NXopt.nxdl.xml

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="nxdlformat.xsl"?>
<!--
# NeXus - Neutron and X-ray Common Data Format
# 
# Copyright (C) 2014-2024 NeXus International Advisory Committee (NIAC)
# 
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 3 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#
# For further information, see http://www.nexusformat.org
-->
<!--05/2023
Draft of a NeXus application definition which serves as a template for various
optical spectroscopy experiments-->
<!--To do:
[ ] Check base classes (NXbeam_path + base classes used by it)
[ ] Harmonize NXopt and NXellipsometry
[ ] Fix dimensions and ranks-->
<definition xmlns="http://definition.nexusformat.org/nxdl/3.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" category="application" name="NXopt" extends="NXobject" type="group" xsi:schemaLocation="http://definition.nexusformat.org/nxdl/3.1 ../nxdl.xsd">
    <symbols>
        <doc>
             Variables used throughout the document, e.g. dimensions or parameters.
        </doc>
        <symbol name="N_spectrum">
            <doc>
                 Length of the spectrum array (e.g. wavelength or energy) of the measured
                 data.
            </doc>
        </symbol>
        <symbol name="N_sensors">
            <doc>
                 Number of sensors used to measure parameters that influence the sample,
                 such as temperature or pressure.
            </doc>
        </symbol>
        <symbol name="N_measurements">
            <doc>
                 Number of measurements (1st dimension of measured_data array). This is
                 equal to the number of parameters scanned. For example, if the experiment
                 was performed at three different temperatures and two different pressures
                 N_measurements = 2*3 = 6.
            </doc>
        </symbol>
        <symbol name="N_detection_angles">
            <doc>
                 Number of detection angles of the beam reflected or scattered off the
                 sample.
            </doc>
        </symbol>
        <symbol name="N_incident_angles">
            <doc>
                 Number of angles of incidence of the incident beam.
            </doc>
        </symbol>
        <symbol name="N_observables">
            <doc>
                 Number of observables that are saved in a measurement. e.g. one for
                 intensity, reflectivity or transmittance, two for Psi and Delta etc. This
                 is equal to the second dimension of the data array 'measured_data' and the
                 number of column names.
            </doc>
        </symbol>
    </symbols>
    <doc>
         An application definition for optical spectroscopy experiments.
    </doc>
    <group type="NXentry">
        <doc>
             An application definition template for optical spectroscopy experiments.
             
             A general optical experiment consists of a light or excitation source, a
             beam path, a sample + its stage + its environment, and a detection unit.
             Examples are reflection or transmission measurements, photoluminescence,
             Raman spectroscopy, ellipsometry etc.
        </doc>
        <field name="definition">
            <doc>
                 An application definition describing a general optical experiment.
            </doc>
            <attribute name="version">
                <doc>
                     Version number to identify which definition of this application
                     definition was used for this entry/data.
                </doc>
            </attribute>
            <attribute name="url">
                <doc>
                     URL where to find further material (documentation, examples) relevant
                     to the application definition.
                </doc>
            </attribute>
            <enumeration>
                <item value="NXopt"/>
            </enumeration>
        </field>
        <field name="experiment_identifier">
            <doc>
                 A (globally persistent) unique identifier of the experiment.
                 (i) The identifier is usually defined by the facility or principle
                 investigator.
                 (ii) The identifier enables to link experiments to e.g. proposals.
            </doc>
        </field>
        <field name="experiment_description" optional="true">
            <doc>
                 An optional free-text description of the experiment.
                 
                 However, details of the experiment should be defined in the specific
                 fields of this application definition rather than in this experiment
                 description.
            </doc>
        </field>
        <field name="experiment_type">
            <doc>
                 Specify the type of the optical experiment.
            </doc>
        </field>
        <field name="start_time" type="NX_DATE_TIME">
            <doc>
                 Start time of the experiment. UTC offset should be specified.
            </doc>
        </field>
        <group type="NXuser">
            <doc>
                 Contact information of at least the user of the instrument or the
                 investigator who performed this experiment.
                 Adding multiple users, if relevant, is recommended.
            </doc>
            <field name="name" type="NX_CHAR">
                <doc>
                     Name of the user.
                </doc>
            </field>
            <field name="affiliation" type="NX_CHAR" recommended="true">
                <doc>
                     Name of the affiliation of the user at the point in time when the
                     experiment was performed.
