diff --git a/src/common/model/blockers/LineBlocker.ts b/src/common/model/blockers/LineBlocker.ts
index f030a8e..bd7d451 100644
--- a/src/common/model/blockers/LineBlocker.ts
+++ b/src/common/model/blockers/LineBlocker.ts
@@ -4,8 +4,8 @@
  * A line-segment blocker that absorbs all rays hitting it.
  */
 
-import { BaseElement } from "../optics/BaseElement.js";
-import { dot, type Point, point, raySegmentIntersection, segment, segmentNormal } from "../optics/Geometry.js";
+import { BaseSegmentElement } from "../optics/BaseSegmentElement.js";
+import { type Point } from "../optics/Geometry.js";
 import type {
   ElementCategory,
   IntersectionResult,
@@ -13,27 +13,12 @@ import type {
   SimulationRay,
 } from "../optics/OpticsTypes.js";
 
-export class LineBlocker extends BaseElement {
+export class LineBlocker extends BaseSegmentElement {
   public readonly type = "Blocker";
   public readonly category: ElementCategory = "blocker";
 
-  public p1: Point;
-  public p2: Point;
-
   public constructor(p1: Point, p2: Point) {
-    super();
-    this.p1 = p1;
-    this.p2 = p2;
-  }
-
-  public override checkRayIntersection(ray: SimulationRay): IntersectionResult | null {
-    const hit = raySegmentIntersection(ray.origin, ray.direction, segment(this.p1, this.p2));
-    if (!hit) {
-      return null;
-    }
-    const normal = segmentNormal(segment(this.p1, this.p2));
-    const facingRay = dot(normal, ray.direction) < 0 ? normal : point(-normal.x, -normal.y);
-    return { point: hit.point, t: hit.t, element: this, normal: facingRay };
+    super(p1, p2);
   }
 
   public override onRayIncident(_ray: SimulationRay, _intersection: IntersectionResult): RayInteractionResult {
diff --git a/src/common/model/glass/IdealLens.ts b/src/common/model/glass/IdealLens.ts
index 3d9a3b4..b9cd74e 100644
--- a/src/common/model/glass/IdealLens.ts
+++ b/src/common/model/glass/IdealLens.ts
@@ -8,7 +8,7 @@
  */
 
 import { DEFAULT_FOCAL_LENGTH } from "../../../OpticsLabConstants.js";
-import { BaseElement } from "../optics/BaseElement.js";
+import { BaseSegmentElement } from "../optics/BaseSegmentElement.js";
 import {
   normalize,
   type Point,
@@ -25,21 +25,19 @@ import type {
   SimulationRay,
 } from "../optics/OpticsTypes.js";
 
-export class IdealLens extends BaseElement {
+export class IdealLens extends BaseSegmentElement {
   public readonly type = "IdealLens";
   public readonly category: ElementCategory = "glass";
 
-  public p1: Point;
-  public p2: Point;
   public focalLength: number;
 
   public constructor(p1: Point, p2: Point, focalLength = DEFAULT_FOCAL_LENGTH) {
-    super();
-    this.p1 = p1;
-    this.p2 = p2;
+    super(p1, p2);
     this.focalLength = focalLength;
   }
 
+  // IdealLens uses an unflipped normal so that the lens equation works correctly
+  // for rays incident from either side.
   public override checkRayIntersection(ray: SimulationRay): IntersectionResult | null {
     const hit = raySegmentIntersection(ray.origin, ray.direction, segment(this.p1, this.p2));
     if (!hit) {
diff --git a/src/common/model/gratings/ReflectionGrating.ts b/src/common/model/gratings/ReflectionGrating.ts
index 2cf60c9..528f84d 100644
--- a/src/common/model/gratings/ReflectionGrating.ts
+++ b/src/common/model/gratings/ReflectionGrating.ts
@@ -11,16 +11,8 @@
  *  - dutyCycle:    slit-width to line-spacing ratio (0–1), controls order intensities
  */
 
-import { BaseElement } from "../optics/BaseElement.js";
-import {
-  dot,
-  normalize,
-  type Point,
-  point,
-  raySegmentIntersection,
-  segment,
-  segmentNormal,
-} from "../optics/Geometry.js";
+import { BaseSegmentElement } from "../optics/BaseSegmentElement.js";
+import { dot, normalize, type Point, point } from "../optics/Geometry.js";
 import type {
   ElementCategory,
   IntersectionResult,
@@ -33,36 +25,21 @@ const DEFAULT_WAVELENGTH_NM = 532;
 /** Maximum diffraction order to compute. */
 const MAX_ORDER = 10;
 
