Spectral interferometry and reflectometry used to measure thin films

A new method for a precise measurement of the oscillatory part of phase change on reflection (interferometric phase) from a thin-film structure is presented. The method, which is based on phase retrieval from the spectral interferograms recorded at the output of a slightly dispersive Michelson interferometer, is combined with reflectometry. The interferometric phase of the thin-film structure is measured precisely using a reference sample of known phase change on reflection. The spectral reflectance of the thin-film structure is also measured in the interferometer. The feasibility of the method is confirmed in processing the experimental data for SiO₂ thin film on a silicon wafer of known optical constants. Four samples of the thin film are used and their thicknesses are determined. We confirm very good agreement between the thicknesses obtained from the interferometric phase and reflectance measurements. PACS  07.60.Ly; 68.55.Jk; 78.20.Bh     

Heterodyne spectral interferometry for multidimensional nonlinear spectroscopy of individual quantum systems

A novel implementation of transient nonlinear spectroscopy is presented that allows the study of the transient nonlinear polarization emitted from individual electronic transitions. Both the amplitude and the phase of the polarization are retrieved, permitting the implementation of multidimensional spectroscopy in the excitation pulse delays. The technique is shown to detect mutual coherent coupling in a group of individual, localized excitonic transitions.     

Continuous-wave ultrasound reflectometry for surface roughness imaging applications

Background

Measurement of surface roughness irregularities that result from various sources such as manufacturing processes, surface damage, and corrosion, is an important indicator of product quality for many nondestructive testing (NDT) industries. Many techniques exist, however because of their qualitative, time-consuming and direct-contact modes, it is of some importance to work out new experimental methods and efficient tools for quantitative estimation of surface roughness.

Objective and method

Here we present continuous-wave ultrasound reflectometry (CWUR) as a novel nondestructive modality for imaging and measuring surface roughness in a non-contact mode. In CWUR, voltage variations due to phase shifts in the reflected ultrasound waves are recorded and processed to form an image of surface roughness.

Results

An acrylic test block with surface irregularities ranging from 4.22 μm to 19.05 μm as measured by a coordinate measuring machine (CMM), is scanned by an ultrasound transducer having a diameter of 45 mm, a focal distance of 70 mm, and a central frequency of 3 MHz. It is shown that CWUR technique gives very good agreement with the results obtained through CMM inasmuch as the maximum average percent error is around 11.5%.

Conclusion

Images obtained here demonstrate that CWUR may be used as a powerful non-contact and quantitative tool for nondestructive inspection and imaging of surface irregularities at the micron-size level with an average error of less than 11.5%.     

Multi-colour microscopic interferometry for optical metrology and imaging applications

Interferometry has been widely used for optical metrology and imaging applications because of their precision, reliability, and versatility. Although single-wavelength interferometery can provide high sensitivity and resolution, it has several drawbacks, namely, it fails to quantify large-discontinuities, large-deformations, and shape of unpolished surfaces. Multiple-wavelength techniques have been successfully used to overcome the drawbacks associated with single wavelength analysis. The use of colour CCD camera allows simultaneous acquisition of multiple interferograms. The advances in colour CCD cameras and image processing techniques have made the multi-colour interferometry a faster, simpler, and cost-effective tool for industrial applications. This article reviews the recent advances in multi-colour interferometric techniques and their demanding applications for characterization of micro-systems, non-destructive testing, and bio-imaging applications.     

Developments and applications of conjugate-wave holographic interferometry

Conjugate-wave holographic interferometry is an optical technique which was recently proposed by one of the authors for the measurement, in real time, of in-plane deformation.Basically, the technique consists of projecting, from two symmetrical directions, two real images of an object upon the object itself. If the object deforms, interference fringes are observed on its surface. These fringes give a representation of one in-plane component of the point displacement vector and are independent of the out of plane component.On this paper some aspects of the optical principles underlying the technique are analyzed in deeper detail, and more advanced solutions for their practical implementation are proposed. In addition, a few examples of applications on-plane and not-plane specimens are presented.     

The correlation strength in pion interferometry

Distortions of single-boson spectra and their influence on two-particle correlations are studied. In a simplified simulation the importance of these effects especially in the case of small source sizes is investigated. The apparent correlation strength may be strongly altered, thereby making the interpretation of such a measurement even more difficult.     

Optical heterodyne grating shearing interferometry for long-range positioning applications

We develop a displacement measurement and positioning system with nanometer resolution over the millimeter traveling range. The method is based on a heterodyne grating shearing interferometry, a homemade lock-in amplifier and a servo control loop for displacement sensing and positioning. The quasi-common optical path configuration of our system provides better immunity against environmental disturbances. The experimental results demonstrate that our system can measure small and long displacement with nanometric resolution. The device achieves a positioning resolution of 2.3 nm over a traveling range of 20 mm.     

Heterodyne spectroscopy for astrophysical applications using tunable laser sidebands at 10 microns

A heterodyne system was assembled from a microwave tunable sideband laser, a blackbody source, a gas cell, a CdHgTe photomixer and a filterbank. A measurement of line profiles of CH₃F is presented and compared with absorption measurements. System sensitivity is sufficient for high resolution measurement of fine structure lines from astronomical objects, though falling short by a factor of 12, when compared with the most sensitive astronomical heterodyne spectrometers. The usefulness of such a system for astrophysical applications is discussed.     

