(a) Lambda detector spatial data showing the grating diffraction at a distance of 5 m downstream of the grating. The zeroth-order beam is blocked by a beam stop. The higher-order diffractions are spread in the horizontal direction. The vertical diffraction spots are due to support structures in the gratings. Those spots are very low in intensity with respect to the horizontal diffraction orders. (b) Intensity line profile from the Lambda detector image across the grating diffraction orders up to the fourth order.