remove explicit interaction type 'none' and use absence of explicit i…

…nteractions for this case, see #65

js/photons/model/Mirror.ts

@@ -41,6 +41,9 @@ export default class Mirror implements TPhotonInteraction {
     this.mirrorSurfaceLine = new Line( endpoint1, endpoint2 );
   }
 
+  /**
+   * Test for interaction between the provided photon and this mirror.
+   */
   public testForPhotonInteraction( photon: Photon, dt: number ): Map<PhotonMotionState, PhotonInteractionTestResult> {
 
     const mapOfStatesToInteractions = new Map<PhotonMotionState, PhotonInteractionTestResult>();
@@ -66,9 +69,6 @@ export default class Mirror implements TPhotonInteraction {
           }
         } );
       }
-      else {
-        mapOfStatesToInteractions.set( photonState, { interactionType: 'none' } );
-      }
     } );
 
     return mapOfStatesToInteractions;

js/photons/model/PhotonDetector.ts

@@ -89,6 +89,9 @@ export default class PhotonDetector implements TPhotonInteraction {
     } );
   }
 
+  /**
+   * Test for interaction between the provided photon and this detector.
+   */
   public testForPhotonInteraction( photon: Photon, dt: number ): Map<PhotonMotionState, PhotonInteractionTestResult> {
 
     const mapOfStatesToInteractions = new Map<PhotonMotionState, PhotonInteractionTestResult>();
@@ -103,31 +106,27 @@ export default class PhotonDetector implements TPhotonInteraction {
         dt
       );
 
-      // Assume no interaction until proven otherwise.
-      let interaction: PhotonInteractionTestResult = { interactionType: 'none' };
-
       // This is where the wave function collapses!
       if ( photonIntersectionPoint !== null ) {
 
         // Evaluate the detection result based on the probability of the photon actually being here.
         if ( dotRandom.nextDouble() < photonState.probability ) {
+
+          // The photon is being absorbed by the detector.
           photon.setMotionStateProbability( photonState, 1 );
-          photonState.probability = 1; // the photon is detected!
-          interaction = { interactionType: 'absorbed' };
+          this.detectionCountProperty.value = Math.min( this.detectionCountProperty.value + 1, COUNT_RANGE.max );
+          this.detectionRateProperty.countEvent();
+
+          // Indicate that the photon was absorbed.
+          mapOfStatesToInteractions.set( photonState, { interactionType: 'absorbed' } );
         }
         else {
 
-          // If the photon is not detected. This state probability goes to 0%, which will make the other state 100%.
+          // If this photon state does not trigger the detector the associated probability goes to 0%, which will make
+          // the other state's probability 100%.
           photon.setMotionStateProbability( photonState, 0 );
         }
       }
-
-      if ( interaction.interactionType === 'absorbed' ) {
-        this.detectionCountProperty.value = Math.min( this.detectionCountProperty.value + 1, COUNT_RANGE.max );
-        this.detectionRateProperty.countEvent();
-      }
-
-      mapOfStatesToInteractions.set( photonState, interaction );
     } );
 
     return mapOfStatesToInteractions;

js/photons/model/PhotonsModel.ts

@@ -25,7 +25,7 @@ import PhotonsExperimentSceneModel from './PhotonsExperimentSceneModel.js';
 type SelfOptions = EmptySelfOptions;
 type PhotonsModelOptions = SelfOptions & PickRequired<PhetioObjectOptions, 'tandem'>;
 
-export const PhotonInteractionTypeValues = [ 'none', 'absorbed', 'reflected', 'split' ] as const;
+export const PhotonInteractionTypeValues = [ 'absorbed', 'reflected', 'split' ] as const;
 export type PhotonInteractionTypes = ( typeof PhotonInteractionTypeValues )[number];
 export type PhotonInteractionTestResult = {
   interactionType: PhotonInteractionTypes;

js/photons/model/PolarizingBeamSplitter.ts

@@ -50,6 +50,9 @@ export default class PolarizingBeamSplitter implements TPhotonInteraction {
     this.polarizingSurfaceLine = new Line( endpoint1, endpoint2 );
   }
 
+  /**
+   * Test for photon interactions with the beam splitter.
+   */
   public testForPhotonInteraction( photon: Photon, dt: number ): Map<PhotonMotionState, PhotonInteractionTestResult> {
 
     const mapOfStatesToInteractions = new Map<PhotonMotionState, PhotonInteractionTestResult>();
@@ -64,8 +67,6 @@ export default class PolarizingBeamSplitter implements TPhotonInteraction {
         dt
       );
 
-      let interaction: PhotonInteractionTestResult = { interactionType: 'none' };
-
       if ( photonIntersectionPoint !== null ) {
 
         // Calculate the probability of reflection based on the custom angle according to Malus's Law
@@ -78,20 +79,20 @@ export default class PolarizingBeamSplitter implements TPhotonInteraction {
           if ( dotRandom.nextDouble() <= probabilityOfReflection ) {
 
             // The photon is being reflected by the beam splitter.  The only direction supported currently is up.
-            interaction = {
+            mapOfStatesToInteractions.set( photonState, {
               interactionType: 'reflected',
               reflectionInfo: {
                 reflectionPoint: photonIntersectionPoint,
                 reflectionDirection: UP
               }
-            };
+            } );
           }
         }
         else {
 
           // This is the quantum case where the photon is split into a superposition of states until observed by one of
           // the detectors.
-          interaction = {
+          mapOfStatesToInteractions.set( photonState, {
             interactionType: 'split',
             splitInfo: {
               splitPoint: photonIntersectionPoint,
@@ -106,11 +107,9 @@ export default class PolarizingBeamSplitter implements TPhotonInteraction {
                 }
               ]
             }
-          };
+          } );
         }
       }
-
-      mapOfStatesToInteractions.set( photonState, interaction );
     } );
 
     return mapOfStatesToInteractions;

js/photons/model/TPhotonInteraction.ts

@@ -11,5 +11,14 @@ import { PhotonMotionState } from './PhotonMotionState.js';
 import { PhotonInteractionTestResult } from './PhotonsModel.js';
 
 export type TPhotonInteraction = {
+
+  /**
+   * Test for photon interactions with the object that implements this interface.  This returns a map of photon states
+   * to interactions.  If a photon state is not in the map, no interaction is detected for that state.
+   *
+   * @param photon - The photon that is being tested for interaction.
+   * @param dt - The time step for the test, in seconds.
+   * @returns A map of motion states to the results of the interaction tests.
+   */
   testForPhotonInteraction( photon: Photon, dt: number ): Map<PhotonMotionState, PhotonInteractionTestResult>;
 };