General design principle for structured light lasers.

Using custom laser cavities to produce as the output some desired structured light field has seen tremendous advances lately, but there is no universal approach to designing such cavities for arbitrarily defined field structures within the cavity, e.g., at both the output and gain ends.

Extended focus depth for Gaussian beam using binary phase diffractive optical elements.

A novel technique to improve the focus depth of a Gaussian beam is presented in this paper. The improvement is based on two-step beam shaping using a cascade of binary phase diffractive optical elements (BPDOEs). The first BPDOE transforms the incident Gaussian beam into a high-order radial Laguerre-Gaussian beam (LG).

Generation of Laguerre-Gaussian LGp0 beams using binary phase diffractive optical elements.

In recent years, considerable attention has been devoted to laser beams with specific intensity profile, i.e., non-Gaussian.

Reconstruction-free sensitive wavefront sensor based on continuous position sensitive detectors.

We propose a new device that is able to perform highly sensitive wavefront measurements based on the use of continuous position sensitive detectors and without resorting to any reconstruction process. We demonstrate experimentally its ability to measure small wavefront distortions through the characterization of pump-induced refractive index changes in laser material. In addition, it is shown using computer-generated holograms that this device can detect phase discontinuities as well as improve the quality of sharp phase variations measurements.

Doughnut laser beam as an incoherent superposition of two petal beams.

Laguerre-Gaussian beams with a nonzero azimuthal index are known to carry orbital angular momentum (OAM), and are routinely created external to laser cavities. The few reports of obtaining such beams from laser cavities suffer from inconclusive evidence of the real electromagnetic field. In this Letter we revisit this question and show that an observed doughnut beam from a laser cavity may not be a pure Laguerre-Gaussian azimuthal mode but can be an incoherent sum of petal modes, which do not carry OAM.

Tuneable Gaussian to flat-top resonator by amplitude beam shaping.

We outline a simple laser cavity comprising an opaque ring and a circular aperture that is capable of producing spatially tuneable laser modes, from a Gaussian beam to a Flat-top beam. The tuneability is achieved by varying the diameter of the aperture and thus requires no realignment of the cavity. We demonstrate this principle using a digital laser with an intra-cavity spatial light modulator, and confirm the predicted properties of the resonator experimentally.

Spatial properties of coaxial superposition of two coherent Gaussian beams.

In this paper, we explore theoretically and experimentally the laser beam shaping ability resulting from the coaxial superposition of two coherent Gaussian beams (GBs). This technique is classified under interferometric laser beam shaping techniques contrasting with the usual ones based on diffraction. The experimental setup does not involve the use of some two-wave interferometer but uses a spatial light modulator for the generation of the necessary interference term.

Exciting higher-order radial Laguerre-Gaussian modes in a diode-pumped solid-state laser resonator.

In this paper we experimentally demonstrate the intracavity generation of selected Laguerre-Gaussian modes of variable radial order, from 0 to 5. Our technique requires only an amplitude mask made up of absorbing rings to be placed inside the cavity, with the ring radii selected to coincide with the zeros of the desired Laguerre-Gaussian mode. We demonstrate high mode purity and a mode volume proportional to the order of the mode.

Transverse superresolution technique involving rectified Laguerre-Gaussian LG(p)⁰ beams.

A promising technique has been proposed recently [Opt. Commun. 284, 1331 (2011), Opt.

Baryscan: a sensitive and user-friendly alternative to Z scan for weak nonlinearities measurements.

A new and efficient technique for measuring weak optical nonlinearities is reported. Like Z scan, its implementation is basic, both experimentally and theoretically, but leads to an improved sensitivity of λ/5.10⁴, which represents, to date, one of the highest observed enhancements.

Variant of the method of Fox and Li dedicated to intracavity laser beam shaping.

We present a variant of the method of Fox and Li [Bell Syst. Tech. J.

Properties of a laser cavity containing an absorbing ring.