                </doc>
            </field>
            <field name="address" type="NX_CHAR" recommended="true">
                <doc>
                     Street address of the user's affiliation.
                </doc>
            </field>
            <field name="email" type="NX_CHAR">
                <doc>
                     Email address of the user.
                </doc>
            </field>
            <field name="orcid" type="NX_CHAR" recommended="true">
                <doc>
                     Author ID defined by https://orcid.org/.
                </doc>
            </field>
            <field name="telephone_number" type="NX_CHAR" recommended="true">
                <doc>
                     Telephone number of the user.
                </doc>
            </field>
        </group>
        <group type="NXinstrument">
            <doc>
                 Properties of the experimental setup. This includes general information
                 about the instrument (such as model, company etc.), information about
                 the calibration of the instrument, elements of the beam path including
                 the excitation or light source and the detector unit, the sample stage
                 (plus the sample environment, which also includes sensors used to
                 monitor external conditions) and elements of the beam path.
                 
                 Meta data describing the sample should be specified in ENTRY/SAMPLE
                 outside of ENTRY/INSTRUMENT.
            </doc>
            <field name="model">
                <doc>
                     The name of the instrument.
                </doc>
                <attribute name="version">
                    <doc>
                         The used version of the hardware if available. If not a commercial
                         instrument use date of completion of the hardware.
                    </doc>
                </attribute>
            </field>
            <field name="company" optional="true">
                <doc>
                     Name of the company which build the instrument.
                </doc>
            </field>
            <field name="construction_year" type="NX_DATE_TIME" optional="true">
                <doc>
                     ISO8601 date when the instrument was constructed.
                     UTC offset should be specified.
                </doc>
            </field>
            <group name="software" type="NXprocess">
                <field name="program">
                    <doc>
                         Commercial or otherwise defined given name of the program that was
                         used to measure the data, i.e. the software used to start and
                         record the measured data and/or metadata.
                         If home written, one can provide the actual steps in the NOTE
                         subfield here.
                    </doc>
                </field>
                <field name="version">
                    <doc>
                         Either version with build number, commit hash, or description of a
                         (online) repository where the source code of the program and build
                         instructions can be found so that the program can be configured in
                         such a way that result files can be created ideally in a
                         deterministic manner.
                    </doc>
                </field>
                <attribute name="url" optional="true">
                    <doc>
                         Website of the software.
                    </doc>
                </attribute>
            </group>
            <group name="firmware" type="NXprogram" recommended="true">
                <doc>
                     Commercial or otherwise defined name of the firmware that was used
                     for the measurement - if available.
                </doc>
                <attribute name="version">
                    <doc>
                         Version and build number or commit hash of the software source code.
                    </doc>
                </attribute>
                <attribute name="url" optional="true">
                    <doc>
                         Website of the software.
                    </doc>
                </attribute>
            </group>
            <field name="calibration_status" type="NX_CHAR">
                <doc>
                     Was a calibration performed? If yes, when was it done? If the
                     calibration time is provided, it should be specified in
                     ENTRY/INSTRUMENT/calibration/calibration_time.
                </doc>
                <enumeration>
                    <item value="calibration time provided"/>
                    <item value="no calibration"/>
                    <item value="within 1 hour"/>
                    <item value="within 1 day"/>
                    <item value="within 1 week"/>
                </enumeration>
            </field>
            <group name="calibration" type="NXsubentry" recommended="true">
                <doc>
                     The calibration data and metadata should be described in a separate NeXus file
                     with the link provided in 'calibration_link'.
                </doc>
                <field name="calibration_time" type="NX_DATE_TIME" optional="true">
                    <doc>
                         If calibtration status is 'calibration time provided', specify the
                         ISO8601 date when calibration was last performed before this
                         measurement. UTC offset should be specified.
                    </doc>
                </field>
                <field name="calibration_data_link">
                    <doc>
                         Link to the NeXus file containing the calibration data and metadata.
                    </doc>
                </field>
            </group>
            <group type="NXbeam_path">
                <doc>
                     Describes an arrangement of optical or other elements, e.g. the beam
                     path between the light source and the sample, or between the sample
                     and the detector unit (including the sources and detectors
                     themselves).
