High-sensitivity and a high-speed nanoscale measurement is an important subject in modern industry, especially when analysis of high-speed moving nanoscale objects on a surface is required. Several objectives in this direction can be achieved by using singular beam microscopy, which we investigate experimentally for the examination of small phase steps. We discuss the challenges of rigorous modeling of experiments employing high-numerical-aperture illumination and describe experimental results performed with a medium numerical aperture of 0.55. The investigated equivalent phase step heights reached as low as 10 nm (about 1/15 rad).
A laser resonator configuration is proposed in which the fundamental oscillating mode is an odd mode with a line
singularity. The resonator is based on the replacement of one reflector by a bi-lens split mirror. The beam emitted by
such a laser is an ideal source for the recently introduced singular beam microscopic procedure. We numerically
investigate resonators with convex and concave faces of the reflector. It is shown that resonators of the latter type of
reflectors have higher effectiveness in shaping modes with linear singularity. Their selectivity is also higher, than
resonators with roof-mirrors that were investigated earlier.
Investigation of nanoscale objects is becoming increasingly important with development of modern nanotechnology
related industries. Under certain conditions, some information on the investigated object can be obtained in the forward
scattering far field when the object is scanned by a focused beam. The sensitivity of the far field based measurements
depends on a number of factors including the shape of the investigated object. In this work we present a case study
comparing far field response in scanning mode. The response sensitivity for nano-scale phase objects of different shapes
and different phase volumes under various illuminating conditions is discussed. We perform a paraxial simulation with
investigated phase objects represented as thin optical elements: free standing and as a part of a surface.
The introduction of an uncooled microbolometer image sensor about a decade ago
enabled cost reduction of IR cameras. As a result, the available markets grew both in
military and civilian applications. Since then, the price of microbolometer was gradually
reduced due to introduction of devices with smaller pixel, maturity of the technology and
quantity growth. However, the requirement for a vacuum package still limits the price of
microbolometer based cameras to several thousands of dollars. Sirica's novel wavelength
conversion technology aims at breaking this paradigm by being uncooled and vacuumless,
lowering IR camera prices by an order of magnitude, opening the way to new mass
markets.
Sirica's proprietary IR-to-Visible/NIR conversion layer allows for low-cost high
performance LWIR detector with no requirement for cooling and vacuum packaging.
In the last years, the development efforts focused on development of the conversion
media. Recently, a parallel effort for the integration of the conversion layer together with
other detector components has started. Packaging of detector components, such as
conversion layer, pumping light source, dichroic filter, and their coupling with silicon
CMOS image sensor have great importance from a price-performance point of view.
According to the company's business-development roadmap, the detector prototype
should be available during the first quarter of 2010.
Shaping laser beams within the laser cavity can improve the laser power efficiency and allows the generation of
predetermined beam structures suitable for various applications such as metrology, lithography and particle
manipulation. In this work we study a resonator in which one of the mirrors is replaced by a conical reflector and derive
resonator parameters for required beam selections. For example, we show that choosing a negative cone angle can lead to
oscillation on pure high-order modes corresponding to the first and second order Bessel functions in the resonator
integral equation kernels. These modes possess a distinct zero intensity on the axis that can be exploited for applications
such as singular beam metrology and particle manipulation. To generate the specific beam structures we found optimal cone angles and mirror sizes for stable resonators with two configurations, close to flat and to concentric. These optimal conditions were derived by requiring that the selected mode has minimal diffraction loss. It is shown that the selection of these higher-order modes is more efficient in the concentric configuration.
Rigorous vector analysis of high numerical aperture optical systems encounters severe difficulties. While existing
analytic methods, based on the Richards-Wolf approach, allow focusing of nearly planar incident wavefronts, these
methods break down for beams possessing considerable phase jumps, such as beams containing phase singularities. This
work was motivated by the need to analyze a recently introduced metrological application of singular beams that
demonstrated an experimental sensitivity of 20nm under a moderate numerical aperture of 0.4. One of the possibilities to
obtain even better sensitivity is by increasing the numerical aperture of the optical system. In this work we address the
issue of high numerical aperture focusing of the involved singular beams. Our solution exploits the superposition
principle to evaluate the three dimensional focal distribution of the electromagnetic field provided the illuminating
wavefront can be described as having piecewise quasi constant phase. A brief overview of singular beam microscopy is
followed by deeper discussion of the involved high numerical aperture focusing issue. Further, a few examples of
different singular beam focal field distributions are presented.
