EEEL Researchers Develop Novel Attenuator for High-energy Lasers

A laser attenuator having a well-known and stable attenuation can extend the usefulness of an optical power meter for laser radiometry. The challenge of building attenuators for high-power laser measurements (kW/cm² and greater) is to minimize damage and instability from heating. EEEL Researchers John Lehman, David Livigni, Xiaoyu Li, Chris Cromer, and Marla Dowell have designed a laser attenuator based on multiple partial reflections of a collimated beam at a 45° angle of incidence on an assembly of fixed, coated mirrors. The mirrors are arranged with respect to the incoming radiation such that the input and output beams are collinear and the incoming polarization is unaltered. By selecting pairs of uncoated silicon carbide, molybdenum, and copper mirrors the researchers were able to achieve an overall attenuation factor of approximately 74 with a damage threshold exceeding 250 mJ per pulse. With an accurate value of the overall attenuation, the attenuator can be used to extend the dynamic range of a calibrated laser power meter with only a small additional uncertainty. In the future, by choosing other types of mirror pairs, we can increase or decrease the attenuation factor. The attenuator has the advantage over traditional attenuator techniques because of thermal stability, polarization insensitivity, and minimal back reflection.

J. H. Lehman, D. J. Livigni, X. Li, C. L. Cromer, M. L. Dowell, "Reflective attenuator for high energy laser measurements," Applied Optics, Vol. 47, No. 18, pp. 3360-3363, (20-Jun-2008).