diff --git a/Laser_utils.py b/Laser_utils.py
index 0af4c88ed419096a910bb2a75ed49de97695584c..157f387cf390107d52bf686ff7b5cbb05b0779ec 100644
--- a/Laser_utils.py
+++ b/Laser_utils.py
@@ -12,4 +12,16 @@ def positionToDelay(data, key, origin=0, invert = False, reflections=1):
     '''
     c_ = 299792458 *1e-9 # speed of light in mm/ps
     x = -1 if invert else 1
-    return 2*reflections*(data[key]-origin)*x/c_
\ No newline at end of file
+    return 2*reflections*(data[key]-origin)*x/c_
+    
+def degToRelPower(x, theta0=0):
+    ''' converts a half-wave plate position in degrees into relative power
+        between 0 and 1.
+        Inputs:
+            x: array-like positions of half-wave plate, in degrees
+            theta0: position for which relative power is zero
+            
+        Output:
+            array-like relative power
+    '''
+    return np.sin(2*(x-theta0)*np.pi/180)**2