-export class ReflectionGrating extends BaseElement {
+export class ReflectionGrating extends BaseSegmentElement {
   public readonly type = "ReflectionGrating";
   public readonly category: ElementCategory = "mirror";
 
-  public p1: Point;
-  public p2: Point;
   /** Groove density in lines per mm. */
   public linesDensity: number;
   /** Slit-width / line-spacing ratio (0–1). */
   public dutyCycle: number;
 
   public constructor(p1: Point, p2: Point, linesDensity = 600, dutyCycle = 0.5) {
-    super();
-    this.p1 = p1;
-    this.p2 = p2;
+    super(p1, p2);
     this.linesDensity = linesDensity;
     this.dutyCycle = dutyCycle;
   }
 
-  public override checkRayIntersection(ray: SimulationRay): IntersectionResult | null {
-    const hit = raySegmentIntersection(ray.origin, ray.direction, segment(this.p1, this.p2));
-    if (!hit) {
-      return null;
-    }
-    const normal = segmentNormal(segment(this.p1, this.p2));
-    // Orient normal to face incoming ray
-    const facingRay = dot(normal, ray.direction) < 0 ? normal : point(-normal.x, -normal.y);
-    return { point: hit.point, t: hit.t, element: this, normal: facingRay };
-  }
-
   public override onRayIncident(ray: SimulationRay, intersection: IntersectionResult): RayInteractionResult {
     const n = intersection.normal;
     const wavelengthNm = ray.wavelength ?? DEFAULT_WAVELENGTH_NM;
diff --git a/src/common/model/gratings/TransmissionGrating.ts b/src/common/model/gratings/TransmissionGrating.ts
index 882de8a..db87cc7 100644
--- a/src/common/model/gratings/TransmissionGrating.ts
+++ b/src/common/model/gratings/TransmissionGrating.ts
@@ -11,16 +11,8 @@
  *  - dutyCycle:    slit-width to line-spacing ratio (0–1), controls order intensities
  */
 
-import { BaseElement } from "../optics/BaseElement.js";
-import {
-  dot,
-  normalize,
-  type Point,
-  point,
-  raySegmentIntersection,
-  segment,
-  segmentNormal,
-} from "../optics/Geometry.js";
+import { BaseSegmentElement } from "../optics/BaseSegmentElement.js";
+import { dot, normalize, type Point, point } from "../optics/Geometry.js";
 import type {
   ElementCategory,
   IntersectionResult,
@@ -33,36 +25,21 @@ const DEFAULT_WAVELENGTH_NM = 532;
 /** Maximum diffraction order to compute. */
 const MAX_ORDER = 10;
 
-export class TransmissionGrating extends BaseElement {
+export class TransmissionGrating extends BaseSegmentElement {
   public readonly type = "TransmissionGrating";
   public readonly category: ElementCategory = "glass";
 
-  public p1: Point;
-  public p2: Point;
   /** Groove density in lines per mm. */
   public linesDensity: number;
   /** Slit-width / line-spacing ratio (0–1). */
   public dutyCycle: number;
 
   public constructor(p1: Point, p2: Point, linesDensity = 600, dutyCycle = 0.5) {
-    super();
-    this.p1 = p1;
-    this.p2 = p2;
+    super(p1, p2);
     this.linesDensity = linesDensity;
     this.dutyCycle = dutyCycle;
   }
 
