An optical metrology device produces light in a spectral range for measurement of a sample using a tunable Quantum Cascade Laser (QCL). The optical metrology device includes a second channel that is used to diagnose when the tunable QCL is in failure mode, e.g., when it is not producing all wavelengths in the plurality of different wavelength ranges. The second channel includes at least one optical flat that is transmissive to the light produced by the QCL and is separate from the tunable QCL. The optical flat is switchably placed in a beam path of the light produced by the tunable QCL and light transmitted through the optical flat is received by a detector. Using output signals from the detector, a failure mode of the tunable QCL may be determined.

An electro-optical system has a laser drive electronic circuit, a laser light source and an optical interferometer, forming a closed loop. The laser drive electronic circuit is arranged to receive a reference frequency as input, and a beat frequency as feedback. The laser drive electronic circuit generates a drive output based on a phase difference between the reference frequency and the beat frequency. The optical interferometer, coupled to the laser light, generates optical energy at the beat frequency.

Apparatus, methods and systems relating to fluorescence imaging, and more particularly, to reducing or eliminating light sensitive and insensitive background noise in fluorescence spectroscopy systems, as well as optical coherence tomography (OCT) systems.

Some embodiments of the invention relate to a laser tracker for progressive tracking of a reflective target and for determining the distance to the target having a distance measuring unit, which is designed as an interferometer, for determining a distance change to the target by means of interferometry, a laser beam source for generating measuring radiation for the interferometer, a base, which defines a standing axis, a beam guiding unit for emitting the measuring radiation and for receiving at least a part of the measuring radiation reflected on the target, wherein the beam guiding unit is pivotable by a motor about the standing axis and an inclination axis, which is essentially orthogonal in relation to the standing axis, in relation to the base, and an angle measuring functionality for determining an alignment of the beam guiding unit in relation to the base.

Disclosed is a method for measuring etch depth including the following steps: splitting a light beam into a first, and respectively second, incident beam directed towards a first, respectively second, area of a sample exposed to an etching treatment to form a first, and respectively second, reflected beam, recombining the first reflected beam and the second reflected beam to form an interferometric beam; detecting a first, and respectively second, interferometric intensity signal relative to a first, respectively second, polarisation component; calculating a lower envelope function and an upper envelope function of a differential polarimetric interferometry signal; determining an offset function and a normalisation function from the first lower envelope function and the first upper envelope function; and calculating a differential polarimetric interferometry function normalised locally at each time instant.

A method of measuring a particle density of particles includes emitting, by a laser, a laser beam directed to a mirror, redirecting the laser beam by the mirror with a predetermined periodic movement, and focusing the laser beam to a detection volume by an optical imaging device. The method further includes determining a self mixing interference signal of an optical wave within a laser cavity if the self mixing interference signal is generated by laser light of the laser beam reflected by at least one of the particles and suppressing a false self mixing interference signal for particle detection if the self mixing interference signal is caused by a disturbance in an optical path of the laser beam. The false self mixing signal caused by the disturbance in the optical path of the laser beam is suppressed in a defined range of angles of the mirror during the periodic movement.

Techniques for removing interferometry signal phase variations caused by distortion and other effects in a multi-layer stack include: providing an electronic processor sample interferometry data acquired for the stack using a low coherence imaging interferometry system; transforming, by the electronic processor, the sample interferometry data to a frequency domain; identifying a non-linear phase variation from the sample interferometry data in the frequency domain, in which the non-linear phase variation is a result of dispersion introduced into a measurement beam by the test sample; and removing the non-linear phase variation from the sample interferometry data thereby producing compensated interferometry data.

The methods disclosed herein include recording at near-vertical first and second measurement positions respective first and second interferograms of the photomask surface and defining a difference map as the difference between the first and second interferograms. Respective first and second normal forces on the photomask are also measured at the first and second measurement positions. The change in the normal force is used define a scaling factor, which is applied to the difference map to define a scaled difference map. A compensated flatness measurement with a reduced shape contribution due to gravity is obtained by subtracting the scaled difference map from the first interferogram. An interferometer-based flatness measurement system is also disclosed.

Length metrology apparatuses and methods are disclosed for measuring both specular and non-specular surfaces with high accuracy and precision, and with suppressed phase induced distance errors. In one embodiment, a system includes a laser source exhibiting a first and second laser outputs with optical frequencies that are modulated linearly over large frequency ranges. The system further includes calibration and signal processing portions configured to determine a calibrated distance to at least one sample.

An electro-optical system has a laser drive electronic circuit, a laser light source and an optical interferometer, forming a closed loop. The laser drive electronic circuit is arranged to receive a reference frequency as input, and a beat frequency as feedback. The laser drive electronic circuit generates a drive output based on a phase difference between the reference frequency and the beat frequency. The optical interferometer, coupled to the laser light, generates optical energy at the beat frequency.