diff --git a/lasy/optical_elements/__init__.py b/lasy/optical_elements/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/lasy/optical_elements/optical_element.py b/lasy/optical_elements/optical_element.py
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+++ b/lasy/optical_elements/optical_element.py
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+
+class OpticalElement(object):
+    """
+    Base class to model thin optical elements.
+
+    Any optical element should inherit from this class, and define its own
+    `amplitude_multiplier` method, using the same signature as the method below.
+    """
+
+    def __init__(self):
+        pass
+
+    def amplitude_multiplier(self, x, y, omega):
+        """
+        Return the complex number :math:`T` with which to multiply the
+        complex amplitude of the laser just before this thin element,
+        in order to obtain the complex amplitude output laser just
+        after this thin element:
+
+        .. math::
+
+            \tilde{\mathcal{E}}_{out}(x, y, \omega) = T(x, y, \omega)\tilde{\mathcal{E}}_{in}(x, y, \omega)
+
+        Parameters
+        ----------
+        x, y, omega: ndarrays of floats
+            Define points on which to evaluate the multiplier.
+            These arrays need to all have the same shape.
+
+        Returns
+        -------
+        multiplier: ndarray of complex numbers
+            Contains the value of the multiplier at the specified points
+            This array has the same shape as the arrays x, y, omega
+        """
+        # The base class only defines dummy multiplier
+        # (This should be replaced by any class that inherits from this one.)
+        return np.zeros_like(x, dtype="complex128")