Dr. Bernhard Lau Profile

Dr. Bernhard Lau

Retired

SPIE Involvement:

Author

Publications (9)

Proceedings Article | 21 September 1999 Paper

ESPI with holographically stored waves and other innovative ESPI methods used for real-time monitoring of dynamic thermal deformations in a practical industrial environment

Valery Petrov, Bernhard Lau

Proceedings Volume 3824, (1999) https://doi.org/10.1117/12.364277

KEYWORDS: Holographic optical elements, Holography, Cameras, Optical components, Scattering, Speckle pattern, Sensors, Laser scattering, Refraction, Semiconductor lasers

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Electronic speckle pattern interferometry (ESPI) is a rapidly developing optoelectronic method of nondestructive laser metrology supported with computer evaluations. It permits measurement of deformations in the micrometer and submicrometer ranges produced by an electrical signal, heating, mechanical stress or another load. Though the method seems very friendly for industrial checks it has several drawbacks which prevent its application in real industrial environment: complexity, bulkiness and high costs of optical setups, difficulties in aligning of the optical elements. There are problems in working outside the laboratory especially due to high sensitivity of ESPI devices against environmental vibrations and daylight. The method of ESPI with holographically stored waves was introduced by these authors in 1995. It permitted to avoid all drawbacks mentioned above and to build an elegant, portable ESPI device with 2 optical components only: a HOE and a plane mirror. The device works very well with different test specimens subjected to deformations and vibrations. It was found that the method and the device also suit well for quasi-real time monitoring of dynamic thermal deformations. Such a novel possibility of ESPI to monitor temporal development of deformations due to electrical heating of electronic components populating a printed circuit board (PCB) and to locate a component subjected to excessive heating is presented in this work for the first time. Temporal development of deformations of the same PCB were monitored in quasi-real time in other innovative ESPI devices also originating from our laboratory. These portable, compact devices utilize alternative physical principles for combining of object and reference ESPI waves and guiding them to the sensor of the CCD camera. Such novel devices also ensure proper acquisition and documentation of temporal development of deformations and dynamics of propagation of thermal waves. Vast experimental data properly illustrating the possibilities of the novel methods are presented.

Proceedings Article | 27 April 1999 Paper

Compact and simple ESPI devices for testing of materials and components in microelectronic manufacturing

Valery Petrov, Robert Denker, Bernhard Lau

Proceedings Volume 3743, (1999) https://doi.org/10.1117/12.346912

KEYWORDS: Cameras, Holographic optical elements, Speckle pattern, Sensors, Optical components, Holography, Scattering, Microelectronics, Objectives, Diffusers

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With the increasing packaging density of electronic components in the integrated circuits (IC) as well as on the printed circuit boards the problems with heat dissipation also increase. Electronic speckle pattern interferometry (ESPI) is a rapidly developing optoelectronic method of nondestructive laser metrology supported with computer evaluations. It permits measurements of deformations in the micrometer and submicrometer ranges produced by an electrical signal, heating, mechanical stress or another load. Though these method seems very friendly for testing microelectronic components, composite materials, miniature devices, circuit boards, wafers etc., it has several drawbacks which prevent its application in real industrial environment: complexity, bulkiness and high costs of optical setups, difficulties in aligning of the optical elements. There are problems in working outside the laboratory especially due to high sensitivity of ESPI devices against environmental vibrations and daylight. We present several methods ESPI based on which a family of devices was built. Their unique properties permit to avoid all drawbacks mentioned above. These devices are extremely simple and compact. They are easily aligned and operated even by persons who are not skilled in optics. These devices are ideally suited for working outside the laboratory even by persons who are not skilled in optics. These devices are ideally suited for working outside the laboratory for example in a well-lit industrial environment. The innovative devices permit to measure deformations both in the plane of the object surface and perpendicular to it. A detailed description of the methods and devices given. Multiple examples of ESPI computer evaluations obtained in the novel devices with different small objects under test are presented. However these devices permit to work with much bigger objects if required. Our methods and devices are also suited for qualitative as well as quantitative analysis.

