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We present a new scheme to produce a tunable converge elliptical optical vortex (EOV) with a phase-only element: elliptical helical lens (EHL), which is studied theoretically and experimentally. As a result, the properties of converge EOVs can be controlled by adjusting the parameters of EHL. The topological charges of the EOVs can be directly read from the received intensity pattern. Because EHL is a hologram programmed in space light modulator (SLM), converge EOVs can be controlled just by reprogramming the SLM instead of replacing actual instruments. This work has potential applications in particle manipulation, as well as generation of OAM-entangled photons. [ABSTRACT FROM AUTHOR]

The auto-focusing and auto-healing profiles of linearly polarized ring Airy Gaussian vortex (RAiGV) beams in linear media are investigated experimentally based on spatial light modulators and computer-generated holograms. It is found that the parameters of incident beams greatly affect the auto-focusing profiles of RAiGV. The focal length increases as the radius of the primary ring, scaling factor and waist radius increases, and the focal length decreases slightly as topological charges increase. The peak intensity at focal point increases with the increasing topological charges and waist radius, or with the decreasing scaling factor and the radius of the primary ring. The phase singularity of the RAiGV beams remains unchanged during propagation. The RAiGV beams also exhibit remarkable resilience against perturbations and tend to reconstruct its intensity sharp. Meanwhile, the abruptly auto-focusing property can be controlled by blocking few inner or outer rings of the RAiGV beams. These studies provide useful insight in the study of Airy vortex beam and its further applications. [ABSTRACT FROM AUTHOR]

Debris deposited around laser-processed structures is a critical issue in high-precision laser processing and should be removed. We demonstrated a new debris removal method that is performed during laser processing. A line-focused beam that is radiated onto a target material simultaneously with a processing beam sweeps away the debris generated by laser ablation. Two physical processes are involved: One is direct photon excitation of the attached debris, similar to laser ablation, due to a smaller ablation threshold of the debris, and the other is blowing away the debris with a laser-induced pressure wave. The laser processing setup for debris sweeping has a simple and practical configuration composed of beam transmission optics from a laser source to the target and a spatial light modulator that displays a computer-generated hologram. This in-process debris removal method has the advantages of needing no additional equipment other than the optics, no additional operations, no special materials, and no specific operating environment. [ABSTRACT FROM AUTHOR]

We demonstrate compensation for the spherical aberration due to the refractive index mismatch that occurs when a laser beam is focused into a thick arsenic trisulfide (As $$_2$$S $$_3$$) film with a high numerical aperture objective. The effects of the aberration at different focal depths on the point spread function have been calculated numerically and the axial response method shown to be a useful measure for compensating the spherical aberration. We show that with the addition of adaptive optics based on a spatial light modulator, the aberration can be significantly reduced, resulting in an increase in peak intensity by a factor of 2.4 and a decrease in axial elongation by a factor of 2.2. [ABSTRACT FROM AUTHOR]

We report experimental generation of a partially coherent Laguerre-Gaussian beam with mode orders 0 and l (i.e., LG beam) using a rotating ground-glass plate and a spatial light modulator. Focusing properties of the generated beam are studied both theoretically and experimentally. It is found that the focused intensity of the LG beam is shaped through varying the initial spatial coherence, and our experimental results agree well with the theoretical predictions. Our results will be useful in particle trapping and free-space optical communications. [ABSTRACT FROM AUTHOR]

We propose the first experimental approach for both generation and characterization of high quality Devil's vortex-lenses. These new type of lenses, able to produce a sequence of optical vortices, are addressed onto a programmable spatial light modulator (SLM) operating in phase-only modulation. The static aberrations arising by the lack of flatness of the SLM display are characterized and mostly compensated by using a Shack-Hartmann wavefront sensor. The analysis of the residual aberrations and their effect on the vortex-lens performance are studied. [ABSTRACT FROM AUTHOR]

In this paper we demonstrate experimentally the intra-cavity generation of a coherent superposition of Laguerre-Gaussian modes of zero radial order but opposite azimuthal order. The superposition is created with a simple intra-cavity stop that creates equal losses for the two azimuthal modes, and we show that by adjustment of the stop we can produce modes up to azimuthal order 8. The fact that we have a coherent superposition rather than an incoherent superposition is verified by intensity measurements, propagation measurements and a decomposition of the field by an inner product executed on a phase-only spatial light modulator. Such fields have relevance in quantum information and optical trapping. [ABSTRACT FROM AUTHOR]

