add initial beam splitter, flesh out Photons model a bit more

js/photons/model/PhotonDetector.ts

@@ -16,8 +16,6 @@ import quantumMeasurement from '../../quantumMeasurement.js';
 
 type SelfOptions = EmptySelfOptions;
 type PhotonDetectorOptions = SelfOptions & PickRequired<PhetioObjectOptions, 'tandem'>;
-
-// constants
 export type DetectionDirection = ( [ 'up', 'down' ] )[number];
 
 export default class PhotonDetector {

js/photons/model/PhotonsModel.ts

@@ -4,28 +4,34 @@
  * PhotonsModel is the primary model class for the Photons screen.  It manages the general model state and behavior for
  * the photons that travel from the source to the detectors.
  *
- * Part of what this model does is position photons in two-dimensional space.  This space is set up to center on the
+ * Part of what this model does is move photons in two-dimensional space.  This space is set up to center on the
  * polarizing beam splitter, which is at the center of the screen.  The x-axis is horizontal and the y-axis is vertical.
- * Units are in meters.
+ * Units are in meters.  The photons are emitted from a source, travel to the polarizing beam splitter, and then are
+ * either reflected or transmitted.  The photons are then detected by two photon detectors.
  *
  * @author John Blanco, PhET Interactive Simulations
  */
 
 import NumberProperty from '../../../../axon/js/NumberProperty.js';
+import Range from '../../../../dot/js/Range.js';
 import Vector2 from '../../../../dot/js/Vector2.js';
 import TModel from '../../../../joist/js/TModel.js';
 import { EmptySelfOptions } from '../../../../phet-core/js/optionize.js';
 import PickRequired from '../../../../phet-core/js/types/PickRequired.js';
 import { PhetioObjectOptions } from '../../../../tandem/js/PhetioObject.js';
 import quantumMeasurement from '../../quantumMeasurement.js';
 import PhotonDetector from './PhotonDetector.js';
+import PolarizingBeamSplitter from './PolarizingBeamSplitter.js';
 
 type SelfOptions = EmptySelfOptions;
 type QuantumMeasurementModelOptions = SelfOptions & PickRequired<PhetioObjectOptions, 'tandem'>;
 
 export default class PhotonsModel implements TModel {
 
-  // The angle of polarization for the polarizing beam splitter.
+  // The polarizing beam splitter that the photons will encounter.
+  public readonly polarizingBeamSplitter: PolarizingBeamSplitter;
+
+  // The angle of polarization for the polarizing beam splitter, in degrees.  Zero is horizontal and 90 is vertical.
   public readonly photonPolarizationAngleProperty: NumberProperty;
 
   // photon detectors
@@ -34,7 +40,12 @@ export default class PhotonsModel implements TModel {
 
   public constructor( providedOptions: QuantumMeasurementModelOptions ) {
 
-    this.photonPolarizationAngleProperty = new NumberProperty( 0, {
+    this.polarizingBeamSplitter = new PolarizingBeamSplitter( new Vector2( 0, 0 ), {
+      tandem: providedOptions.tandem.createTandem( 'polarizingBeamSplitter' )
+    } );
+
+    this.photonPolarizationAngleProperty = new NumberProperty( 45, {
+      range: new Range( 0, 90 ),
       tandem: providedOptions.tandem.createTandem( 'photonPolarizationAngleProperty' )
     } );
 

js/photons/model/PolarizingBeamSplitter.ts

@@ -0,0 +1,61 @@
+// Copyright 2024, University of Colorado Boulder
+
+/**
+ * PolarizingBeamSplitter is a model element that represents a device that splits a beam of photons into two beams based
+ * on the polarization of the photons.
+ *
+ * @author John Blanco, PhET Interactive Simulations
+ */
+
+import NumberProperty from '../../../../axon/js/NumberProperty.js';
+import Property from '../../../../axon/js/Property.js';
+import Vector2 from '../../../../dot/js/Vector2.js';
+import { Line } from '../../../../kite/js/imports.js';
+import { EmptySelfOptions } from '../../../../phet-core/js/optionize.js';
+import PickRequired from '../../../../phet-core/js/types/PickRequired.js';
+import { PhetioObjectOptions } from '../../../../tandem/js/PhetioObject.js';
+import quantumMeasurement from '../../quantumMeasurement.js';
+
+type SelfOptions = EmptySelfOptions;
+type PolarizingBeamSplitterOptions = SelfOptions & PickRequired<PhetioObjectOptions, 'tandem'>;
+
+export type PresetPolarizationDirections = ( [ 'vertical', 'horizontal', 'fortyFiveDegrees', 'custom' ] )[number];
+
+// constants
+const WIDTH = 0.1; // the width, in meters, of the beam splitter
+const ROTATIONAL_ANGLE = Math.PI / 4; // the angle at which the beam splitter is rotated, in radians, zero is horizontal
+
+export default class PolarizingBeamSplitter {
+
+  // The position of the center of the beam splitter in two-dimensional space.  Units are in meters.
+  public readonly centerPosition: Vector2;
+
+  // A line in model space that represents the position of the beam splitter.
+  public readonly positionalLine: Line;
+
+  // The direction of polarization that the beam splitter is set to.  This can be one of the preset directions or a
+  // custom angle.
+  public readonly presetPolarizationDirectionProperty: Property<PresetPolarizationDirections>;
+
+  // The custom angle at which the beam splitter is set, in degrees.  This is only used when the preset direction is
+  // "custom".
+  public readonly customPolarizationAngleProperty: NumberProperty;
+
+  public constructor( centerPosition: Vector2, providedOptions: PolarizingBeamSplitterOptions ) {
+    this.centerPosition = centerPosition;
+
+    // Initialize the line that represents the position of the beam splitter in the model.
+    const endpoint1 = centerPosition.plusXY( WIDTH / 2, 0 ).rotated( ROTATIONAL_ANGLE );
+    const endpoint2 = centerPosition.plusXY( -WIDTH / 2, 0 ).rotated( ROTATIONAL_ANGLE );
+    this.positionalLine = new Line( endpoint1, endpoint2 );
+
+    this.presetPolarizationDirectionProperty = new Property<PresetPolarizationDirections>( 'fortyFiveDegrees', {
+      tandem: providedOptions.tandem.createTandem( 'presetPolarizationDirectionProperty' )
+    } );
+    this.customPolarizationAngleProperty = new NumberProperty( 45, {
+      tandem: providedOptions.tandem.createTandem( 'customPolarizationAngleProperty' )
+    } );
+  }
+}
+
+quantumMeasurement.register( 'PolarizingBeamSplitter', PolarizingBeamSplitter );