The Richards-Wolf approach to analyze tight focusing by high-numerical-aperture aplanatic optical systems was designed to treat incident waves having a planar (or negligibly curved) wavefront at the entrance pupil. In this paper we extend the approach to incorporate also wavefronts with piecewise quasi-constant phase. The evaluation of the field distribution in the vicinity of the geometrical focus is accomplished by linear superposition of the contributions from all the segments with quasi-constant phase. As an application example, a tightly focused optical field is evaluated for a -phase-step-modulated incident wavefront.
Laser beams containing singularities are gaining increased interest for applications in metrology, particle manipulation and other technological paradigms. While these beams are usually generated by external modulation of a fundamental Gaussian laser beam, it is advantageous to generate them directly within the laser resonator whenever possible. In this paper we propose and investigate the mechanism of selecting a mode possessing a linear singularity using strong diffraction coupling of two adjacent resonators using a bi-prism-like element.
Quickly developing nanotechnology drives the industrial need for fast but sensitive nano-scale feature detection and
evaluation. In this work we bypass the diffraction limit for achieving nanoscale sensitivity by introducing optical
singularities into the illuminating beam for a modified laser scanning microscopic architecture. A good correspondence
was obtained between laboratory experiments and corresponding simulations that indicated a theoretical potential of 1nm
sensitivity under a practical signal to noise ratio of 30dB. For analysis of the experimental and simulation results, two
simple but effective algorithms were developed. A significant improvement of signal to noise ratio in the optical system
with coherent light illumination can be achieved by utilization a highly redundant data collected during experiments. Our
experimental results validate achievable sensitivity down to 20nm. The unique combination of nano-scale sensitivity
together with implementation simplicity and on-line, real-time analysis capability make Singular Beam Microscopy a
valuable industrial analytic method.
New methods of laser metrology (interferometry and microscopy) based on applications of beams
with special structures provide increased resolution and efficiency. To generate a beam with linear
singularity (dark beam) we recently proposed a beam shaping method using a bi-prism-like element within
the laser resonator. There we have studied resonators that are traditionally designed to oscillate on the
fundamental mode designed within the range of configuration parameters, 0.5⩽G⩽1.
In the present work we extend the approach and show that the choice of specific configurations,
outside the above range of configuration parameters, can lead to much better results for our application.
This is the case in particular for an approximately semi-concentric resonator (G ~ -1).The optimal dark
beam is obtained for a bi-prism angle about twice that obtained for the earlier configurations. For this case
the difference between the losses of the first odd mode and other modes is 0.12-0.15, which is adequate for
oscillation on this mode in lasers with any type of active media.
Structured light beams have useful attributes to different scientific, industrial and technological applications. Of particular interest are light distributions containing well-defined dark regions. Such distributions are usually called - dark beams, black beams, "doughnut" mode and light bottles and have widely known applications in optical metrology and atom physics. The conventional way to generate these distributions is by various diffractive optical elements and also by special laser cavity design. In this paper we present a simple method, which is based on the Bragg selectivity of volume gratings. Initial experimental results show promising potentials of such approach.
In a recent work it was demonstrated that efficient laser mode selection can be accomplished by replacing one of the laser mirrors by a bi-prism-like (flat-roof) reflector. In that work the objective was to generate a pure "dark beam" (a laser beam with a dark central region) for high resolution metrological applications. With the same objective in mind, in this work we present a new approach that leads to significant improvement of laser performance. This approach is based on an earlier work where a narrow amplitude mask over the middle of a conventional laser mirror was used to suppress the zero-order mode to facilitate oscillation of the first-order mode possessing the required characteristics. Starting from a similar configuration, in the present work we show that the performance can be optimized by combining a partially transmitting amplitude mask with a bi-prism-like reflector. Numerical simulations predict mode selectivity enhancement of at least a factor of 3 as compared to laser resonators with bi-prism-like reflectors alone.
Intra-cavity beam shaping, if properly implemented, is much more energy efficient and produces cleaner beams than the traditional external spatial modulation. Our special interest in this work is the generation of high-quality dark, or singular beams, for metrological applications. We show that bi-prism like reflectors possessing a central phase excursion within the range ±(0.3-1) π, can significantly alter the relative diffraction losses among the various oscillating modes, enabling efficient mode selection and shaping.
