{"id":328182,"date":"2018-07-11T11:34:10","date_gmt":"2018-07-11T15:34:10","guid":{"rendered":"http:\/\/www.rochester.edu\/newscenter\/?p=328182"},"modified":"2019-11-13T12:28:04","modified_gmt":"2019-11-13T17:28:04","slug":"interferometer-optics-measuring-light-beam-328182","status":"publish","type":"post","link":"https:\/\/www.rochester.edu\/newscenter\/interferometer-optics-measuring-light-beam-328182\/","title":{"rendered":"Measuring each point of a beam of light"},"content":{"rendered":"

If you want to get the greatest benefit from a beam of light\u2014whether to detect a distant planet or to remedy an aberration in the human eye\u2014you need to be able to measure it.<\/p>\n

Now a University of Rochester research team has devised a much simpler way to measure beams of light\u2014even powerful, superfast pulsed laser beams that require very complicated devices to characterize their properties.<\/p>\n

\"two
A new device designed by optics professor Chunlei Guo and PhD student Billy Lam is a \u201crevolutionary step forward\u201d for characterizing the properties of laser beams in a much more reliable and powerful way that traditional interfermoter. (University of Rochester photo \/ J. Adam Fenster)<\/figcaption><\/figure>\n

The new device will give scientists an unprecedented ability to fine tune even the quickest pulses of light for a host of applications, says Chunlei Guo, professor of optics, who has used femtosecond pulsed laser beams to treat metal surfaces in remarkable ways,<\/a> and it could render traditional instruments for measuring light beams obsolete.<\/p>\n

\u201cThis is a revolutionary step forward,\u201d says Guo. \u201cIn the past we\u2019ve had to characterize light beams with very complicated, cumbersome interferometric devices, but now we can do it with just one optical cube. It is super compact, super reliable, and super robust.\u201d<\/p>\n

The device, developed by Guo and Billy Lam, a PhD student in his lab, is described in Nature Light: Science and Applications<\/em><\/a>. Called a wedged reversal shearing interferometer, it consists of a prism cube, assembled from two right-angle prisms. The cube has two angled entrances and splits the beam into two parts.<\/p>\n

When the beam exits the cube, the reflected light from the left portion of the beam and the transmitted light from the right portion of the beam are emitted from one face of the cube. Conversely, the transmitted light from the left portion of the beam and reflected light from the right portion are emitted from another face of the cube.<\/p>\n

 <\/p>\n

\"two
At left is the basic design of a traditional interferometer, and at right the more compact design of the interferometer created in the lab of optics professor Chunlei Guo. This new wedge reversal shearing interferometer has the added advantage of being able to measure the beam front information or wave front of powerful, superfast pulsed laser beams, (University of Rochester illustration \/ Michael Osadciw)<\/figcaption><\/figure>\n

This creates an extremely stable \u201cinterference\u201d pattern for Guo and his team to measure all the key spatial characteristics of a light beam\u2014its amplitude, phase, polarization, wavelength, and\u2014in the case of pulsed beams\u2014the duration of the pulses. And not just as an average along the entire beam, but at each point of the beam of light.<\/p>\n

This is especially important in imaging applications, Guo says. \u201cIf a beam is not perfect, and there is a defect on the image, it\u2019s important to know the defect is because of the beam, and not because of a variation in the object you are imaging,\u201d Guo says.<\/p>\n

\u201cIdeally, you should have a perfect beam to do imaging. And if you don\u2019t, you better know it, and then you can correct your measurements. Ultrafast lasers are key for recording dynamic processes, and having an extremely simple but robust device to characterize ultrafast or any type of laser beams are surely important.\u201d<\/p>\n

 <\/p>\n

Characterizing laser pulses at a\u00a0millionth of a billionth of a second<\/strong><\/h3>\n

Albert Michaelson demonstrated the first interferometer in the 1880s, using a beam splitter and two mirrors. The core principles remain the same in interferometers used today.<\/p>\n

The beam splitter sends the split light on different optical paths towards the mirrors. The mirrors then reflect each split beam back so they recombine at the beam splitter. \u00a0The different paths taken by the two split beams causes a phase difference which creates an interference fringe pattern. This pattern is then analyzed by a detector to evaluate the wave characteristics.<\/p>\n

This approach has worked reasonably well for characterizing continuous wave laser beams because they have a long \u201ccoherence\u201d time, allowing them to interfere even after being split, sent along two paths of different lengths, and then recombined, Guo says.<\/p>\n