Non-interferometric Method Research Articles

Automated phase characterization and adaptive pulse compression using multiphoton intrapulse interference phase scan in air

We introduce a non-interferometric single beam method for automated spectral phase characterization and adaptive pulse compression of amplified ultrashort femtosecond pulses taking advantage of third order harmonic generation in air. This new method, air-MIIPS, compensates high-order phase distortions based on multiphoton intrapulse interference phase scan (MIIPS).

Wavefront correction of spatial light modulators using an optical vortex image

We present a fast and flexible non-interferometric method for the correction of small surface deviations on spatial light modulators, based on the Gerchberg-Saxton algorithm. The surface distortion information is extracted from the shape of a single optical vortex, which is created by the light modulator. The method can be implemented in optical tweezers systems for an optimization of trapping fields, or in an imaging system for an optimization of the point-spread-function of the entire image path.

Pseudoheterodyne detection for background-free near-field spectroscopy

The authors present a detection technique for scattering-type near-field optical microscopy capable of background interference elimination in the entire near-UV to far-IR spectral range. It simultaneously measures near-field optical signal amplitude and phase by interferometric detection of scattered light utilizing a phase-modulated reference wave. They compare its background suppression efficiency to other known methods and experimentally show that it provides a reliable near-field optical material contrast even in the case where both noninterferometric and homodyne interferometric detection methods fail.

Inferring the time-dependent complex Ginzburg-Landau equation from modulus data

We present a formalism for inferring the equation of evolution of a complex wave field that is known to obey an otherwise unspecified -dimensional time-dependent complex Ginzburg-Landau equation, given field moduli over various closely spaced planes. The phase of the complex wave field is retrieved via a noninterferometric method, and all terms in the equation of evolution are determined using only the magnitude of the complex wave field. The formalism is tested using simulated data for a generalized nonlinear system with a single-component complex wave field. The method can be generalized to multicomponent complex fields.

Noninterferometric and nontomographic iterative method for field retrieval.

A new method of field recovery is proposed based on the fact that an arbitrary light beam can be expressed as a finite sum over orthogonal field distributions with unknown coefficients. If these field distributions are eigenmodes of a specific waveguide, the coefficients of the field decomposition in orthogonal eigenmodes can be determined iteratively when the unknown field is passed through a series of waveguides that support an increasing number of modes. This series of waveguides can be replaced by a single reconfigurable electro-optic waveguide, which one can use to recover the unknown field by performing only intensity measurements.

Multiphoton intrapulse interference. IV. Ultrashort laser pulse spectral phase characterization and compensation.

We introduce a noninterferometric single beam method to characterize and compensate the spectral phase of ultrashort femtosecond pulses accurately. The method uses a pulse shaper that scans calibrated phase functions to determine the unknown spectral phase of a pulse. The pulse shaper can then be used to synthesize arbitrary phase femtosecond pulses or it can introduce a compensating spectral phase to obtain transform-limited pulses. This method is ideally suited for the generation of tailored spectral phase functions required for coherent control experiments.

Understanding magnetic structures in permanent magnets via in situ Lorentz microscopy, interferometric and non-interferometric phase-reconstructions

We present our observations of field- and orientation-dependence of magnetic domains and their reversal nucleation at grain boundaries in polycrystalline Nd2Fe14B, using Fresnel- and Foucault-Lorentz microscopy. The local magnetization associated with the domain and domain-wall in Nd2Fe14B and in precipitated Fe particles was mapped using an interferometric holography as well as a novel non-interferometric method based on the 'transport of intensity' equation.

In-situ Lorentz TEM cooling study of magnetic domain configurations in Ni/sub 2/MnGa

Magnetic domain configurations in the ferromagnetic shape memory alloy Ni/sub 2/MnGa are analyzed by means of Lorentz microscopy and noninterferometric phase reconstruction methods. Domain structures in the cubic phase consist of cross-tie walls in the thinnest portions of the foil, and more complex configurations in thicker regions. At low temperature, the magnetization configurations change as the structure transforms martensitically to a tetragonal phase. A simple model for the magnetization changes is proposed.

Pulse characterization at 1.5 μm using time-resolved optical gating based on dispersive propagation

This letter demonstrates the use of time-resolved optical-gating based on dispersive propagation to characterize a semiconductor mode-locked laser emitting picosecond pulses at a wavelength of 1.5 /spl mu/m. DP-TROG is a new noninterferometric method for characterizing ultra-short optical pulses in amplitude and phase without the need for a short optical gating pulse. We describe and give recommendations for the reconstruction of the pulse properties from the set of measured autocorrelation traces and the intensity spectrum.

Measurement of energy density and duration of ultrashort incoherent light pulses with the aid of liquid crystals

We discuss new possibilities for the measurement of short laser pulses with the aid of liquid crystals: the competingly acting waves (CAW) method and the linear-optical pulse overlap (LOPO) method. CAW is a non-interferometric method providing both the peak energy density of a pulse and its duration in a simple, single shot measurement. LOPO allows measurement of ultra-short pulse duration with no need for nonlinear optical materials and phenomena. We also show the possibility of utilising the electrically controlled birefringence of liquid crystals to replace the opto-mechanical delay lines.

