Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Splitting Of White Light

26.04.2004


Moscow scientists have managed to do simply and inexpensively something which normally proves complicated and expensive. The concept thought out and then implemented is a device which allows you to check the quality of ground and polished surfaces with unprecedented precision and rapidity and to detect every single defect of such surfaces. The effort has been funded by both the Russian Foundation for Basic Research and the Foundation for Promotion of Small-Size Enterprises in Research and Technical Areas.



The source of light for contemporary devices for the check of the quality of grinded surfaces are lasers, which are not cheap, but the correct interpretation of measurement results could be produced only by a specialist with extensive experience and intuition. The fact is that the interference acquired in this case does not allow to identify the type of defect – be it convexity or concavity. Now the situation can drastically change. The laser turns out to be successfully replaced by a common white light bulb, and intuition will not be needed at all. Therefore, the device will provide distinct results at the output, and there will be no need to guess what defects exist on the mirror surface.

The new device is called “digital interferometer with incoherent source”. The device was invented and manufactured by the specialists of the Moscow Physical & Engineering Institute (State University), Moscow State Engineering University STANKIN and Research-and-Production Association “Energomekhanika” with financial support of the Russian Foundation for Basic Research and the Foundation for promotion of small-size enterprises in research and technical areas. The project was headed by Nikolai Vlasov, Professor, Doctor of Technical Sciences.


“The device action is based on interference of common white light (and this is reflected in its name). The essence of the work is as follows, says Professor Vlasov. The beam of light from one source is split into two absolutely identical beams. They are called the reference one and the object one. One of them is directed at the mirror which is initially of high-quality. The other is directed at the object under consideration, the distances to the object being equal. That is also the mirror, the surface quality of which should also be checked for concavities and convexities, and measured them, if any. If the “ heights” or “hollows” are too extensive and exceed the allowable value – the mirror is culled, if the defects are nonexistent or insignificant – the mirror is permitted for work.”

However, the question arises how the defects can be measured? So, both beams are reflected, each from its mirror. Then they are joined with the help of a semitransparent mirror to see what would turn out. Each of the beams has passed its way, the difference between the ways being the deflection of the object surface height from flat surface: if the beam hits a concavitiy, the length of its way increases, if it hits a convexity – its way decreases by the height of the convexity.

If the difference is divisible by the length of the light length, it intensifies – this phenomenon is called interference. If not – one beam extinguishes the other. The so-called fringe pattern is obtained – i.e. light and dark bands. Their number equals the number of times the light wave-length “goes into” the difference of ways. As the light source is normally the laser beam of a certain wave-length, this distance can be easily calculated. Nevertheless – and this is very important – the position of the bands would not help to determine whether the way passed by the beam reflected from the objects was longer or shorter. That is, if the mirror is convex or, on the contrary, concave.

For this purpose, the operates has to rely upon his/her experience and intuition. For example, when polishing the mirror, the pressure is higher at the middle of it – that means that the “relief drop” can be expected in that area. The sides of the mirror experience lower pressure - that means that convexities can be found there. That cannot be expressed in numbers.

That particular task can be fulfilled by a new device. If the lengths of the ways gone by light are absolutely identical, then regardless of the its wave-length, interference occurs upon overlapping of identical beams – since the difference of legths turns out to equal zero. The interferogram shows bright contrast band surrounded by the so-called black fringe – it is called the zero order band. That means that the only thing to be done is to make the two ways of two beams equal. To this end, it is sufficient to slightly shift the “correct” flat sample mirror at a certain distance in the known direction – either closer or farther away. That is performed by a special mechanism.

So, the method is as follows: the light goes in two beams, the fringe pattern is recorded – i.e. it is photographed, digitized and the zero order interference band is input in the computer memory. Then the mirror is relocated by one step and the procedure is repeated. The mirror is shifted to and fro. Several step-by-step images are acquired – i.e. a series of interference bands is obtained, processed and summed up. As a result, the answer if obtained in numbers whether the way length of the beam reflected from the sample mirror is longer or shorter that that of its twin reflected from the mirror that is the object of investigation. Therefore, the mirror quality has been checked. This method is very simple and precise.

“Certainly, our method is not deprived of drawbacks, says Nikolai Vlasov. For example, it cannot compete with the laser one if a nonstationary object needs to be investigated – we require some time. However, our method has no equal for an enormous number of common measurements and polishing quality control.”

Sergey Komarov | alfa
Further information:
http://www.informnauka.ru

More articles from Process Engineering:

nachricht Quick, Precise, but not Cold
17.05.2017 | Fraunhofer-Institut für Lasertechnik ILT

nachricht A laser for divers
03.05.2017 | Laser Zentrum Hannover e.V.

All articles from Process Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

Gold shines through properties of nano biosensors

17.08.2017 | Physics and Astronomy

Greenland ice flow likely to speed up: New data assert glaciers move over sediment, which gets more slippery as it gets wetter

17.08.2017 | Earth Sciences

Mars 2020 mission to use smart methods to seek signs of past life

17.08.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>