193nm excimer laser radiation needs special precautions in measurement because of its strong interaction with ordinary matter. This radiation is absorbed by ordinary air and water vapor in the air so that the intensity measured can vary by 1% per cm. Therefore, for accurate measurements, make sure the distance from the laser to the measurement device is the same as the distance to the point at which you wish to know the power/energy. Furthermore, when using an energy sensor with a diffuser, note that the diffuser surface can adsorb gas and water vapor when left for some days without use and this can lower the reading by several percent. Run the laser on the sensor for up to one minute or until the reading stabilizes, and then take the measurement.