Intensity patterns for optical lithography are synthesized with phase-controlled multi-beam interference. By using a programmable spatial light modulator, reconfigurable intensity patterns can be generated and optimized to approach an objective intensity distribution. A self-adaptive annealing algorithm is applied to feedback control to obtain the predetermined intensity distribution. Typical photonic crystal with zigzag waveguides and micro-cavities are fabricated with a one-step-exposure lithographic technique. [ABSTRACT FROM AUTHOR]

Based on the recently formulated unified theory of coherence and polarization of light, we explore the behavior of the intensity-intensity correlations and the auxiliary quantity called the degree of cross-polarization in stochastic electromagnetic beams upon their passage through the devices of polarization optics. In particular, the effects of deterministic devices (such as polarizers, absorbers, compensators, and rotators) as well as of random devices (such as spatial light modulators) on passing beams are investigated. Our results may find applications in polarimetric communications, imaging and sensing. [ABSTRACT FROM AUTHOR]

We propose a versatile arrangement for the trapping and manipulation of single atoms in optical tweezers formed by the direct image of a spatial light modulator (SLM). The scheme incorporates a high numerical aperture microscope to map the intensity distribution of a SLM onto a cloud of cold atoms. The regions of high intensity act as optical dipole-force traps. With a SLM fast enough to modify the trapping potential in real time, this technique is well suited for the controlled addressing and manipulation of arbitrarily selected atoms. [ABSTRACT FROM AUTHOR]

We report on the monolithic integration of frequency converter and amplitude modulator in a single lithium niobate (LiNbO) chip by the use of focussed ultrashort laser pulses. The waveguiding structures are obtained by femtosecond-laser induced internal modification and the electrodes are ablated out of a gold-layer sputtered onto the sample surface. [ABSTRACT FROM AUTHOR]

Parallel femtosecond refractive index laser inscription of clinical grade poly(methyl methacrylate) (PMMA) at 775 nm, 170 fs pulselength is demonstrated with multiple low fluence beams generated with the aid of a spatial light modulator. Using optimised computer-generated holograms (CGHs), 16 diffracted near identical beams were focused simultaneously within bulk PMMA to create a series of 19 μm pitch, 5 mm×5 mm×1-4 mm thick volume phase gratings at high speed. First order diffraction efficiency rises with grating thickness in accord with diffraction theory, reaching 75% at the first Bragg angle (4 mm thick) with fabrication time around 1 hour. By carefully stitching filamentary modifications while eliminating effects such as pulse front tilt during inscription, gratings exhibit high uniformity, which has not been achieved previously using femtosecond inscription. Highly uniform modification is exhibited throughout the material consistent with the observed excellent angular selectivity and low background scatter and quantitative comparison with first order diffraction theory is satisfactory. The diffraction efficiency and hence refractive index profile shows a temporal behaviour related to the material response after exposure. Simultaneous 3D modification at different depths is also demonstrated, highlighting the potential of creating complex 3D integrated optical circuits at high speed through the application of CGHs. [ABSTRACT FROM AUTHOR]

In a laser coherent combination, the phase detection and control is the most critical. Using the beat frequency method, consistence of the phase in output beams can be ensured through real-time detection and correction for the phase change. Phase noises are controlled by a liquid crystal phase modulator. At the same time, the liquid crystal polarization controller is used to make the polarization state stable, which is good for the improvement of the combining efficiency. The wave length of the main oscillation laser is 532 nm. The output power of laser can be adjusted continuously from 0 to 6 W. The shifted frequency of the system is 40 MHz. The accuracy for phase control is superior to λ/70 RMS. In the process of closed-loop control, using the liquid crystal phase and polarization controller, a better signal phase correction of optical path has been achieved for the coherent combination of high power laser arrays. [ABSTRACT FROM AUTHOR]

