Since the aluminisation in May 2002 the M1 and M2 mirrors have been C02 cleaned nine times. The last cleaning was in March and the reflectivity of M1 after CO2 cleaning was 3.5% less than just after aluminisation. The mirror cleaning procedures were studied, and a draft document was written on the current procedures and plans for the future. A ``wet'' cleaning of the mirrors is planned for May the 25th.
To help with monitoring the reflectivity, and agreement was made with the optical engineer of the ING to measure the reflectivity and the scatter of the mirrors on regular (6 weeks) intervals. This will also provided a valuable cross calibration of our own reflectometer.