa => 'Num', is => 'rw', lazy => 1, builder => '_
 
 # variance attribute initializers
 method _make_sigma_t () {
-  return (($self->width)**2) / 2;
+  return $self->initial_width ** 2 / 2;
 }
 method _make_sigma_z () {
-  return (($self->velocity * $self->duration)**2) / 2;
-}
+  return $self->initial_length ** 2 / 2;
 
 method _make_eta_t () {
-  #me * $energy_fermi / 3 * ( $energy_laser - $work_function ) / ( $energy_laser + $energy_fermi );
-  return 0;
+  return me * $self->excess_photoemission_energy / 3;
 }
 method _make_eta_z () {
   return $self->eta_t() / 4;
@@ -131,6 +129,26 @@ method _make_lg2_z () {
   return $self->sigma_z * $self->eta_z;
 }
 
+# initialization-only attributes
+
+=item C<initial_width> / C<initial_length>
+
+These attributes are for convenience only. They may be used to initialize the variance attriutes above. They represent the initial half-width 1/e maximum (HW1/eM) width or length of the pulse. Unit: m
+
+=cut
+
+my $unit_length = num_of_unit('m');
+has 'initial_width'  => ( isa => $unit_length, is => 'ro', default => '1 mm' );
+has 'initial_length' => ( isa => $unit_length, is => 'ro', default => '1 mm' );
+
+=item C<initial_width> / C<initial_length>
+
+This attribute is for convenience only. It may be used to initialize the variance attriutes above. It represents the excess photoemission energy imparted to the electrons in the pulse by simple photoemission. Unit: J
+
+=cut
+
+has 'excess_photoemission_energy' => ( isa => num_of_unit('J'), is => 'ro', default => '0.5 eV' );
+
 # propagation history
 
 =item C<data>