Grating chip for a magneto-optical trap and fabrication method

A grating chip 200 for a magneto-optical trap (GMOT) comprising four diffraction gratings 202, 204, 206, 208 (QUAD-grating), wherein each of the diffraction gratings 202, 204, 206, 208 comprises an array of grooves 210 on a surface 212 for diffracting light. The diffraction gratings 202, 204, 206, 208 diffract an input light beam 214 e.g. laser into first order diffracted beams 216 that intersect at region 218. At least one of the diffraction gratings 202, 204, 206, 208 comprises a reflective coating 211 e.g. aluminium, palladium, platinum. The grating pattern may be etched into a substrate using plasma etching. The period of the arrays of grooves may be within between 900nm to 1250nm e.g. 1080nm. The input light beam may have a wavelength of 569nm, 671nm, 767nm, 780nm or 852nm. The region 218 may be located above a point 220 at which each of the diffraction gratings 202, 204, 206, 208 touch.