We present an analytical method for generating ultra-fast pulse sequences. In this approach, the physically intuitive parameters of the sub-pulses-energy, position in time, relative phase, chirp, and the polarization state-can be controlled individually. The pulses are experimentally generated by a pulse shaper which has been recently introduced. It uses three commercial double liquid crystal array modulators to mimic the optimal setup which utilizes four liquid crystal arrays for modulation. A series of double pulses systematically demonstrates the separate and independent control of the sub-pulse parameters. Furthermore, complex multi-pulse sequences are shown. [ABSTRACT FROM AUTHOR]

A model is presented for the effect of a finite extinction ratio of the light modulator used in continuous wave cavity ring-down spectroscopy (CW-CRDS) experiments. We present a simple analytical expression for the minimum isolation required to prevent a significant increase in the fluctuations of the cavity decay rate, which determine the sensitivity of the method. We also present systematic measurements of the signal to noise in CW-CRDS as a function of the effective isolation of the light modulator, and excellent agreement with the model is found. [ABSTRACT FROM AUTHOR]

Tuneable, shaped, ultraviolet (UV) femtosecond laser pulses are produced by shaping and frequency doubling the output of a commercial optical parametric amplifier (OPA). A reflective mode, folded, pulse shaping assembly employing a spatial light modulator (SLM) shapes femtosecond pulses in the visible region of the spectrum. The shaped visible light pulses are frequency doubled to generate phase- and amplitude-shaped, ultrashort light pulses in the deep ultraviolet. This approach benefits from a simple experimental setup and the potential for tuning the central frequency of the shaped ultraviolet waveform. A number of pulse shapes have been synthesised and characterised using cross-correlation frequency resolved optical gating (XFROG). This pulse shaping method can be employed for coherent control experiments in the ultraviolet region of the spectrum where many organic molecules have strong absorption bands. [ABSTRACT FROM AUTHOR]

We demonstrate the spatial homogenization of intense laser pulses by adaptive minimization of spatial chirp of the spectrally broadened output pulses of a filament. A liquid-crystal-based two-dimensional spatial light modulator is used to control the spatial phase of the driver pulse. An evolutionary algorithm finds the optimal spatial laser phase distribution that introduces minimal distortions during filamentation and enhances the beam quality of the output pulse. A homogeneous intensity distribution favours efficient temporal compression close to the bandwidth limit without the need for spatial filtering after the filament. [ABSTRACT FROM AUTHOR]

We introduce a shaper setup which takes advantage of laser pulses passing through a spatial light modulator twice, thereby effectively utilizing a four-liquid crystal mask configuration. This approach grants control not only over the phase and polarization but also the amplitude. The Jones vector of the light wave after passing through the setup is considered in detail including polarization sensitive grating efficiency. A new method of counteracting the polarization dependent grating transmission is described and a comparison between the desired and recorded pulses is presented. [ABSTRACT FROM AUTHOR]

The cross-talk noise in phase encoded holographic memories employing unitary matrices is theoretically investigated. After reviewing some earlier work in this area, we derive a relationship for the noise-to-signal ratio for phase-code multiplexing with unitary matrices. The noise-to-signal ratio rises in a zigzag way on increasing the storage capacity. Cross-talk is mainly caused by high-frequency phase codes. Unitary matrices of even orders have only one bad code, while unitary matrices of odd orders have four bad codes. The signal-to-noise ratios of all other codes can in each case be drastically improved by omission of these bad codes. We summarize the optimal orders of Hadamard and unitary matrices for recording a given number of holograms. The unitary matrices can enable us to adjust the available spatial light modulators to achieve the maximum possible storage capacity in both circumstances with and without bad codes. [ABSTRACT FROM AUTHOR]

By using an elastomer as dielectric medium in a parallel plate capacitor, the attractive forces between the differently charged electrodes strongly compress that layer, representing a special type of electrostrictive effect. With an optical interference technique at the metal-insulator-metal layer system we studied the temporal behaviour of this mechanical deformation. We show that the deformation can be enhanced when the capacitor is laterally structured in order to allow the elastomer volume between the electrodes to move laterally, resulting in typical response times below 1 ms. The elastomer together with the metal electrodes is a metal-insulator-metal optical waveguide, whose mode properties can be tuned by electrically controlled mechanical thickness changes, suggesting applications for low-price electro–optical modulators with response speeds comparable to thermo–optical polymer modulators but with much smaller size. [ABSTRACT FROM AUTHOR]