-  public override checkRayIntersection(ray: SimulationRay): IntersectionResult | null {
-    const hit = raySegmentIntersection(ray.origin, ray.direction, segment(this.p1, this.p2));
-    if (!hit) {
-      return null;
-    }
-    const normal = segmentNormal(segment(this.p1, this.p2));
-    // Orient normal to face incoming ray
-    const facingRay = dot(normal, ray.direction) < 0 ? normal : point(-normal.x, -normal.y);
-    return { point: hit.point, t: hit.t, element: this, normal: facingRay };
-  }
-
   public override onRayIncident(ray: SimulationRay, intersection: IntersectionResult): RayInteractionResult {
     const n = intersection.normal;
     const wavelengthNm = ray.wavelength ?? DEFAULT_WAVELENGTH_NM;
diff --git a/src/common/model/index.ts b/src/common/model/index.ts
index 27e0698..4744417 100644
--- a/src/common/model/index.ts
+++ b/src/common/model/index.ts
@@ -35,6 +35,7 @@ export { ParabolicMirror } from "./mirrors/ParabolicMirror.js";
 // ── Mirrors ──────────────────────────────────────────────────────────────────
 export { SegmentMirror } from "./mirrors/SegmentMirror.js";
 export { BaseElement } from "./optics/BaseElement.js";
+export { BaseSegmentElement } from "./optics/BaseSegmentElement.js";
 // ── Core types & geometry ────────────────────────────────────────────────────
 export type { Circle, Line, Point, Segment } from "./optics/Geometry.js";
 export {
diff --git a/src/common/model/mirrors/BeamSplitterElement.ts b/src/common/model/mirrors/BeamSplitterElement.ts
index ca954a2..256859c 100644
--- a/src/common/model/mirrors/BeamSplitterElement.ts
+++ b/src/common/model/mirrors/BeamSplitterElement.ts
@@ -7,16 +7,8 @@
  * in the original direction.
  */
 
-import { BaseElement } from "../optics/BaseElement.js";
-import {
-  dot,
-  normalize,
-  type Point,
-  point,
-  raySegmentIntersection,
-  segment,
-  segmentNormal,
-} from "../optics/Geometry.js";
+import { BaseSegmentElement } from "../optics/BaseSegmentElement.js";
+import { dot, normalize, type Point, point } from "../optics/Geometry.js";
 import type {
   ElementCategory,
   IntersectionResult,
@@ -24,32 +16,18 @@ import type {
   SimulationRay,
 } from "../optics/OpticsTypes.js";
 
-export class BeamSplitterElement extends BaseElement {
+export class BeamSplitterElement extends BaseSegmentElement {
   public readonly type = "BeamSplitter";
   public readonly category: ElementCategory = "mirror";
 
-  public p1: Point;
-  public p2: Point;
   /** Fraction of brightness transmitted (0..1). The rest is reflected. */
   public transRatio: number;
 
   public constructor(p1: Point, p2: Point, transRatio = 0.5) {
-    super();
-    this.p1 = p1;
-    this.p2 = p2;
+    super(p1, p2);
     this.transRatio = transRatio;
   }
 
-  public override checkRayIntersection(ray: SimulationRay): IntersectionResult | null {
-    const hit = raySegmentIntersection(ray.origin, ray.direction, segment(this.p1, this.p2));
-    if (!hit) {
-      return null;
-    }
-    const normal = segmentNormal(segment(this.p1, this.p2));
-    const facingRay = dot(normal, ray.direction) < 0 ? normal : point(-normal.x, -normal.y);
-    return { point: hit.point, t: hit.t, element: this, normal: facingRay };
-  }
-
   public override onRayIncident(ray: SimulationRay, intersection: IntersectionResult): RayInteractionResult {
     const n = intersection.normal;
     const d = ray.direction;
diff --git a/src/common/model/mirrors/IdealCurvedMirror.ts b/src/common/model/mirrors/IdealCurvedMirror.ts
index 075c8ba..4884c36 100644
--- a/src/common/model/mirrors/IdealCurvedMirror.ts
+++ b/src/common/model/mirrors/IdealCurvedMirror.ts
@@ -7,19 +7,16 @@
  */
 
 import { DEFAULT_FOCAL_LENGTH } from "../../../OpticsLabConstants.js";
-import { BaseElement } from "../optics/BaseElement.js";
+import { BaseSegmentElement } from "../optics/BaseSegmentElement.js";
 import {
   distanceSquared,
-  dot,
   line,
   linesIntersection,
   normalize,
   type Point,
   point,
-  raySegmentIntersection,
   segment,
   segmentMidpoint,
-  segmentNormal,
 } from "../optics/Geometry.js";
 import type {
   ElementCategory,
@@ -28,31 +25,17 @@ import type {
   SimulationRay,
 } from "../optics/OpticsTypes.js";
 
-export class IdealCurvedMirror extends BaseElement {
+export class IdealCurvedMirror extends BaseSegmentElement {
   public readonly type = "IdealMirror";
   public readonly category: ElementCategory = "mirror";
 
-  public p1: Point;
-  public p2: Point;
   public focalLength: number;
 
   public constructor(p1: Point, p2: Point, focalLength = DEFAULT_FOCAL_LENGTH) {
-    super();
-    this.p1 = p1;
-    this.p2 = p2;
+    super(p1, p2);
     this.focalLength = focalLength;
   }
 