                     
                     If a beam splitter (i.e. a device that splits the incoming beam into
                     two or more beams) is part of the beam path, two or more NXbeam_path
                     fields may be needed to fully describe the beam paths and the correct
                     sequence of the beam path elements.
                     Use as many beam paths as needed to describe the setup.
                </doc>
            </group>
            <field name="angle_of_incidence" type="NX_NUMBER" units="NX_ANGLE">
                <doc>
                     Angle(s) of the incident beam vs. the normal of the bottom reflective
                     (substrate) surface in the sample.
                </doc>
                <dimensions rank="1">
                    <dim index="1" value="N_incident_angles"/>
                </dimensions>
                <attribute name="units"/>
            </field>
            <field name="detection_angle" type="NX_NUMBER" optional="true" units="NX_ANGLE">
                <doc>
                     Detection angle(s) of the beam reflected or scattered off the sample
                     vs. the normal of the bottom reflective (substrate) surface in the
                     sample if not equal to the angle(s) of incidence.
                </doc>
                <dimensions rank="1">
                    <dim index="1" value="N_detection_angles"/>
                </dimensions>
            </field>
            <group name="sample_stage" type="NXsubentry">
                <doc>
                     Sample stage, holding the sample at a specific position in X,Y,Z
                     (Cartesian) coordinate system and at an orientation defined
                     by three Euler angles (alpha, beta, gamma).
                </doc>
                <field name="stage_type">
                    <doc>
                         Specify the type of the sample stage.
                    </doc>
                    <enumeration>
                        <item value="manual stage"/>
                        <item value="scanning stage"/>
                        <item value="liquid stage"/>
                        <item value="gas cell"/>
                        <item value="cryostat"/>
                    </enumeration>
                </field>
                <field name="alternative" optional="true">
                    <doc>
                         If there is no motorized stage, we should at least qualify where
                         the beam hits the sample and in what direction the sample stands
                         in a free-text description, e.g. 'center of sample, long edge
                         parallel to the plane of incidence'.
                    </doc>
                </field>
                <group name="environment_conditions" type="NXenvironment">
                    <doc>
                         Specify external parameters that have influenced the sample, such
                         as the surrounding medium, and varied parameters e.g. temperature,
                         pressure, pH value, optical excitation etc.
                    </doc>
                    <field name="medium">
                        <doc>
                             Describe what was the medium above or around the sample. The
                             common model is built up from the substrate to the medium on the
                             other side. Both boundaries are assumed infinite in the model.
                             Here, define the name of the medium (e.g. water, air, UHV, etc.).
                        </doc>
                    </field>
                    <field name="medium_refractive_indices" type="NX_FLOAT" optional="true" units="NX_UNITLESS">
                        <doc>
                             Array of pairs of complex refractive indices n + ik of the medium
                             for every measured spectral point/wavelength/energy.
                             Only necessary if the measurement was performed not in air, or
                             something very well known, e.g. high purity water.
                        </doc>
                        <dimensions rank="2">
                            <dim index="1" value="2"/>
                            <dim index="2" value="N_spectrum"/>
                        </dimensions>
                    </field>
                    <group name="PARAMETER" type="NXsensor" optional="true">
                        <doc>
                             A sensor used to monitor an external condition influencing the
                             sample, such as temperature or pressure. It is suggested to
                             replace 'PARAMETER' by the type of the varied parameter defined
                             in 'parameter_type'.
                             The measured parameter values should be provided in 'values'.
                             For each parameter, a 'PARAMETER(NXsensor)' field needs to exist.
                             In other words, there are N_sensors 'PARAMETER(NXsensor)' fields.
                        </doc>
                        <field name="parameter_type">
                            <doc>
                                 Indicates which parameter was changed. Its definition must exist
                                 below. The specified variable has to be N_measurements long,
                                 providing the parameters for each data set. If you vary more than
                                 one parameter simultaneously.
                                 If the measured parameter is not contained in the list `other`
                                 should be specified and the `parameter_type_name` should be provided.