A novel approach to optical surface metrology in the nano-scale region was introduced recently. The approach is based on scanning of the interrogated space by specially structured light distributions and the analysis of the scattered light in the far field. For high resolution metrology, various dark beams as the scanning beams were found to be most effective. After a short overview of the measuring procedure, this paper addresses appropriate optical wave front engineering methods. These include the employment of diffractive optical elements designed for wave engineering within a three-dimensional section of space as well as laser beam structuring within the laser cavity.
In earlier publications, it was shown that scanning of surfaces by dark beams can be exploited for sub-wavelength feature analysis. In this work, we present vector simulations based in Rigorous Coupled-Wave Analysis with the purpose to estimate the expected resolution of the method, both lateral (feature size) and axial (height). The dark beam used in this study has a line singularity generated by a π-phase step positioned in a Gaussian beam. Various combinations of the illumination and detection nuFmerical apertures (from NA=0.2 to NA=0.8) and different surface features were studied. Polarization effects which become significant at high numerical apetures, were considered as an additional source of information for the analysis. In the case of a sub-wavelength feature on an ideal surface, the resolution of the method is limited only by the electronics noise. In particular, under a reasonable assumption of a 105 signal to noise ratio, it is possible to detect a 0.2 nm step.
Interest in beams containing phase singularities (dark beams) is evolving as applications are being realized, in particular for high-resolution microscopy and measurements. While these dark beams are usually generated with the help of diffractive elements, in this paper two new approaches for the generation of dark beams within the laser cavity are proposed and investigated. Simulations demonstrate that distributions similar to dark beams can be obtained by various laser modes.
Surface feature evaluation with resolution beyond the classical diffraction limit can be achieved by a combined space--frequency representation of the scattered field. This was demonstrated in a measuring procedure where the surface was consecutively illuminated by a collection of focused beams and the diffracted data was measured in the far field. Mathematically, if the focused beam has a Gaussian profile, the optical system implements a Gabor transform. Other transformations, such as wavelet transforms can be obtained by properly structuring the illuminating beam. This work presents an approach where structured beams at several wavelengths are used. This additional information gathered by this procedure allows an increased resolution and the reduction of ambiguities that may occur in the analysis of single wavelength measurements.
Reliable in-line and in-situ measurement of structure of highly polished surfaces remains a major challenge for the modern industry. Evaluation of the wavefront of a scanning laser beam reflected from a surface allows one to establish a direct correlation between the statistics of the optical signal and the surface roughness. Phase structuring of the laser beam greatly increases the height sensitivity down to the nanometer level. High sampling rate allows one to collect a very large number of sampled data and provide a complete analysis of the surface structure rather than a single parameter such as the rms roughness.
The field of light structuring in extended 3D regions of space is making significant progress in the design, implementation and applications. Some of the physical principles and algorithmic aspects will be indicated and several applications will be discussed. Applications related to fundamental aspects of light propagation include the generation of non-expanding beams and beam-arrays. While several technological applications of the above mentioned light distributions can be foreseen, some were also investigated. These include surface profile measurements with resolution exceeding classical diffraction limits. Another area of application is in special lithography where the possibility of extending the depth of focus of light structures can be utilized. The algorithms used in this work are designed to exploit the information content of the recording device in an optimized way. This enables the generation of diffractive optical elements on low resolution devices, such as presently available spatial light modulators. Accordingly, dynamically programmable light distributions can be implemented for various applications such as free-space interconnections, display and measuring procedures.
Diffractive elements are designed to synthesize special purpose distributions of light which extend in three-dimensional domains. These distributions present unique physical properties: high directionality, diffraction limited spot-size, propagation invariance, extinction and regeneration. The diffractive elements are iteratively designed and exhibit an efficient utilization of the information capacity. Experimental results demonstrate good agreement with simulations.
A wavefront sensor is supposed to analyze the phase distribution of a wave without any external reference as used in most conventional interferometric systems. It is shown here that an efficient wavefront sensor can be implemented by an array of two-beam common path inversion interferometers. Each element of the array consists of two Fresnel lenses in a confocal configuration. The wavefront data can be extracted from a superposition of the zero- order, undiffracted wave and the twice diffracted first order wave. The result is a high sensitivity, compact and stable interferometric wavefront sensor.
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