Theoretical basis for a new subnatural spectroscopy via correlation interferometry

A new line-narrowing effect in coincidence interferometry yielding subnatural resolution of atomic transition frequencies is proposed and analyzed. The approach utilizes second-order photon correlation properties of the radiation field. This is in contrast to the first-order measurements associated with time delay spectroscopy, which is known to yield subnatural resolution. Connections between the two techniques are investigated.Dedicated to the memory of Professor Julian Schwinger, a role model for us all     

Differential spectral interferometry: an imaging technique for biomedical applications

Differential spectral interferometry (DSI), a novel method of biomedical imaging that combines the high dynamic range of optical coherence tomography (OCT) with inherently parallel low-bandwidth image acquisition of spectral interferometry (SI), is described. DSI efficiently removes the deleterious dc background inherent in SI measurements while maintaining the parallel nature of SI. We demonstrate DSI on both synthetic and biological samples. Because DSI preserves the low-bandwidth, parallel nature of SI, it is competitive with OCT for biomedical applications in terms of image quality and acquisition rate.     

Heterodyne receiver PICs as the first monolithically integrated tunable receivers for OFDM system applications

The state of the art in the fabrication of heterodyne receiver photonic integrated circuits (PICs) is described and in particular the results and experiences of the first fabrication of polarization-insensitive heterodyne receiver PICs are emphasized. The fabrication is based on a versatile integration concept with the potential also to fabricate other PIC architectures with different functionalities by only a single fabrication process.     

Generalized metric spaces for correlation fringes and applications

A novel conception and its applications, the generalized metric for correlation fringes, are presented, which can be used to develop and analyze the relevant algorithms. The relationship between the metric and the correlation fringes representation is examined and the generalized metric is defined. The theoretical analysis of traditional algorithms for correlation fringes indicates that all of them can be regarded as the generalized metrics. In addition, the generalized metric for correlation fringes is applied in developing a new algorithm. A novel generalized metric for correlation fringes based on cross entropy is presented and is proved by theoretical derivation and experimental verification. All the investigations show that it is reasonable and valid to define the generalized metric for correlation fringes in digital speckle pattern interferometry (DSPI). The fringes obtained by cross-entropy metric can be used to represent the same desired information by subtracting. There are different vector function structures among the generalized metrics, which directly influence the quality of fringes and the difficulty in post-processing.     

Double-image encryption based on joint transform correlation and phase-shifting interferometry

An image encryption method combining the joint transform correlator (JTC) architecture with phaseshifting interferometry to realize double random-phase encoding is proposed. The encrypted field and the decrypting key are registered as holograms by phase-shifting interferometry. This method can encrypt two images simultaneously to improve the encryption efficiency of the methods based on JTC architecture, and eliminate the system alignment constraint of the methods based on Mach-Zehnder interferometer (MZI)architecture. Its feasibility and validity are verified by computer simulations. Moreover, image encryption and decryption can be achieved at high speed optically or digitally. The encrypted data are suitable for Internet transmission.     

Recent contribution in color interferometry and applications to high-speed flows

Recent improvements brought to color interferometry for analyzing high-speed flows are described through different applications. First, the optical technique based on differential interferometry using a polarized white light and one or two Wollaston prisms allows to record high-speed interferograms of the flow downstream of a circular cylinder. Then, this technique has been applied to axisymmetric flows for studying an interaction between a supersonic hot jet and a coaxial supersonic flow. Another application concerns the study of hypersonic flows using Wollaston prisms with a large birefringence angle. Finally, the analysis of gaseous mixture and the evolution of two-gases interface submitted to an acceleration is presented. Interferograms analysis is made from a modeling of interference fringes versus the optical path difference which allows to easily extract quantitative information of the gas density. In order to obtain absolute measurements of the gas density, real-time holographic interferometry has been developed using a three-color laser source and a panchromatic holographic plate. The technique generates the achromatic white fringe which makes the zero order of interference fringes easy to identify. An application is presented in a 2D subsonic wind tunnel, in which the unsteady wake flow past a cylinder is recorded at high framing rate. In this optical setup, transmission holograms are used. As a conclusion, an approach is proposed to analyze the 3D flows from real-time color holographic interferometry using reflection holograms and the problems to solve are described.     

UV-VIS absorption spectroscopy of large molecules for applications in matter wave interferometry

We study the optical properties of various large molecules with respect to their suitability for new matter wave interference and detection schemes. Optical phase gratings for molecules will only be compatible with a sufficiently small absorption cross section visible while optical detection schemes may exploit strong UV resonances. We compare UV-VIS spectra of various biomolecules, such as amino acids, polypeptides, and proteins, with those of new perfluoroalkylated molecules and carbon nanotubes, and we discuss their suitability for coherent matter wave experiments.     

Optical‐fiber microcoil waveguides and resonators and their applications for interferometry and sensing

In this work, recent progress in the theoretical and experimental studies of optical‐fiber microcoil waveguides and resonators, as well as their various applications are reviewed. In particular, the focus is set on sensing and interferometry applications. It is shown that due to its inherently low propagation and fiber‐coupling losses, fiber‐microcoil based sensors and interferometers offer substantial enhancement of sensitivity and compactness compared to other types of devices. Recent progress in the realization and experimental characterization of such structures is presented and the theoretical tools to analyze the impact of real‐world nonuniformities on the characteristics of fiber‐microcoil structures are provided.     

光子相关光谱技术及其应用

讨论了光子相关光谱（PCS）技术的原理和测量过程，介绍了光子相关光谱方法在生物工程、药物学以及微生物领域的应用。