                            </doc>
                            <enumeration>
                                <item value="conductivity"/>
                                <item value="detection_angle"/>
                                <item value="electric_field"/>
                                <item value="flow"/>
                                <item value="incident_angle"/>
                                <item value="magnetic_field"/>
                                <item value="optical_excitation"/>
                                <item value="pH"/>
                                <item value="pressure"/>
                                <item value="resistance"/>
                                <item value="shear"/>
                                <item value="stage_positions"/>
                                <item value="strain"/>
                                <item value="stress"/>
                                <item value="surface_pressure"/>
                                <item value="temperature"/>
                                <item value="voltage"/>
                                <item value="other"/>
                            </enumeration>
                        </field>
                        <field name="parameter_type_name" optional="true">
                            <doc>
                                 If the parameter_type is `other` a name should be specified here.
                            </doc>
                        </field>
                        <field name="number_of_parameters" type="NX_POSINT" units="NX_UNITLESS">
                            <doc>
                                 Number of different parameter values at which the measurement
                                 was performed. For example, if the measurement was performed at
                                 temperatures of 4, 77 and 300 K, then number_of_parameters = 3.
                            </doc>
                        </field>
                        <field name="values" type="NX_FLOAT" units="NX_ANY">
                            <doc>
                                 Vector containing the values of the varied parameter. Its
                                 length is equal to N_measurements. The order of the values
                                 should be as follows:
                                 
                                 * Order the sensors according to number_of_parameters starting
                                   with the lowest number. If number_of_parameters is equal for
                                   two sensors order them alphabetically (sensor/parameter name).
                                 * The first sensor's j parameters should be ordered in the
                                   following way. The first N_measurements/number_of_parameters
                                   entries of the vector contain the first parameter (a1), the
                                   second N_measurements/number_of_parameters contain the second
                                   parameter (a2) etc., so the vector looks like:
                                   [
                                   a1,a1,...,a1,
                                   a2,a2,...,a2,
                                   ...
                                   aj,aj,...aj
                                   ]
                                 * The kth sensor's m parameters should be ordered in the
                                   following way:
                                   [
                                   p1,...p1,p2,...,p2,...pm,...,pm,
                                   p1,...p1,p2,...,p2,...pm,...,pm,
                                   ...
                                   p1,...p1,p2,...,p2,...pm,...,pm
                                   ]
                                 * The last sensor's n parameters should be ordered in the
                                   following way:
                                   [
                                   z1,z2,...,zn,
                                   z1,z2,...,zn,
                                   ...
                                   z1,z2,...,zn]
                                 
                                 For example, if the experiment was performed at three different
                                 temperatures (T1, T2, T3), two different pressures (p1, p2) and
                                 two different angles of incidence (a1, a2), then
                                 N_measurements = 12 and the order of the values for the various
                                 parameter vectors is:
                                 
                                 * angle_of_incidence: [a1,a1,a1,a1,a1,a1,a2,a2,a2,a2,a2,a2]
                                 * pressure: [p1,p1,p1,p2,p2,p2,p1,p1,p1,p2,p2,p2]
                                 * temperature: [T1,T2,T3,T1,T2,T3,T1,T2,T3,T1,T2,T3]
                            </doc>
                            <dimensions rank="1">
                                <dim index="1" value="N_measurements"/>
                            </dimensions>
                        </field>
                    </group>
                </group>
                <group name="WINDOW" type="NXaperture" optional="true">
                    <doc>
                         For environmental measurements, the environment (liquid, vapor
                         etc.) is enclosed in a cell, which has windows both in the
                         direction of the source (entry window) and the detector (exit
                         window) (looking from the sample). In case that the entry and exit
                         windows are not the same type and do not have the same properties,
                         use a second 'WINDOW(MXaperture)' field.
                         
                         The windows also add a phase shift to the light altering the
                         measured signal. This shift has to be corrected based on measuring
                         a known sample (reference sample) or the actual sample of interest
                         in the environmental cell. State if a window correction has been
                         performed in 'window_effects_corrected'. Reference data should be
                         considered as a separate experiment, and a link to the NeXus file
                         should be added in reference_data_link in measured_data.
                         
                         The window is considered to be a part of the sample stage but also
                         beam path. Hence, its position within the beam path should be
                         defined by the 'depends_on' field.
                    </doc>
                    <field name="depends_on" recommended="true">
                        <doc>
                             Specify the position of the window in the beam path by pointing
                             to the preceding element in the sequence of beam path elements.
                        </doc>
                    </field>
                    <field name="window_effects_corrected" type="NX_BOOLEAN">
                        <doc>
                             Was a window correction performed? If 'True' describe the window
                             correction procedure in 'window_correction/procedure'.
