From ef81bd46ac63c8ed59c15035132cae36b66d0684 Mon Sep 17 00:00:00 2001
From: Roy Smart <roytsmart@gmail.com>
Date: Sat, 20 Sep 2025 11:22:34 -0600
Subject: [PATCH 1/2] Modified `optika.sensors.absorbance()` to _not_ consider
 reflections from the non-illuminated side for performance reasons.

---
 optika/sensors/_materials/_materials.py | 47 ++++++++++++++++---------
 1 file changed, 31 insertions(+), 16 deletions(-)

diff --git a/optika/sensors/_materials/_materials.py b/optika/sensors/_materials/_materials.py
index 9b56eb9e..929f4b6f 100644
--- a/optika/sensors/_materials/_materials.py
+++ b/optika/sensors/_materials/_materials.py
@@ -126,29 +126,44 @@ def absorbance(
     if not isinstance(chemical_substrate, optika.chemicals.AbstractChemical):
         chemical_substrate = optika.chemicals.Chemical(chemical_substrate)
 
-    result = optika.materials.layer_absorbance(
-        index=1,
+    layer_oxide = optika.materials.Layer(
+        chemical=chemical_oxide,
+        thickness=thickness_oxide,
+        interface=optika.materials.profiles.ErfInterfaceProfile(
+            width=roughness_oxide,
+        ),
+    )
+
+    layer_substrate = optika.materials.Layer(
+        chemical=chemical_substrate,
+        thickness=thickness_substrate,
+        interface=optika.materials.profiles.ErfInterfaceProfile(
+            width=roughness_substrate,
+        ),
+    )
+
+    _, transmissivity_oxide = optika.materials.multilayer_efficiency(
         wavelength=wavelength,
         direction=direction,
         n=n,
         layers=[
-            optika.materials.Layer(
-                chemical=chemical_oxide,
-                thickness=thickness_oxide,
-                interface=optika.materials.profiles.ErfInterfaceProfile(
-                    width=roughness_oxide,
-                ),
-            ),
-            optika.materials.Layer(
-                chemical=chemical_substrate,
-                thickness=thickness_substrate,
-                interface=optika.materials.profiles.ErfInterfaceProfile(
-                    width=roughness_substrate,
-                ),
-            ),
+            layer_oxide,
+        ],
+        substrate=layer_substrate,
+    )
+
+    _, transmissivity_total = optika.materials.multilayer_efficiency(
+        wavelength=wavelength,
+        direction=direction,
+        n=n,
+        layers=[
+            layer_oxide,
+            layer_substrate,
         ],
     )
 
+    result = transmissivity_oxide - transmissivity_total
+
     return np.real(result)
 
 

From 65fd04eefbfd71c503a5a380092fd430805c8b20 Mon Sep 17 00:00:00 2001
From: Roy Smart <roytsmart@gmail.com>
Date: Sat, 20 Sep 2025 20:50:48 -0600
Subject: [PATCH 2/2] further improvements

---
 optika/sensors/_materials/_materials.py | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/optika/sensors/_materials/_materials.py b/optika/sensors/_materials/_materials.py
index 929f4b6f..a6d1b12e 100644
--- a/optika/sensors/_materials/_materials.py
+++ b/optika/sensors/_materials/_materials.py
@@ -152,15 +152,11 @@ def absorbance(
         substrate=layer_substrate,
     )
 
-    _, transmissivity_total = optika.materials.multilayer_efficiency(
-        wavelength=wavelength,
-        direction=direction,
-        n=n,
-        layers=[
-            layer_oxide,
-            layer_substrate,
-        ],
-    )
+    absorption = chemical_substrate.absorption(wavelength)
+
+    decay = np.exp(-absorption * thickness_substrate)
+
+    transmissivity_total = transmissivity_oxide * decay
 
     result = transmissivity_oxide - transmissivity_total