Laser initialization in PICMI: allow negative focal distance and t_pe…

…ak (ECP-WarpX#5164)

* PICMI: allow negative focal distance and t_peak

* Update calculation of the normal vector

Python/pywarpx/picmi.py

@@ -1986,22 +1986,23 @@ def laser_antenna_initialize_inputs(self, laser):
                 "specified antenna normal."
             )
         self.normal_vector = laser.laser.direction  # The plane normal direction
+        # Ensure the normal vector is a unit vector
+        self.normal_vector /= np.linalg.norm(self.normal_vector)
         if isinstance(laser, GaussianLaser):
-            # Focal distance from the antenna (in meters)
-            laser.laser.profile_focal_distance = np.sqrt(
-                (laser.focal_position[0] - self.position[0]) ** 2
-                + (laser.focal_position[1] - self.position[1]) ** 2
-                + (laser.focal_position[2] - self.position[2]) ** 2
+            # Focal displacement from the antenna (in meters)
+            laser.laser.profile_focal_distance = (
+                (laser.focal_position[0] - self.position[0]) * self.normal_vector[0]
+                + (laser.focal_position[1] - self.position[1]) * self.normal_vector[1]
+                + (laser.focal_position[2] - self.position[2]) * self.normal_vector[2]
             )
             # The time at which the laser reaches its peak (in seconds)
             laser.laser.profile_t_peak = (
-                np.sqrt(
-                    (self.position[0] - laser.centroid_position[0]) ** 2
-                    + (self.position[1] - laser.centroid_position[1]) ** 2
-                    + (self.position[2] - laser.centroid_position[2]) ** 2
-                )
-                / constants.c
-            )
+                (self.position[0] - laser.centroid_position[0]) * self.normal_vector[0]
+                + (self.position[1] - laser.centroid_position[1])
+                * self.normal_vector[1]
+                + (self.position[2] - laser.centroid_position[2])
+                * self.normal_vector[2]
+            ) / constants.c
 
 
 class LoadInitialField(picmistandard.PICMI_LoadGriddedField):