Laser surface profilometer with sub-Angstrom resolution

摘要

Single point diamond turning technology, has allowed the manufacture of highly aspheric optics that were unimaginable just a few years ago. Testing these optics is typically either expensive (i.e. null lens systems), destructive (contacting stylus profilers), or slow (existing optical profilers). We describe a noncontacting surface profilometer with 5 (mu)m lateral spatial resolution and sub-Angstrom height resolution. The instrument is configured as a polarizing interferometer that operates at near zero path difference and uses a visible laser diode as a light source. The instrument incorporates an autofocussing mechanism that allows high resolution profilometry over a vertical range of (plus minus)1 mm. The system bandwidth of 200 kHz allows for very fast profiling (87 cm/sec) without loss of resolution. The sensor head is very compact (6 (times) 6 (times) 10 cm) and all the processing electronics are contained on a single PC-compatible card. The instrument's autofocussing feature, high speed capability and compact size make it ideally suited for inprocess and final acceptance testing of steep aspheric optics. We will present data that demonstrates our ability to accurately measure the macroscopic and microscopic features of single point diamond turned aspheric optics typically used in high resolution X-ray lithography systems.