Time-resolved optical gating based on dispersive propagation: a new method to characterize optical pulses

We introduce the technique of time-resolved optical gating (TROG) based on dispersive propagation (DP), a new noninterferometric method for characterizing ultrashort optical pulses in amplitude and phase without the need for a short optical gating pulse. TROG is similar to frequency-resolved optical gating except that the role of time and frequency is interchanged. For the DP-TROG geometry, we show that measurements of the autocorrelation trace of the pulse after propagation through a medium with variable dispersion together with a single measurement of its intensity spectrum contain sufficient information to reconstruct the pulse in amplitude and phase. Pulse reconstruction for this DP-TROG geometry works very well even for the case of a nonlinearly chirped double pulse. Compared with other methods, DP-TROG does not introduce an ambiguity in the direction of time for the pulse. Due to its simplicity and improved sensitivity. DP-TROC is expected to be useful in characterizing low-energy pulses.

Non-interferometric methods of phase estimation for application in optical tomography

Abstract We describe here two non-interferometric methods for the estimation of the phase of transmitted wavefronts through refracting objects. The phase of the wavefronts obtained is used to reconstruct either the refractive index distribution of the objects or their contours. Refraction corrected reconstructions are obtained by the application of an iterative loop incorporating digital ray tracing for forward propagation and a modified filtered back projection (FBP) for reconstruction. The FBP is modified to take into account non-straight path propagation of light through the object. When the iteration stagnates, the difference between the projection data and an estimate of it obtained by ray tracing through the final reconstruction is reconstructed using a diffraction tomography algorithm. The reconstruction so obtained, viewed as a correction term, is added to the estimate of the object from the loop to obtain an improved final refractive index reconstruction.

Non-interferometric methods of phase estimation for application in optical tomography

We describe here two non-interferometric methods for the estimation of the phase of transmitted wavefronts through refracting objects. The phase of the wavefronts obtained is used to reconstruct either the refractive index distribution of the objects or their contours. Refraction corrected reconstructions are obtained by the application of an iterative loop incorporating digital ray tracing for forward propagation and a modified filtered back projection (FBP) for reconstruction. The FBP is modified to take into account non-straight path propagation of light through the object. When the iteration stagnates, the difference between the projection data and an estimate of it obtained by ray tracing through the final reconstruction is reconstructed using a diffraction tomography algorithm. The reconstruction so obtained, viewed as a correction term, is added to the estimate of the object from the loop to obtain an improved final refractive index reconstruction.

Testing aspheric surfaces: simple method with a circular stop

As an extension of the knife-edge test, a noninterferometric method for inspecting circularly symmetric aspheres is proposed in which the test surface is illuminated by a spherical wave. When a small circular stop is placed around the curvature center of the best-fitting sphere, only rays characteristic for the deviation from a perfect sphere remain unobstructed. An image of the tested surface is thereby obtained, showing light and dark regions whose boundaries are correlated to the surface profile, the stop size, and the stop position along the symmetry axis. The experiment has been carried out with a paraboloid.

Potential and vortex features of optical speckle fields and visualization of wave-front singularities

The feasibility of noninterferometric methods to measure phase distribution in a laser beam cross section for visualization of the vortex dislocations of an optical speckle-field wave front is analyzed. Peculiarities of the phase retrieved from the measured intensity distribution (the phase problem in optics) and from the wave-front slopes measured by a Hartmann sensor are discussed. A concept of the vortex and the potential parts of the phase is introduced. An analytic formula to retrieve the potential phase from the measured intensity has been obtained. We show that the considered means of measurements allow the positions of the dislocation centers to be sensed and the spatial configuration of the intensity zero lines to be reconstructed.

Conic constant determination using axial intensity scans

Axial intensity scans provide a noninterferometric method for measuring aberration content of a focused beam. Applications of the technique include the determination of the conic constant of aspheric mirrors (without the need for a null lens).

Droplet profiles obtained from the intensity distribution of refraction patterns

A noninterferometric method for obtaining profiles of axially symmetric transparent liquid droplets is described. The drops are illuminated along the symmetry axis by a uniform parallel beam whose intensity distribution is recorded at the focal plane of a lens placed behind the drop. In some conditions and within the geometrical optics approach, it is possible to reconstruct the profile of the drop from this intensity distribution except for the length scale factor, which, if necessary, may be provided by an additional simple measurement. Because of CCD cameras and digital image processing, this method is an interesting alternative technique for measuring drop profile shapes with considerable accuracy when interferometry is unwieldy. We also analyze the diffraction features of the intensity distribution to clarify the extent that they affect the approach that we used and to establish additional information that they may provide.

Nanometer-resolution distance measurement with a noninterferometric method

We have developed a noninterferometric technique for high-resolution distance measurement (optical ranging). The technique utilizes the fact that the wavelength of a broadband cw laser can be changed by external feedback. By placing the ranging target near the focal point of a microscope objective, we can make the feedback from the target, hence the laser wavelength, sensitive to the target position. The target position is determined from the laser wavelength with great resolution. In our experiments a 20-nm resolution is obtained. The resolution is limited by the instrumental resolution and mechanical stability of the experimental setup.

Noninterferometric reconstruction of optical-field correlations.

A noninterferometric method for reconstructing the second-order correlations of a partially coherent optical field is described. It is assumed that the field propagates close to one particular direction, so that the paraxial approximation may be used, and that the field correlations in some cross section may be well approximated by the quasihomogeneous model. Two reconstruction formulas are derived which uniquely determine the cross-spectral density function, characterizing the correlations, from knowledge of the spatial distribution of the spectral density in several parallel planes.