Our paper deals with temporal shaping of ultrashort pulses by direct spectral filtering performed with bulk acousto-optic filters using noncollinear geometry. This geometry allows arbitrary optical pulse repetition rate and high diffraction efficiency at relatively large optical apertures. A theoretical model of the pulse shaper is presented, emphasizing the degrees of freedom in this shaping technique. Phase and angular dispersion effects are analyzed, and experimental results on generating controllable pulse trains are presented. [ABSTRACT FROM AUTHOR]

A novel actively mode-locked multi-wavelength tunable fiber laser with equally increased or decreased wavelength spacing is presented. It is constructed using a double-ring cavity combined with an amplitude modulator and cascaded fiber Bragg gratings (FBGs). The cavity lengths for all FBGs are intrinsically identical due to the double-ring configuration, and simultaneous mode locking of multiple wavelengths is therefore achieved by applying only one mode-locking signal to the modulator. The FBGs are mounted on a organic plate with angles between adjacent gratings such that the forces applied to the FBGs have an equal force increment; thus, stretching or compressing the cascaded FBGs can achieve a wavelength tuning with equally increased or decreased wavelength spacing. [ABSTRACT FROM AUTHOR]

We report on the application of shaped femtosecond pulses on low-field chirped excitation of an atomic two-level system. The induced transient phenomena can be considered as a phase diagram of the excitation pulse. Their high sensitivity to the phase-modulated pulse is analyzed, by comparing numerical solutions of the time-dependent Schrödinger equation with experimental results. These coherent transients allow for high precision calibration of pulse-shaping setups where usual methods are less efficient. As an illustration, a comparison between 128-pixel and 640-pixel spatial light modulator pulse shapers is given. [ABSTRACT FROM AUTHOR]

We present the application of a novel micro mirror array, which is based on a micro electro mechanical system (MEMS), as one- and two-dimensional phase-modulating spatial light modulator (SLM) for femtosecond pulse shaping in the spectral region from the deep-ultraviolet (DUV) to the near-infrared (NIR) (200-900 nm). Using such a high-resolution MEMS-SLM, we demonstrate one-dimensional pulse shaping at 400 nm, including THz-pulse train generation, chirp compensation, and phase wraps. [ABSTRACT FROM AUTHOR]

Abstract. We report on automated pulse compression of regeneratively amplified femtosecond laser pulses. By employing a feedback-controlled evolutionary algorithm in combination with a femtosecond pulse shaper which is based on a liquid crystal display spatial light modulator, complex phase-modulated laser pulses are optimized, resulting in bandwidth-limited amplified laser pulses. The results obtained are checked in detail by FROG analysis. [ABSTRACT FROM AUTHOR]

We report on experimental results showing a strong wavelength-dependence of cross-talk between photorefractive gratings simultaneously recorded in Bi[sub 12] SiO[sub 20] crystals in the diffusion regime. We find unusually high cross-talk for two gratings with close spatial frequencies at wavelengths 488 and 476 nm. The results indicate that the density of free charge carriers does not directly follow light modulation at low spatial frequencies. [ABSTRACT FROM AUTHOR]

This paper reports on a passively mode-locked and Q-switched Nd:YVO4 laser generating picosecond pulses with an average output power exceeding 7 W. In a first step Q-switch mode-locking was obtained by self Q-switching of a mode-locked oscillator with appropriate cavity design, pump power and output coupling. In a second system the Q-switching was actively controlled and stabilized by modulating the resonator internal losses with an acousto-optic modulator. In the Q-switch mode-locking operation the laser provided 12.8 ps long mode-locked pulses with a repetition rate of 80 MHz. The repetition rate of the Q-switch envelope was 185 kHz. The maximum pulse energy of a single ps pulse was 0.55 μJ which is 5.5 times the pulse energy measured for cw mode locking. The total energy of the pulses within the Q-switch envelope was 42 μJ. [ABSTRACT FROM AUTHOR]

We demonstrate stretch and recompression of a sub-10-fs pulse utilizing a broadband pulse stretcher, a dispersion compensator with a spatial light modulator, and a broadband pulse compressor for ∼10-fs Ti:sapphire chirped-pulse amplification system. Our calculation suggests that the dispersion compensator is useful for dispersion compensation of a Ti:sapphire chirped-pulse amplification system, including multi-pass amplifiers. [ABSTRACT FROM AUTHOR]