Parallel phase shift interferometric detection systems were developed using polarized interferometry, three detectors and multiple wavelengths. In phase shift interferometry (PSI) several phase shifted interference images are usually acquired in a sequence and are algebraically combined to extract the phase information. However, phase imaging is limited both by the 2π phase modulo limiting the ability to map structures with heights only up to half the source's wavelength i.e. several hundreds of nm, and also by error induced by the movements of the sample between the acquisitions of phase shifted interference images. Several approaches for dealing with these limitations have been developed that provided only a limited solution, e.g. using a beat wavelength interferogram by a two wavelength illumination but that is more sensitive to phase noise and thus less accurate and parallel PSI in which all phase shifted images are acquired simultaneously but that does not resolve the height limitation. We have developed a combined and improved technique for parallel PSI and three wavelength illumination enabling overcoming both limitations without elevating phase noise sensitivity. Several bench prototypes were built: some allowing video rate 3D imaging of moving samples such as biological live samples or high throughput scanning of metrology samples with nm scale resolution, and others allowing single point very high speed axial motion tracking and vibrometry with sub-nm scale resolution and max step height of few tens of µm.
1. Michael Ney, Avner Safrani, Ibrahim Abdulhalim, Instantaneous high-resolution focus tracking and a vibrometery system using parallel phase shift interferometry, J. Opt. A (Letters) 18, 09LT05 (5pp) (2016).
2. Michael Ney, Avner Safrani, Ibrahim Abdulhalim, Three wavelengths parallel phase-shift interferometry for real-time focus tracking and vibration measurement, Optics Letter 42, 719-22 (2017).
3. Avner Safrani and Ibrahim Abdulhalim, High speed 3D imaging using two wavelengths parallel phase shift interferometry, Optics Letters 40, 4651-4 (2015).
4. Avner Safrani and Ibrahim Abdulhalim, Full field parallel interferometry coherence probe microscope for high speed optical metrology, Appl. Opt. 54, 5083-87 (2015).
5. Avner Safrani and I. Abdulhalim, Real Time, Phase Shift, Interference Microscopy, Optics Letters 39, 5220-23 (2014).
A real time phase shift interference microscopy system is presented using a polarization based Linnik interferometer
operating with three synchronized, phase masked, parallel detectors. Using this method, several important applications
which require high speed and accuracy are demonstrated in 50 volumes per seconds and 2nm height repeatability,
dynamic focusing control, fast sub-nm vibrometry, tilt measurement, submicron roughness measurement, 3D profiling of
fine structures and micro-bumps height uniformity in an integrated semiconductor chip. Using multiple wavelengths
approach we demonstrated phase unwrapped images with topography exceeding few microns.
Following the mature liquid crystals (LCs) display technology, there is a significant interest in implementing these devices into other non-display applications. Hence the emerging field of LC photonics is becoming increasingly active in which the strong electrooptic properties of LCs are harnessed for these applications particularly for imaging such as the use of SLMs, tunable focus lenses, tunable filters and polarization control devices. In this paper we review our recently developed LC devices integrated into full field optical coherence tomography system, into multi-spectral skin diagnosis system and in extended depth of focus imaging system.
Spectropolarimetric skin imaging is becoming an attractive technique for early detection of skin cancer. Using two liquid crystal retarders in combination with a dual-band passive spectral filter and two linear polarizers, we demonstrate the spectral and polarimetric imaging of skin tissue in the near infrared. Based on this concept, a compact prototype module has been built and is being used for clinical evaluation.
A new method and algorithm for measuring optical linear birefringence is proposed. The method allows the measurement of both the principal axis orientation angle and the retardation simultaneously by a three-step measurement. The average absolute error of the retardation of an achromatic quarter-wave plate (QWP) is found to be better than 10−4 parts of the wavelength over the whole spectrum, and its principal axis system orientation is determined with accuracy better than 0.18 deg. In comparison to other methods, the current technique holds several advantages: wavelength independence, low cost, compact setup, ease of alignment, use of a simple algorithm, no polarization reflectance dependence, and possesses high accuracy. The method was applied also to the measurement of an arbitrary retardation of a sapphire plate and to the assessment of the dynamic retardation of a liquid crystal device.
Liquid crystal (LC) devices exhibit fast and strong tuning and switching capabilities using small voltages and can be
miniaturized thus have a great potential to be used with miniature optical imaging systems for biomedical applications.
LC devices designed specifically for integration into biomedical optical imaging systems are presented. Using a
combination of one or two LC retarders we obtained polarimetric imaging of the skin. LC tunable filters with high
dynamic range and large throughput are designed for hyperspectral imaging and for spectral domain optical coherence
tomography. The designs are based on several concepts both using the classical stack of retarders and using more
modern designs based on single layer in a waveguide or in a Fabry-Perot cavity.