A system for monitoring a building structure is described. The system comprises a laser source which emits an infrared radiation and an interferometric arrangement which divides the radiation into an object beam and a reference beam. The object beam irradiates the building structure and is scattered by it, while the reference beam interferes with the scattered object beam so as to create a hologram of the building. The system also comprises a sensor which detects a sequence of holograms and a processing unit which reconstructs the evolution in time of deformations or displacements of the building by numerically processing the sequence of holograms. The system—being based on digital holography—offers various advantages compared to known monitoring techniques, for example techniques which make use of seismometers (possibility of remote monitoring, substantial space-time continuity of the monitoring, capacity for detecting a wider range of deformations and displacements).

A measurement device, for measuring the shape of an interface to be measured of an optical element having a plurality of interfaces, the device including: measurement apparatus with at least one interferometric sensor illuminated by a low-coherence source, for directing a measurement beam towards the optical element to pass through the plurality of interfaces, and to detect an interference signal resulting from interferences between the measured measurement beam reflected by the interface and a reference beam; positioning apparatus configured for relative positioning of a coherence area of the interferometric sensor at the level of the interface to be measured; digital processor for producing, based on the interference signal, an item of shape information of the interface to be measured according to a field of view.

A measurement method, for measuring the shape of an interface of an optical element having a plurality of interfaces is also provided.

The present invention provides a surface shape measuring device and a surface shape measuring method which do not require a physical reference plane and can improve measurement accuracy without using a mechanical adjustment mechanism. The illumination light condensing point P.sub.Q and the reference light condensing point P.sub.L are arranged as mirror images of each other with respect to the virtual plane VP, and each data of the object light O, being a reflected light of the spherical wave illumination light Q, and the inline spherical wave reference light L is recorded on each hologram. On the virtual plane VP, the reconstructed object light hologram h.sup.V for measurement is generated, and the spherical wave optical hologram s.sup.V representing a spherical wave light emitted from the reference light condensing point P.sub.L is analytically generated. The height distribution of the surface to be measured of the object 4 is obtained from the phase distribution obtained by dividing the reconstructed object light hologram h.sup.V by the spherical wave light hologram s.sup.V. High-accuracy surface shape measurement without requiring a reference plane such as a glass substrate is realized by comparing the phase data of the reflected light acquired from the surface to be measured and the phase distribution on the plane cut surface of the spherical wave obtained analytically.

The invention relates to a free-beam interferometric method for illuminating a sequence of sectional areas in the interior of the light-scattering object. The method makes it possible for the user to select a larger image field and/or a higher image resolution than previously possible with the occurrence of self-interference of the specimen light from a scattering specimen.

The illumination light condensing point P.sub.Q and the reference light condensing point P.sub.L are arranged as mirror images of each other with respect to the virtual plane VP, and each data of the object light O, being a reflected light of the spherical wave illumination light Q, and the inline spherical wave reference light L is recorded on each hologram. On the virtual plane VP, the reconstructed object light hologram h.sup.V for measurement is generated, and the spherical wave optical hologram s.sup.V representing a spherical wave light emitted from the reference light condensing point P.sub.L is analytically generated. The height distribution of the surface to be measured of the object 4 is obtained from the phase distribution obtained by dividing the reconstructed object light hologram h.sup.V by the spherical wave light hologram s.sup.V.

A metrology system including a heterodyne light source is provided. The heterodyne light source includes a first light source, an acousto-optic modulator and a source optical arrangement. The acousto-optic modulator receives at least one wavelength laser beam from the first light source and generates at least one corresponding frequency shifted laser beam (e.g., with orthogonal polarization). The source optical arrangement includes a receiving optical element portion and a birefringent optical element portion. The receiving optical element portion receives the wavelength laser beam(s) and the corresponding frequency shifted laser beam(s) and directs the beams along an optical path toward the birefringent optical element portion. The birefringent optical element portion combines the beams to output a combined beam (e.g., which may be utilized as part of a measurement process to determine at least one measurement distance to at least one surface point on a workpiece, etc.).

A method for measuring the surface topography of an object including the following steps: a) providing source radiation and dividing the source radiation into illumination radiation and reference radiation, b) illuminating the surface of the object with illumination radiation in a planar illumination field, the surface of the object being illuminated simultaneously with more than one spatial radiation mode and the radiation modes of the illumination being spatially and temporally coherent, but with a fixed phase difference from one another, and c) overlaying the reference radiation on illumination radiation back-scattered at the surface of the object, and detecting an interference signal of the overlaid radiation with a detector. Steps a) to c) are carried out for at least two different, fixed wavelengths. The surface topography of the object is determined by means of digital holography.

Various optical systems equipped with diode laser light sources are discussed in the present application. One example system includes a diode laser light source for providing a beam of radiation. The diode laser has a spectral output bandwidth when driven under equilibrium conditions. The system further includes a driver circuit to apply a pulse of drive current to the diode laser. The pulse causes a variation in the output wavelength of the diode laser during the pulse such that the spectral output bandwidth is at least two times larger than the spectral output bandwidth under the equilibrium conditions.

Apparatus for detecting a 3D structure of an object, comprising at least three laser emitters and a beam splitter that splits the laser radiation of the laser emitters into a reference radiation and an illumination radiation. The illumination radiation strikes the object to be measured, is reflected by the object as object radiation and interferes with the reference radiation. A detector receives the interference patterns formed from the interference of the reference and object radiation and an analysis unit analyzes the interference patterns. At least two of the laser emitters emit laser radiation in the invisible range and the analysis unit detects the object in three dimensions based on the interference patterns of the invisible laser radiation. At least one of the laser emitters emits colored laser radiation and the analysis unit deduces the object's color based on the intensity of the colored object radiation reflected by the object.

Methods, systems and computer program products for performing visual quality assessment using holographic interferometry are provided. Aspects include obtaining a reference holographic pattern based on a reference object and obtaining a test holographic pattern based on a test object. Aspects also include creating an interference pattern by superimposing the test holographic pattern onto the reference holographic pattern. Aspects further include determining a difference between the reference object and the test object based upon the interference pattern.