Jazyky

Laboratoř interferometrie

Jedním z pracovníků skupiny klasické optiky je Pavel Pavlíček. Zabývá se výzkumem v oblastech: interferometrie v bílém světle, profilometrie s prostorovou koherencí a interferometrie se dvěma vlnovými délkami.

Interferometrie v bílém světle

ilustrační fotografieInterferometrie v bílém světle je ověřená metoda pro měření 3D topografie technických drsných povrchů a hladkých (odrazných) povrchů s vysokou (u drsných povrchů s mikrometrovou a u hladkých s nanometrovou) přesností. V této metodě se obvykle používá Michelsonův interferometr, jehož zdroj světla má široké spektrum (bílé světlo). Princip měření spočívá v hloubkovém skenování během nějž je měřený předmět posouván v podélném směru. Tímto způsobem se mění rozdíl optických drah mezi předmětovým a referenčním svazkem v přesně definovaném rozsahu. Na výstupu interferometru je umístěna maticová kamera jako mnohonásobný detektor. Intenzita světla zaznamenaná pro různé polohy měřeného předmětu tvoří interferogram. Z poloh interferogramů zaznamenaných všemi pixely kamery je možné sestavit 3D topografickou mapu měřeného předmětu. SOUVISEJÍCÍ PUBLIKACE

Profilometrie s prostorovou koherencí

ilustrační fotografieProfilometrie s prostorovou koherencí je metoda pro měření geometrického tvaru předmětu. Nejdůležitější částí měřicí sestavy je Michelsonův interferometr osvětlený monochromatickým plošným zdrojem světla. Vlivem prostorové koherence se na výstupu interferometru objeví korelogram, který je možné použít pro měření geometrického tvaru předmětu. Tento korelogram tvoří analogii korelogram známého z interferometrie v bílém světle, který je způsoben časovou koherencí. SOUVISEJÍCÍ PUBLIKACE

Interferometrie se dvěma vlnovými délkami

ilustrační fotografieJednou z nevýhod interferometrie v bílém světle je, že zdroje se širokým spektrem mají nízký jas. Obejít tuto nevýhodu je možné tím, že se zdroj se širokým spektrem nahradí dvěma lasery s různými vlnovými délkami. Při měření tvaru je měřený předmět posouván podél optické osy a přitom je na výstupu interferometru zaznamenáván interferogram, který má typický tvar záznějového obrazce. Vyhodnocením takového interferogramu je možné určit podélnou souřadnici povrchu předmětu a tak změřit jeho geometrický tvar. Díky vysokému jasu laserů je možné měřit i tvar předmětů se slabě odrážejícím povrchem. Vhodným výběrem dvou nebo více laserů je možné tvarovat koherenční funkci podle požadavků měřicí úlohy. SOUVISEJÍCÍ PUBLIKACE


SOUVISEJÍCÍ PUBLIKACE

Interferometrie v bílém světle

 

papers

 

P. Pavlíček, O. Hýbl: White-light interferometry on rough surfaces - measurement uncertainty caused by surface roughnes,

Applied Optics 47, 2941-2949 (2008).

 

Abstract:

White-light interferometry measuring an optically rough surface commonly does not resolve the lateral structure of the surface. This means that there are height differences within one resolution cell that exceed one-fourth of the wavelength of the light used. Thus the following questions arise: Which height is measured by white-light interferometry? How does the surface roughness affect the measurement uncertainty? The goal of the presented paper is to answer these questions by means of numerical simulations. Before the aforementioned questions can be answered, the distribution of the intensity of individual speckles, the influence of surface roughness, and the spectral width of the light source used are discussed.

 

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P. Pavlíček, G. Häusler: White-light interferometer with dispersion: an accurate fiber-optic sensor for the measurement of distance,

Applied Optics 44, 2978-2983 (2005).

