diff --git a/meanas/fdtd/misc.py b/meanas/fdtd/misc.py
index 3fb3371..1d90c32 100644
--- a/meanas/fdtd/misc.py
+++ b/meanas/fdtd/misc.py
@@ -156,11 +156,11 @@ def gaussian_beam(
     wz = numpy.sqrt(wz2)        # == fwhm(z) / sqrt(2 * ln(2))
 
     kk = 2 * pi / wl
-    Rz = zz * (1 + zr2 / z2)
+    inv_Rz = numpy.divide(zz, z2 + zr2, out=numpy.zeros_like(zz), where=(z2 + zr2) != 0)
     gouy = numpy.arctan(zz / zr)
 
-    gaussian = w0 / wz * numpy.exp(-r2 / wz2) * numpy.exp(1j * (kk * zz + kk * r2 / 2 / Rz - gouy))
+    gaussian = w0 / wz * numpy.exp(-r2 / wz2) * numpy.exp(1j * (kk * zz + kk * r2 * inv_Rz / 2 - gouy))
 
     row = gaussian[:, :, gaussian.shape[2] // 2]
-    norm = numpy.sqrt((row * row.conj()).sum())
+    norm = numpy.linalg.norm(row)
     return gaussian / norm