Using an interferometer to characterize the spatial information of a continuous-wave (CW) laser beam can be done straightforwardly using a shearing interferometer, where the test wavefront is interfered with a positionally shifted duplicate of itself. However, measuring ultrafast laser pulses using this method is more difficult, because, given the short duration of a femtosecond pulse, traditional interferometers lose their functionality.
"A simple interferometer like the shear plate, where the beams reflected from the front and back surfaces interfere, no longer works," says, Chunlei Guo, a professor of optics at the University of Rochester (Rochester, NY).
Now, Guo and his associate, Billy Lam, have come up with a simple shearing-interferometer setup that works well with ultrafast pulses of sub-100-fs duration.1 In fact, the setup can characterize amplitude, phase, polarization, wavelength, and duration of the pulse.
The interferometer contains a single beamsplitter cube with one wedged entrance face, producing an almost zero path-length difference between unsheared and sheared beams, and a very stable interference pattern.
Source: http://www.rochester.edu/newscenter/interferometer-optics-measuring-light-beam-328182/
REFERENCE:
1. Billy Lam and Chunlei Guo, Nature Light: Science and Applications (2018); https://doi.org/10.1038/s41377-018-0022-0
