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 Jelly with memory – predicting the leveling of com-mercial paints
15.12.2017 | Fraunhofer-Institut für Produktionstechnik und Automatisierung IPA

nachricht Fraunhofer researchers develop measuring system for ZF factory in Saarbrücken
21.11.2017 | Fraunhofer-Institut für Zerstörungsfreie Prüfverfahren IZFP

All articles from Process Engineering >>>

The most recent press releases about innovation >>>

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

Im Focus: First-of-its-kind chemical oscillator offers new level of molecular control

DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.

Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Diamond Lenses and Space Lasers at Photonics West

15.12.2017 | Trade Fair News

A better way to weigh millions of solitary stars

15.12.2017 | Physics and Astronomy

New epidemic management system combats monkeypox outbreak in Nigeria

15.12.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>