                        </doc>
                    </field>
                    <group name="window_correction" type="NXprocess" optional="true">
                        <doc>
                             Was a window correction performed? If 'True' describe the
                             window correction procedure in ''
                        </doc>
                        <field name="procedure">
                            <doc>
                                 Describe when (before or after the main measurement + time
                                 stamp in 'date') and how the window effects have been
                                 corrected, i.e. either mathematically or by performing a
                                 reference measurement. In the latter case, provide the link to
                                 to the reference data in 'reference_data_link'.
                            </doc>
                        </field>
                        <field name="reference_data_link" optional="true">
                            <doc>
                                 Link to the NeXus file which describes the reference data if a
                                 reference measurement for window correction was performed.
                                 Ideally, the reference measurement was performed on a reference
                                 sample and on the same sample, and using the same conditions as
                                 for the actual measurement with and without windows. It should
                                 have been conducted as close in time to the actual measurement
                                 as possible.
                            </doc>
                        </field>
                    </group>
                    <field name="material" type="NX_CHAR">
                        <doc>
                             The material of the window.
                        </doc>
                        <enumeration>
                            <item value="quartz"/>
                            <item value="diamond"/>
                            <item value="calcium fluoride"/>
                            <item value="zinc selenide"/>
                            <item value="thallium bromoiodide"/>
                            <item value="alkali halide compound"/>
                            <item value="Mylar"/>
                            <item value="other"/>
                        </enumeration>
                    </field>
                    <field name="other_material" type="NX_CHAR" optional="true">
                        <doc>
                             If you specified 'other' as material, decsribe here what it is.
                        </doc>
                    </field>
                    <field name="thickness" type="NX_FLOAT" units="NX_LENGTH">
                        <doc>
                             Thickness of the window.
                        </doc>
                    </field>
                    <field name="orientation_angle" type="NX_FLOAT" units="NX_ANGLE">
                        <doc>
                             Angle of the window normal (outer) vs. the substrate normal
                             (similar to the angle of incidence).
                        </doc>
                    </field>
                </group>
            </group>
        </group>
        <group type="NXsample">
            <doc>
                 Properties of the sample, such as sample type, layer structure,
                 chemical formula, atom types, its history etc.
                 Information about the sample stage and sample environment should be
                 described in ENTRY/INSTRUMENT/sample_stage.
            </doc>
            <field name="sample_name">
                <doc>
                     Descriptive name of the sample
                </doc>
            </field>
            <field name="sample_type">
                <doc>
                     Specify the type of sample, e.g. thin film, single crystal etc.
                </doc>
                <enumeration>
                    <item value="thin film"/>
                    <item value="single crystal"/>
                    <item value="poly crystal"/>
                    <item value="single layer"/>
                    <item value="multi layer"/>
                </enumeration>
            </field>
            <field name="layer_structure">
                <doc>
                     Qualitative description of the layer structure for the sample,
                     starting with the top layer (i.e. the one on the front surface, on
                     which the light incident), e.g. native oxide/bulk substrate, or
                     Si/native oxide/thermal oxide/polymer/peptide.
                </doc>
            </field>
            <field name="chemical_formula">
                <doc>
                     Chemical formula of the sample. Use the Hill system (explained here:
                     https://en.wikipedia.org/wiki/Chemical_formula#Hill_system) to write
                     the chemical formula. In case the sample consists of several layers,
                     this should be a list of the chemical formulas of the individual
                     layers, where the first entry is the chemical formula of the top
                     layer (the one on the front surface, on which the light incident).
                     The order must be consistent with layer_structure
                </doc>
            </field>
            <field name="atom_types">
                <doc>
                     List of comma-separated elements from the periodic table that are
                     contained in the sample. If the sample substance has multiple
                     components, all elements from each component must be included in
                     'atom_types'.
                </doc>
            </field>
            <field name="sample_history">
                <doc>
                     Ideally, a reference to the location or a unique (globally
                     persistent) identifier (e.g.) of e.g. another file which gives
                     as many as possible details of the material, its microstructure,
                     and its thermo-chemo-mechanical processing/preparation history.
                     In the case that such a detailed history of the sample is not
                     available, use this field as a free-text description to specify
                     details of the sample and its preparation.