-  public override checkRayIntersection(ray: SimulationRay): IntersectionResult | null {
-    const hit = raySegmentIntersection(ray.origin, ray.direction, segment(this.p1, this.p2));
-    if (!hit) {
-      return null;
-    }
-    const normal = segmentNormal(segment(this.p1, this.p2));
-    const facingRay = dot(normal, ray.direction) < 0 ? normal : point(-normal.x, -normal.y);
-    return { point: hit.point, t: hit.t, element: this, normal: facingRay };
-  }
-
   public override onRayIncident(ray: SimulationRay, intersection: IntersectionResult): RayInteractionResult {
     const ip = intersection.point;
     const center = segmentMidpoint(segment(this.p1, this.p2));
diff --git a/src/common/model/mirrors/SegmentMirror.ts b/src/common/model/mirrors/SegmentMirror.ts
index 95c6a2a..96d01ba 100644
--- a/src/common/model/mirrors/SegmentMirror.ts
+++ b/src/common/model/mirrors/SegmentMirror.ts
@@ -5,17 +5,8 @@
  * law of reflection: angle of incidence = angle of reflection.
  */
 
-import { BaseElement } from "../optics/BaseElement.js";
-import {
-  dot,
-  normalize,
-  type Point,
-  point,
-  raySegmentIntersection,
-  segment,
-  segmentNormal,
-  subtract,
-} from "../optics/Geometry.js";
+import { BaseSegmentElement } from "../optics/BaseSegmentElement.js";
+import { normalize, type Point, point, subtract } from "../optics/Geometry.js";
 import type {
   ElementCategory,
   IntersectionResult,
@@ -23,27 +14,12 @@ import type {
   SimulationRay,
 } from "../optics/OpticsTypes.js";
 
-export class SegmentMirror extends BaseElement {
+export class SegmentMirror extends BaseSegmentElement {
   public readonly type = "Mirror";
   public readonly category: ElementCategory = "mirror";
 
-  public p1: Point;
-  public p2: Point;
-
   public constructor(p1: Point, p2: Point) {
-    super();
-    this.p1 = p1;
-    this.p2 = p2;
-  }
-
-  public override checkRayIntersection(ray: SimulationRay): IntersectionResult | null {
-    const hit = raySegmentIntersection(ray.origin, ray.direction, segment(this.p1, this.p2));
-    if (!hit) {
-      return null;
-    }
-    const normal = segmentNormal(segment(this.p1, this.p2));
-    const facingRay = dot(normal, ray.direction) < 0 ? normal : point(-normal.x, -normal.y);
-    return { point: hit.point, t: hit.t, element: this, normal: facingRay };
+    super(p1, p2);
   }
 
   public override onRayIncident(ray: SimulationRay, intersection: IntersectionResult): RayInteractionResult {
diff --git a/src/common/model/optics/BaseSegmentElement.ts b/src/common/model/optics/BaseSegmentElement.ts
new file mode 100644
index 0000000..751f963
--- /dev/null
+++ b/src/common/model/optics/BaseSegmentElement.ts
@@ -0,0 +1,32 @@
+/**
+ * BaseSegmentElement.ts
+ *
+ * Abstract base class for optical elements defined by a line segment (p1, p2).
+ * Provides shared p1/p2 fields and a default checkRayIntersection that tests
+ * for a segment hit and returns a normal oriented toward the incoming ray.
+ */
+
+import { BaseElement } from "./BaseElement.js";
+import { dot, type Point, point, raySegmentIntersection, segment, segmentNormal } from "./Geometry.js";
+import type { IntersectionResult, SimulationRay } from "./OpticsTypes.js";
+
+export abstract class BaseSegmentElement extends BaseElement {
+  public p1: Point;
+  public p2: Point;
+
+  public constructor(p1: Point, p2: Point) {
+    super();
+    this.p1 = p1;
+    this.p2 = p2;
+  }
+
+  public override checkRayIntersection(ray: SimulationRay): IntersectionResult | null {
+    const hit = raySegmentIntersection(ray.origin, ray.direction, segment(this.p1, this.p2));
+    if (!hit) {
+      return null;
+    }
+    const normal = segmentNormal(segment(this.p1, this.p2));
+    const facingRay = dot(normal, ray.direction) < 0 ? normal : point(-normal.x, -normal.y);
+    return { point: hit.point, t: hit.t, element: this, normal: facingRay };
+  }
+}