 

Abstract:

We present a fiber-optical sensor for distance measurement of smooth and rough surfaces that is based on white-light interferometry; the sensor measures the distance from the sample surface to the sensor head. Because white light is used, the measurement is absolute. The measurement uncertainty depends not on the aperture of the optical system but only on the properties of the rough surface and is commonly ~1 μm. The measurement range is approximately 1 mm. The sensor includes no mechanical moving parts; mechanical movement is replaced by the spectral decomposition of light at the interferometer output. The absence of mechanical moving parts enables a high measuring rate to be reached.

 

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P. Pavlíček: Height profile measurement by means of white light interferometry,

Proceedings of the society of photo-optical intstrumentation engineers (SPIE), volume: 5259, pages: 139-144 (2003) 13th Polish-Czech-Slovak Conference on Wave and Quantum Aspects of Contemporary Optics, September 9-13, 2002 Krzyzowa, Poland.

 

Abstract:

White light interferometry is an established method for height profile measurement of objects. This method, unlike classical interferometry, can be used for measurement of objects with rough surface, which is an important advantage.

The white light interferometer is in principle a Michelson interferometer with a broad-band light source and a CCD camera as a detector. The Michelson interferometer has the object to be measured in one arm and the reference mirror in the other arm. Due to the reflection on the rough surface, a speckle pattern arises in the detector plane. This pattern is superimposed on the reference wave. The phase in particular speckle is random, but it remains approximately constant within one speckle. This renders the white light interference observable, if the optical path lengths of the two arms differ less than the coherence length.

The object to be measured is mounted on a micropositioner for translating in the longitudinal direction. Gradually, as parts of the object surface cross the reference plane, the white light interference is observable in the corresponding speckles. The position of the micropositioner, in which the interference is maximal, is stored for each pixel. This value for each pixel of the object image describes the geometrical shape of the measured object.

The measuerement range is theoretically unlimited, practically it is limited by the range of the micropositioner. The longitudinal uncertainty does not depend on the parameters of the optical setup, its value is given by the roughness of the measured surface. The height profile of the object is measured during one measurement process, unlike the scanning profilers. The illumination and the observation are coaxial, which avoids shadows.

 

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P. Pavlíček, J. Soubusta: Measurement of the influence of dispersion on white-light interferometry,

Applied Optics 43, 766-770 (2004).

 

Abstract:

White-light interferometry is a well-established method for measuring the height profiles of samples with rough as well as with smooth surfaces. Because white-light interferometry uses broadband light sources, the problem of dispersion arises. Because the optical paths in the two interferometer arms cannot be balanced for all wavelengths, the white-light correlogram is distorted, which interferes with its evaluation. We investigate the influence of setup parameters on the shape of the correlogram. Calculated values are compared with experimental results.

 

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P. Pavlíček, J. Soubusta: Theoretical measurement uncertainty of white-light interferometry on rough surfaces,

Applied Optics 42, 1809-1813 (2003).

 

Abstract:

A great advantage of the white-light interferometry is that it can be used for profile measurement of objects with a rough surface. A speckle pattern that arises in the image plane allows one to observe the interference; however, this pattern is also the source of the measurement uncertainty. We derive the theoretical limits of the longitudinal uncertainty by virtue of the first-order statistics of the speckle pattern. It is shown that this uncertainty depends on the surface roughness of the measured object only; it does not depend on the setup parameters.

 

diploma theses:

 

Ondřej Hýbl: Měření tvaru předmětu pomocí interferometrie v bílém světle se spektrálním rozkladem (2005).

 

Profilometrie s prostorovou koherencí

 

papers:

 

P. Pavlíček, M. Takeda: Similarities and Differences between Spatial Coherence Profilometry and White-light Interferometry,

International Conference on Advanced Phase Measurement Methods in Optics and Imaging, book series AIP Conference Proceedings, volume: 1236, pages: 161-166 (2010).

 

Abstract:

Spatial coherence profilometry is a method that uses a Michelson interferometer illuminated by a quasimonochromatic spatially extended light source to measure the shape of objects. Because of the spatially extended light source, this method takes advantage of spatial coherence of the light. Thus spatial coherence profilometry appears to be a spatial coherence analogy to white-light interferometry which is a reliable and proved method for the measurement of the shape of objects. White-light interferometry usually uses a Michelson interferometer illuminated by a polychromatic point-like light source and so is based on temporal coherence. Though these both measurement methods look similar they show some significant differences. By means of theoretical analysis and experiments we investigate what is similar and where are the differences between these both methods.