                </doc>
            </field>
            <field name="preparation_date" type="NX_DATE_TIME" recommended="true">
                <doc>
                     ISO8601 date with time zone (UTC offset) specified.
                </doc>
            </field>
            <field name="substrate" recommended="true">
                <doc>
                     Description of the substrate.
                </doc>
            </field>
            <field name="sample_orientation" optional="true">
                <doc>
                     Specify the sample orientation.
                </doc>
            </field>
        </group>
        <group name="data_collection" type="NXprocess">
            <doc>
                 Measured data, data errors, and varied parameters. If reference data
                 were measured they should be considered a separate experiment and a
                 link to its NeXus file should be added in reference_data_link.
            </doc>
            <field name="data_identifier" type="NX_NUMBER">
                <doc>
                     An identifier to correlate data to the experimental conditions,
                     if several were used in this measurement; typically an index of 0-N.
                </doc>
            </field>
            <field name="data_type">
                <doc>
                     Select which type of data was recorded, for example intensity,
                     reflectivity, transmittance, Psi and Delta etc.
                     It is possible to have multiple selections. The enumeration list
                     depends on the type of experiment and may differ for different
                     application definitions.
                </doc>
                <enumeration>
                    <item value="intensity"/>
                    <item value="reflectivity"/>
                    <item value="transmittance"/>
                    <item value="Psi/Delta"/>
                    <item value="tan(Psi)/cos(Delta)"/>
                    <item value="Mueller matrix"/>
                    <item value="Jones matrix"/>
                    <item value="N/C/S"/>
                    <item value="raw data"/>
                </enumeration>
            </field>
            <!--This should be a required field, but is set to 'optional' for the moment-->
            <field name="NAME_spectrum" type="NX_FLOAT" optional="true" units="NX_ANY">
                <doc>
                     Spectral values (e.g. wavelength or energy) used for the measurement.
                     An array of 1 or more elements. Length defines N_spectrum. Replace
                     'SPECTRUM' by the physical quantity that is used, e.g. wavelength.
                </doc>
                <dimensions rank="1">
                    <dim index="1" value="N_spectrum"/>
                </dimensions>
                <attribute name="units" optional="true">
                    <doc>
                         If applicable, change 'unit: NX_ANY' to the appropriate NXDL unit.
                         If the unit of the measured data is not covered by NXDL units state
                         here which unit was used.
                    </doc>
                </attribute>
            </field>
            <field name="measured_data" type="NX_FLOAT" units="NX_ANY">
                <doc>
                     Resulting data from the measurement, described by 'data_type'.
                     
                     The first dimension is defined by the number of measurements taken,
                     (N_measurements). The instructions on how to order the values
                     contained in the parameter vectors given in the doc string of
                     INSTRUMENT/sample_stage/environment_conditions/PARAMETER/values,
                     define the N_measurements parameter sets. For example, if the
                     experiment was performed at three different temperatures
                     (T1, T2, T3), two different pressures (p1, p2) and two different
                     angles of incidence (a1, a2), the first measurement was taken at the
                     parameters {a1,p1,T1}, the second measurement at {a1,p1,T2} etc.
                </doc>
                <dimensions rank="3">
                    <dim index="1" value="N_measurements"/>
                    <dim index="2" value="N_observables"/>
                    <dim index="3" value="N_spectrum"/>
                </dimensions>
                <attribute name="units" optional="true">
                    <doc>
                         If applicable, change 'unit: NX_ANY' to the appropriate NXDL unit.
                         If the unit of the measured data is not covered by NXDL units state
                         here which unit was used.
                    </doc>
                </attribute>
            </field>
            <field name="measured_data_errors" type="NX_FLOAT" optional="true" units="NX_ANY">
                <doc>
                     Specified uncertainties (errors) of the data described by 'data_type'
                     and provided in 'measured_data'.
                </doc>
                <dimensions rank="3">
                    <dim index="1" value="N_measurements"/>
                    <dim index="2" value="N_observables"/>
                    <dim index="3" value="N_spectrum"/>
                </dimensions>
                <attribute name="units" optional="true">
                    <doc>
                         If applicable, change 'unit: NX_ANY' to the appropriate NXDL unit.
                         If the unit of the measured data is not covered by NXDL units state
                         here which unit was used.
                    </doc>
                </attribute>
            </field>
            <field name="varied_parameter_link" optional="true">
                <doc>
                     List of links to the values of the sensors. Add a link for each
                     varied parameter (i.e. for each sensor).
