Wavefront Of Laser Beam Research Articles

Algorithms for the reconstruction of the singular wave front of laser radiation: analysis and improvement of accuracy

The possibility of reconstructing a singular wave front of laser beams by the local tilts of the wave front measured with a Hartmann sensor is considered. The accuracy of the reconstruction algorithm described by Fried is estimated and its modification is proposed, which allows one to improve the reliability of the phase reconstruction. Based on the Fried algorithm and its modification, a combined algorithm is constructed whose advantages are demonstrated in numerical experiments.

Laser beam wavefront correction for ultra high intensities with the 200 TW laser system at the advanced laser light source

We successfully implemented laser beam wavefront correction on the 200 TW laser system at the Advanced Laser Light Source. Ultra high intensities in excess of 10(20) W/cm(2) have been demonstrated. This system is, to our knowledge, the first 100 TW class laser to combine simultaneously ultra high intensity, 10(9) laser pulse contrast ratio and 10 Hz high repetition rate.

Highly sensitive wave-front sensor with a non-zero-order phase plate

We propose a novel highly sensitive wave front detection method for a quick check of a flat wave front by taking advantage of a non-zero-order pi phase plate that yields a non-zero-order diffraction pattern. When a light beam with a flat wave front illuminates a phase plate, the zero-order intensity is zero. When there is a slight distortion of the wave front, the zero-order intensity increases. The ratio of first-order intensity to that of zero-order intensity is used as the criterion with which to judge whether the wave front under test is flat, eliminating the influence of background light. Experimental results demonstrate that this method is efficient, robust, and cost-effective and should be highly interesting for a quick check of a flat wave front of a large-aperture laser beam and adaptive optical systems.

Measurement of the wavefront of a laser diode system for intersatellite communication by a Jamin double-shearing interferometer

The frame of a laser diode transmitter for intersatellite communication is concisely introduced. A simple, novel and visual method for measuring the diffraction-limited wavefront of the transmitter by a Jamin double-shearing interferometer is proposed. To verify the validity of the measurement, the far-field divergence of beam is additionally rigorously analysed in terms of the Fraunhofer diffraction. The measurement, the necessary analyses and discussion are given in detail. By directly measuring the fringe widths and quantitatively interpreting the interference fringes, the minimum detectable wavefront height (DWH) of the wavefront is only 0.2 gimel (the distance between the perfect plane wavefront and the actual wavefront at the transmitting aperture) and the corresponding divergence is only 65.84 mu rad. This indicates that the wavefront approaches the diffraction-limited condition. The results show that this interferometer is a powerful tool for testing the semiconductor laser beam's wavefront, especially the diffraction-limited wavefront.

Transmission-type position sensor for the straightness measurement of a large structure

A new position sensor has been fabricated which is suitable for detecting the accurate straightness reference of a laser beam. This is achieved by fabricating a four-cell type photodiode inside a Si micro-mesh structure. This sensor does not disturb the direction or the wave front of the reference laser beam as it absorbs only some of the incident photons and transmits the rest down stream. The straightness of ~1 m structures can be measured with ~1 µm accuracy at many points by placing the sensors in series.

Acoustic stabilization of the wavefront of a laser beam in a nonuniform gaseous medium

The action of an acoustic field on a nonisothermal gaseous medium for the purpose of improving the optical characteristics of the medium is studied. Restoration of optical uniformity of the gas and stabilization of the wavefront of a laser beam were modelled in experiments with acoustic flows.

Efficient power coupling from a 980-nm, broad-area laser to a single-mode fiber using a wedge-shaped fiber endface

A theoretical and experimental study of an efficient technique for coupling a broad-area laser to a single-mode fiber without the use of bulk optical components was carried out. The technique uses a wedge-shaped fiber endface to approximate a cylindrical lens action to correct for the phase mismatch between the curved laser beam wavefront and the planar fiber beam. A theoretical formula for the coupling efficiency in the absence of both angular and transverse misalignments is derived. By optimizing the wedge angle and the axial separation between the laser facet and the fiber endface, a maximum coupling efficiency of 47%, compared to 20% for the square endface, achieved, resulting in 15.2 mW of power in the single-mode fiber. The fabrication process consists of a simple polishing procedure requiring a wedge-shaped polishing tool and is highly reproducible.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Photothermal lens aberration effects in two laser thermal lens spectrophotometry

A comparison of theories describing two laser photothermal lens signals is given. The aberrant nature of this lens is accounted for in a theory which treats the propagation of a monitor laser in terms of a phase shift in this laser beam wave front. The difference between theories are discussed in terms of the predicted signal strengths and temporal behavior. The aberrant theory results in smaller theoretical signal strengths and different functional relationships between signal and analyte level.

