:orphan:

.. ****************************************************************************
.. CUI
..
.. The Advanced Framework for Simulation, Integration, and Modeling (AFSIM)
..
.. The use, dissemination or disclosure of data in this file is subject to
.. limitation or restriction. See accompanying README and LICENSE for details.
.. ****************************************************************************

Fluence_model
-------------

.. command:: fluence_model ... end_fluence_model
    :block:

    .. parsed-literal::

     fluence_model_  :ref:`<fluence-model-type-name> <Fluence_Model.Fluence_Model_Types>`
       aperture_diameter_ ...
       atmospheric_structure_ ...
       beam_quality_ ...
       calculate_incidence_ ...
       jitter_ ...
       laser_type_ ...
       power_ ...
       wavelength_ ...
       ... :ref:`derived model type commands <Fluence_Model.Fluence_Model_Types>`
     end_fluence_model

Overview
========

The fluence model is utilized by :model:`WSF_LASER_WEAPON` and :model:`WSF_CUED_LASER_WEAPON` to calculate beam spread and beam
loss due to jitter, diffraction, atmospheric turbulence, extinction, and target effects.

.. note::
      The default method of calculating target geometry is to assume a head-on, maximally effective aspect. 
      This may be modified with a cosine rolloff with the use of the calculate_incidence_ input. 
      However, the best way to model the target geometry is with a :model:`WSF_INTERSECT_PROCESSOR` and the use of intersection
      meshes that represent the target geometry within the simulation.

.. _Fluence_Model.Fluence_Model_Types:

**<fluence-model-type-name>** Specifies one of the :ref:`Fluence Model Types <Fluence_Model.Fluence_Model_Types>`:

.. include:: fluence_model_types.txt

.. _fluence_model.commands:

Commands
========

.. command:: aperture_diameter <length-value> 
   
   The aperture diameter of the HEL system.  Changing this parameter controls the diffraction-induced beam spread,
   affecting the beam size on target.  The larger the aperture diameter, the smaller the beam on target, and the greater
   the energy density (energy density ~ (aperture diameter^2)).

.. _fluence_model.atmospheric_structure:
.. include:: turbulence_commands.txt

.. command:: beam_quality <real-value> 
   
   Specify the beam quality of the optical system.  The beam quality is a measure of how close the profile is to a perfect
   gaussian.  Specifically it is a multiplicative factor times the diffraction-limited radius.  It varies from a value of
   1 (diffraction limited) to values of order unity (but still greater than one).
   
   **Default** 1.1

.. command:: calculate_incidence <boolean-value> 
   
   Specify whether to calculate an incidence angle on target based on aspect, with a head-on aspect to target representing
   the minimum (0 degree) incidence.  Any incidence greater than 90 degrees would be considered ineffective.

   **Default** *disabled*

   .. note::
      This feature has been superseded by use of intersection meshes and the :model:`WSF_INTERSECT_PROCESSOR`.

.. command:: jitter <angle-value> 
   
   Specify the jitter of the system (typically on the order of microradians).  The higher the jitter, the more a HEL beam
   will be "spread out" over the target.
   
   **Default** 6.6e-7

.. command:: laser_type  carbon_dioxide | nd_yag | coil | deuterium_fluoride 
   
   Specify the high-energy laser type.  In turn this specifies the wavelength, which is needed by the various models to
   calculate diffraction and extinction of the beam.

   .. note::
      Currently use of this command is preferred over wavelength_.

   .. note::
      This value, along with :command:`fluence_model.default.haze_model` and
      :command:`fluence_model.default.atmosphere_model` is used to load a table of :command:`atmospheric_coefficients` generated by
      ModTran.

.. command:: power <power-value> 
   
   This is the actual laser power emitted from the aperture.

.. command:: wavelength <length-value> 
   
   The wavelength at which the laser operates (e.g., 1.064 microns for a Nd-YAG laser).  Current supported wavelengths (in
   nanometers) include

   * 1000 (Carbon Dioxide)
   * 1064 (Nd:YAG)
   * 1315 (COIL- Iodine Lasing)
   * 3800 (Deuterium Fluoride)

   .. note::
      This value, along with :command:`fluence_model.default.haze_model` and
      :command:`fluence_model.default.atmosphere_model` is used to load a table of :command:`atmospheric_coefficients` generated by
      ModTran.

   .. note::
      See the "hel_demo" example directory in the standard release for the necessary files corresponding
      with these atmosphere models.