                </doc>
                <dimensions rank="1">
                    <dim index="1" value="N_sensors"/>
                </dimensions>
            </field>
            <field name="reference_data_link" optional="true">
                <doc>
                     Link to the NeXus file which describes the reference data if a
                     reference measurement was performed. Ideally, the reference
                     measurement was performed using the same conditions as the actual
                     measurement and should be as close in time to the actual measurement
                     as possible.
                </doc>
            </field>
            <group name="data_software" type="NXprocess" optional="true">
                <field name="program">
                    <doc>
                         Commercial or otherwise defined given name of the program that was
                         used to generate the result file(s) with measured data and/or
                         metadata (in most cases, this is the same as INSTRUMENT/software).
                         If home written, one can provide the actual steps in the NOTE
                         subfield here.
                    </doc>
                </field>
                <field name="version">
                    <doc>
                         Either version with build number, commit hash, or description of a
                         (online) repository where the source code of the program and build
                         instructions can be found so that the program can be configured in
                         such a way that result files can be created ideally in a
                         deterministic manner.
                    </doc>
                </field>
                <attribute name="url" optional="true">
                    <doc>
                         Website of the software.
                    </doc>
                </attribute>
            </group>
            <group type="NXdata" optional="true">
                <doc>
                     A plot of the multi-dimensional data array provided in
                     ENTRY/data/measured_data.
                </doc>
                <attribute name="axes">
                    <doc>
                         Spectrum, i.e. x-axis of the data (e.g. wavelength, energy etc.)
                    </doc>
                </attribute>
            </group>
        </group>
        <group name="derived_parameters" type="NXprocess" optional="true">
            <doc>
                 Parameters that are derived from the measured data.
            </doc>
            <field name="depolarization" type="NX_NUMBER" optional="true" units="NX_UNITLESS">
                <doc>
                     Light loss due to depolarization as a value in [0-1].
                </doc>
                <dimensions rank="3">
                    <dim index="1" value="N_measurements"/>
                    <dim index="2" value="1"/>
                    <dim index="3" value="N_spectrum"/>
                </dimensions>
            </field>
            <field name="Jones_quality_factor" type="NX_NUMBER" optional="true" units="NX_UNITLESS">
                <doc>
                     Jones quality factor.
                </doc>
                <dimensions rank="3">
                    <dim index="1" value="N_measurements"/>
                    <dim index="2" value="1"/>
                    <dim index="3" value="N_spectrum"/>
                </dimensions>
            </field>
            <field name="reflectivity" type="NX_NUMBER" optional="true" units="NX_UNITLESS">
                <doc>
                     Reflectivity.
                </doc>
                <dimensions rank="3">
                    <dim index="1" value="N_measurements"/>
                    <dim index="2" value="1"/>
                    <dim index="3" value="N_spectrum"/>
                </dimensions>
            </field>
            <field name="transmittance" type="NX_NUMBER" optional="true" units="NX_UNITLESS">
                <doc>
                     Transmittance.
                </doc>
                <dimensions rank="3">
                    <dim index="1" value="N_measurements"/>
                    <dim index="2" value="1"/>
                    <dim index="3" value="N_spectrum"/>
                </dimensions>
            </field>
            <group name="ANALYSIS_program" type="NXprocess" optional="true">
                <field name="program">
                    <doc>
                         Commercial or otherwise defined given name of the program that was
                         used to generate or calculate the derived parameters.
                         If home written, one can provide the actual steps in the NOTE
                         subfield here.
                    </doc>
                </field>
                <field name="version">
                    <doc>
                         Either version with build number, commit hash, or description of a
                         (online) repository where the source code of the program and build
                         instructions can be found so that the program can be configured in
                         such a way that result files can be created ideally in a
                         deterministic manner.
                    </doc>
                </field>
            </group>
        </group>
        <group name="plot" type="NXdata">
            <doc>
                 A default view of the data provided in ENTRY/data_collection/measured_data. This
                 should be the part of the data set which provides the most suitable
                 representation of the data.
            </doc>
            <attribute name="axes">
                <doc>
                     Spectrum, i.e. x-axis of the data (e.g. wavelength, energy etc.)
                </doc>
            </attribute>
        </group>
    </group>
</definition>