SPIE Journal Paper | 1 August 1998

Electronic speckle pattern interferometry with thin beam illumination of miniature reflection and transmission "speckling" elements for in-plane deformation measurements

Valery Petrov, Bernhard Lau

OE, Vol. 37, Issue 08, (August 1998) https://doi.org/10.1117/12.10.1117/1.602008

KEYWORDS: Holographic optical elements, Speckle pattern, Interferometry, Holography, Diffusers, Reflection, Nd:YAG lasers, Holograms, Optical components, Fringe analysis

Proceedings Article | 10 March 1998 Paper

Family of novel compact and very simple electronic speckle pattern interferometers for out-of-plane and in-plane deformation measurements

Bernhard Lau, Valery Petrov

Proceedings Volume 3348, (1998) https://doi.org/10.1117/12.302481

KEYWORDS: Holographic optical elements, Diffusers, Holography, Speckle pattern, Interferometers, Semiconductor lasers, Holograms, CCD cameras, Mirrors, Reflection

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Proceedings Article | 11 December 1996 Paper

Novel opthalmoscope incorporating a double axicon

Bernhard Lau, Volker Bartel

Proceedings Volume 2927, (1996) https://doi.org/10.1117/12.260654

KEYWORDS: Axicons, Eye, Mirrors, Light sources, Beam shaping, Imaging systems, Cones, Lamps, Cornea, Geometrical optics

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Ophthalmoscopes are used for eye fundus observation in medical diagnostics. The fundus is illuminated through the eye pupil and imaged to infinity by the patient's cornea and lens which act as a magnifier and allow direct observation by the physician's eye. In currently available ophthalmoscopes the requirement of simultaneously illuminating and observing the fundus is met by tilting the optical axis of the illumination ray path with respect to the observation ray path to separate them. This also reduces the blinding effect of reflections from the patient's cornea. However by this tilt the illuminated and observed fields of the fundus no longer coincide which strongly reduces the usable field of view especially when the patient's eye pupil has a small diameter. Hence in most cases the pupil is dilated for such diagnostic check-up, which on the other hand is time consuming and very discomforting for the patient. We avoid this drawback by using coaxial ray paths for illumination and observation. To separate them the illumination beam is expanded to a hollow- cone shape by a double axicon. The illumination beam is guided into the patient's eye by means of a 90 degree deflecting mirror. For fundus observation a hole is drilled in the mirror within the dark center of the expanded illumination beam. This illumination system allows application of Kohler's illumination principle, i.e. the light source can be imaged onto the patient's eye pupil which reduces influence of the latter on the extent of the illuminated area. This illumination principle cannot be applied in conventional ophthalmoscopes. For practical application an ophthalmoscope with this novel illumination system offers the following advantages: (1) field of view is completely illuminated, (2) pupil dilation is not necessary, (3) corneal reflections do not affect fundus observation, (4) illumination light losses are reduced to minimum, (5) handling of such an ophthalmoscope is very convenient and easy to learn, (6) ophthalmoscopy can be performed in emergency situations under severe time restrictions. These advantages may enable ophthalmoscopic investigations in much wider fields compared to currently used illumination principles.

Proceedings Article | 18 September 1996 Paper

Holographic data acquisition and display in real and quasi-real time: friendly for industrial inspections

Valery Petrov, Bernhard Lau

Proceedings Volume 2782, (1996) https://doi.org/10.1117/12.250759

KEYWORDS: Holography, Holograms, Data acquisition, Inspection, Silver, Optical inspection, Laser optics, Laser applications, Optoelectronics, Data processing

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Proceedings Article | 18 September 1996 Paper

Bridging the gap between electronic speckle pattern interferometry and holography

Bernhard Lau, Valery Petrov

Proceedings Volume 2782, (1996) https://doi.org/10.1117/12.250760

KEYWORDS: Holography, Speckle pattern, Holographic optical elements, Interferometry, Nondestructive evaluation, Holographic interferometry, Optical inspection, CCD cameras, Interferometers, Optical components

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Proceedings Article | 23 August 1996 Paper

Application of combined method of electronic speckle pattern interferometry and holography to vibration analysis

Bernhard Lau, Peter Kuschnir, Uwe Schmid, Valery Petrov

Proceedings Volume 2868, (1996) https://doi.org/10.1117/12.248657

KEYWORDS: Holography, Speckle pattern, Holographic optical elements, Interferometry, Vibrometry, Holographic interferometry, Semiconductor lasers, Speckle, Cameras, CCD cameras

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SPIE Journal Paper | 1 August 1996

Electronic speckle pattern interferometry with a holographically generated reference wave

Valery Petrov, Bernhard Lau

OE, Vol. 35, Issue 08, (August 1996) https://doi.org/10.1117/12.10.1117/1.600788

KEYWORDS: Holographic optical elements, Holography, Speckle pattern, Holograms, Interferometry, Cameras, Mirrors, Semiconductor lasers, Holographic interferometry, Optical components

Showing 5 of 9 publications

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