Optical Measurement Section, NRLM, AIST
Femtosecond Technology
- Dimensional measurement using chirped pulse
The time delay was converted to difference of color using chirped light
pulse, then selected by an optical shutter gated femtosecond pulse and three
dimensional shape was measured at a shot. To get higher longitudinal resolution,
the response time of optical Kerr shutter was improved. The measurement
were performed not only for objects of mirror surface but also for transparent
or diffusing objects.
Principle of the measurement
Step Measurement using three gauge blocks
- Measurements of complex optical system
A novel method to measure dimensions of complicated optical system was developed,
combining conventional interferometry and temporal discrimination among
lights reflected by multiple interface using pulses. An optical center of
a corner cube prism of 60 mm optical path was determined with resolution
of 1.5 mm. Position of the interface of 2 liquid layers was also determined,
although the reflectivity at the interfaces was very small, about 0.3 %.
Furthermore, femtosecond two-color interferometry (FTI) using pulse laser and its SHG was
developed to measure shape and thickness of a lens using the same optical configuration. The technique is utilizing temporal localization and high peak power of the femtosecond optical pulses. The FTI derives good stability in measurement due to the near-common path and easy alignment even though the coherence of the laser is low. The FTI could even be used for in-situ dimensional measurement of complex optical parts with low reflective surfaces and rather tight curvatures.
Principle of the measurement
