Evangelos Papastathopoulos

Chromatic confocal spectral interferometry

Chromatic confocal spectral interferometry (CCSI) is a novel scheme for topography measurements that combines the techniques of spectral interferometry and chromatic confocal microscopy. This hybrid method allows for white-light interferometric detection with a high NA in a single-shot manner. To the best of our knowledge, CCSI is the first interferometric method that utilizes a confocally filtered and chromatically dispersed focus for detection and simultaneously allows for retrieval of the depth position of reflecting or scattering objects utilizing the phase (modulation frequency) of the interferometric signals acquired. With the chromatically dispersed focus, the depth range of the sensor is decoupled from the NA of the microscope objective.

Chromatically dispersed interferometry with wavelet analysis

A new white-light interferometry point sensor utilizing a chromatically dispersed depth detection field is addressed. Monitoring the interference in the optical frequency domain allows for microscopic height detection without the necessity of a mechanical axial scan. The problem of limited dynamic range in previously reported spectral interferometric schemes is solved by forming a high-contrast interference window due to the chromatically dispersed focusing of the detection field. In a proof-of-principle experiment, the position of a reflecting object could be retrieved with a focus of 0.8 NA over an axial range of 30 microm by analyzing the phase of the emerging interference wavelets.

Chromatic confocal spectral interferometry with wavelet analysis

In the present paper, we address a hybrid technique which combines the method of spectral interferometry with chromatic confocal microscopy. On the basis of some proof-of-principle experiments, it is shown that with this new concept, the axial detection range of the sensor is decoupled from the limited depth-of-focus of the employed microscope objective, and a high numerical aperture objective can be employed for detection. The attained interferometric signals consist of high-contrast wavelets, measured in the λ-domain. The position of an investigated object is measured by analyzing the spectral-phase of the attained wavelets. In particular, chirp-effects as well as the significant role of confocal filtering are discussed.

Chromatic Confocal Spectral Interferometry — (CCSI)

In this paper, we report on the recent development of a novel low coherence interferometry technique for the purpose of 3D-topography measurements. It combines the well established techniques of spectral-interferometry (SI) and chromatic-confocal microscopy (CCM). Measuring the optical interference in the spectral-domain allows for the detection of a reflecting or scattering object’s depth position, without the necessity of a mechanical axial-scan. Focusing the white-light detection field with a microscope objective combined with a diffractive optical element leads to an expansion of the axial-range of the sensor beyond the limited depth-of-focus, imposed by the numerical aperture (NA) of the focusing objective. Focusing with a high NA objective and confocally filtering the detection light field causes the reduction of the lateral dimension of the area sampled upon the object. By this, the lateral resolution of the sensor is enhanced and due to the high NA, a high light collection-efficiency is achieved as well. The attained interferometric signals consist of high-contrast wavelets, measured in the optical-frequency domain. The depth position of an investigated point of the object is given by the modulation-period of the wavelets. Therefore, unlike in CCM, positionwavelength referencing is not necessary.