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P. Pavlíček, M. Halouzka, Z. Duan, M. Takeda: Spatial coherence profilometry on tilted surfaces,

Applied optics 48, H40-H47 (2009).

 

Abstract:

The influence of tilted surfaces on the measurement of shape by spatial coherence profilometry is investigated. Based on theoretical analysis and experimental results, the systematic measurement error caused by surface tilt is determined. The systematic measurement error depends not only on the tilt angle but also on the parameters of the experimental setup. The theoretical analysis and the experiments show the similarities and differences between spatial coherence profilometry and white-light interferometry. We also suggest the conditions to obtain correct measurements by use of spatial coherence profilometry.

 

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P. Pavlíček, Z. Duan, M. Takeda: Spatial coherence profilometry,

Proceedings of the society of photo-optical intstrumentation engineers (SPIE), volume: 6609, pages: 60916-60916 (2007) 15th Czech-Polish-Slovak Conference on Wave and Quantum Aspects of Contemporary Optics, September 11-15, 2006 Liberec, Czech Republic.

 

Abstract:

Spatial coherence profilometry is a method for measurement of the geometrical form of objects. In addition to the two lateral coordinates x and y, it measures the longitudinal coordinate z. In this way the complete 3D description of the object's surface is acquired.

The main piece of the presented method is a Michelson interferometer illuminated by a monochromatic spatially extended light source. The surface of the object whose geometrical form should be measured is used as one mirror of the Michelson interferometer. By moving of the measured object along the optical axis, the intereference is observable only if the object's surface occurs in the vicinity of the so-called reference plane. The reference plane is given by the position of the object mirror when the Michelson interferometer is balanced. The described effect follows from the form of the spatial coherence function originated by the spatially extended light source.

If the intensity at the output of the interferometer is recorded as a function of the position of the measured object, a typical correlogram arises. This correlogram is similar to that known with white-light interferometry. From the maximum of the correlogram, the z coordinate of the object's surface can be determined. Usually a CCD camera is used as the detector at the output of the Michelson interferometer. Then z coordinates of many surface points are parallel measured in the course of one measurement procedure and the 3D description of the object's surface is acquired. The scanning in the lateral direction is not necessary. Thus the described method provides a spatial coherence analogy to white-light interferometry which is based on temporal coherence. Unlike to the white-light interferometry, the described method does not require a broadband light source, the interferometer is illuminated by a monochromatic light source, usually a laser.

 

diploma theses:

 

Marek Halouzka: Optical 3D sensors for shape measurement of objects (2008).

 

Marek Šimíček: Určování topologie povrchů pomocí analýzy zaostření (2007).

 

Interferometrie se dvěma vlnovými délkami

 

papers:

 

P. Pavlíček, G. Häusler: Measurement of the shape of objects by the interferometry with two wavelengths, Proceedings of The 6th International Workshop on Advanced Optical Metrology, Springer, pages 339 - 344, September 13 - 16, 2009, Nürtingen, Germany.

 

White-light interferometry is an established method for the measurement of geometrical shape of object with smooth or rough surface. One of the disadvantages of white-light interferometry is that the required broadband light sources suffer from a low luminance. This shows up when the shape of object with a weakly reflecting surface is measured or when the measured area is large. One way to overcome this disadvantage is to replace the broadband light source by two (or more) lasers with various wavelengths.

If the broadband light source is replaced by two lasers with various wavelengths, a typical beat pattern arises at the output of the interferometer instead of white-light interferogram. The beat pattern can be used for the determination of the position of the object's surface in a similar way as white-light interferogram. Unlike to white-light interferogram, the beat pattern is periodic and therefore the unambiguity range is limited.

 

diploma theses:

 

Vladimír Kocour: Měření tvaru předmětů pomocí interferometrie se dvěma vlnovými délkami (2010).

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