Acoustooptic 2-D profile shaping of a Gaussian laser beam

Acoustooptic 2-D profile shaping of a Gaussian laser beam has been achieved by two plane ultrasonic waves progressing in orthogonal directions. The spot size W of the Gaussian laser beam must be considerable less than the wavelength lambda of the ultrasonic wave at the acoustooptic interaction region. The ultrasonic cell is dealt with as a Raman-Nath 2-D phase grating but serves as a 2-D beam deflector in time for the interaction scheme of interest. The wave front of the Gaussian laser beam must be almost plane in the interaction region. The profile shaping condition is 0.15 < or = (W/lambda) < or = 0.30 only when the Raman-Nath parameter dependent on the ultrasonic power has values between v = 1.0 and 2.0.

Adequacy of a theoretical model in the solution of the inverse problem of the statistics of laser breakdown

An analysis is made of the possible reasons for the inadequacy of a theoretical model used to solve the inverse problem in the statistics of laser breakdown, i.e., the model employed to find the characteristics of microdefects in a given material from the statistical relationships governing laser breakdown. Some tests for checking the agreement between the model and the experimental situation are discussed. Attention is drawn to the existence of two different approaches to a statistical description of laser damage and the conditions are found under which the results of the two approaches are in agreement. A detailed analysis is made of the consequences of distortions of a laser beam wavefront. A description is given of a method for estimating the real optical strength of a material from the nature of the size dependence of laser breakdown.

Laser beam wavefront diagnostics by a three-plate ring interferometer and a grating spatial filter system

A three-plate identical ring interferometer is a white-light interferometer with constant lateral translation shearing, and its precision of measurement corresponds to the depth of focus. The grating spatial filter system directly gives the information of the distortion quantity in the wavefront, and is also applicable to diagnostics of small-aperture light beams.

Measurement of phase fluctuations in a HF chemical laser beam

A new phase detector, which uses an acousto-optic modulation and optical heterodyne technique, has been developed. The minimum detectable phase difference is 4 °, with a temporal response of 10 μsec and a spatial resolution of 0.14 mm. This phase detector was used to measure fluctuations in the wave front of a cw HF chemical laser beam caused by mechanical vibration, medium turbulence, and gain variation. Potential applications are laser beam quality measurement, beam steering measurement, and sensing for an active resonator.

Optimization Procedures for Digital Light Beam Deflectors

The geometrical dimensions for optimum performance of digital deflectors are derived for various configurations and modes of operation. These calculations show the capacity-speed product (CSP) commonly used as a figure of merit in the evaluation of the performance of digital deflectors to be applicable only for the condition of minimum power consumption of the last deflection stage. For minimum drive voltage the CSP should be replaced by a capacity factor, and other than the commonly considered alternating stage configuration should be used. It is furthermore pointed out that beyond such figures of merit other physical parameters play an important role in the implementation of practical deflection systems, for example, in a twenty-stage system the optical inhomogeneities in each deflection stage should not distort the transmitted laser beam wavefront by more than lambda/100 per stage for a signal-to-noise ratio of 20.

Effect of Gaussian Beam Spread on Phase Velocity Matching in cw Optical Second-Harmonic Generation

This paper reports the results of an experimental and theoretical study of the angular variation of optical second-harmonic generation in ammonium dihydrogen phosphate using a Gaussian single-transverse-mode cw gas-laser beam. The observed angular dependence of the second-harmonic output near the phase matching angle is significantly different from the ${[\frac{(sin\ensuremath{\psi})}{\ensuremath{\psi}}]}^{2}$ angular dependence predicted by plane-wave theory. The difference can be quantitatively explained by an extended analysis which takes into account the Gaussian amplitude distribution and spherical wavefront of the cw laser beam. The theory predicts small but significant corrections to the results of measurements of the nonlinear coefficients of materials. These corrections can also account, at least approximately, for the effects of small crystal defects and imperfectly Gaussian beam patterns.