This paper considers the transverse optical properties of an absorbing ring when it is lighted by a symmetrical Laguerre-Gauss beam TEM(p0). It is demonstrated that the insertion of an opaque ring having adequate size inside a diaphragmed laser cavity is able to improve greatly (rate of about 100%) the discrimination between the TEM(00) and the TEM(10) modes, while keeping the diffraction losses unchanged or even decreased.

Cascades of pi-phase plates: a transparent diffractive focusing system.

Typically, refractive lenses are used to focus rays of light, but an alternative way can be found by exploiting diffraction of light. It is well known that cascades of hard-edge apertures are able to focus light but with the great drawback of absorption losses. In this paper, we demonstrate that replacing hard-edge apertures with pi-phase plates within a cascade greatly improves the focusing of collimated Gaussian beams.

Modeling the propagation of apertured high-order Laguerre-Gaussian beams by a user-friendly version of the mode expansion method.

The mode expansion method (MEM) models the propagation of an apertured beam by expressing the diffracted field as a finite series of Laguerre-Gaussian or Hermite-Gaussian modes. An optimal expansion parameter set (beam waist of the modes and its location) reduces the number of modes, which is difficult to derive, especially for high-order incident beams. We propose a user-friendly version of the MEM in which the expansion parameter set and the suitable number of modes are simply deduced from the approximation of the apertured incident beam.

Adaptive Laguerre-Gaussian variant of the Gaussian beam expansion method.

A variant of the Gaussian beam expansion method consists in expanding the Bessel function J0 appearing in the Fresnel-Kirchhoff integral into a finite sum of complex Gaussian functions to derive an analytical expression for a Laguerre-Gaussian beam diffracted through a hard-edge aperture. However, the validity range of the approximation depends on the number of expansion coefficients that are obtained by optimization-computation directly. We propose another solution consisting in expanding J0 onto a set of collimated Laguerre-Gaussian functions whose waist depends on their number and then, depending on its argument, predicting the suitable number of expansion functions to calculate the integral recursively.

Digital phase contrast with the fractional Fourier transform.

A new method of digital phase contrast based on fractional-order Fourier reconstruction is proposed. We show that the diffraction patterns produced by pure phase objects exhibit linear chirp functions that can be advantageously processed using the fractional Fourier transform. The optimal fractional orders lead to the longitudinal location of the phase object, while the analysis of the reconstructed pattern leads to its diameter and to the value of the phase shift.

Beam-shaping longitudinal range of a binary diffractive optical element.

An experimental and theoretical investigation of laser beam shaping using a simple binary diffractive optic is presented. Beam tailoring has been characterized by the experimental determination of two relevant parameters: beam propagation factor M(2) and the beam-shaping longitudinal range, which represents the propagating distance for which the tailored beam remains nearly unchanged.

Simple interferometric technique for generation of a radially polarized light beam.

We present a theoretical and experimental investigation of an interferometric technique for converting a linearly polarized Gaussian beam into a radially polarized doughnut beam. The experimental setup accomplishes the coherent summation of two orthogonally polarized TEM01 and TEM10 beams that are obtained from the transformation of a TEM00 beam by use of a simple binary diffractive optical element. We have shown that the degree of radial polarization is maximum at a given distance from the interferometer output port that depends on the diameter of the incident beam at the interferometer input port.

Improvement of the self-Q-switching behavior of a Cr:LiSrAlF6 laser by use of binary diffractive optics.

It has been shown experimentally and theoretically that Q-switching behavior is possible in a flashlamp-pumped Cr-doped LiSrAlF6 (Cr3+:LiSAF) laser that consists only of two mirrors, a laser crystal, and a diaphragm. We demonstrate that insertion into a laser of a binary diffractive optical element can speed up the dynamics of the self-Q-switched laser such that the output pulse is shortened (from 60 to 33 ns) and its energy is increased (from 36 to 54 mJ). The self-Q-switching behavior of the laser has the ability to produce a laser pulse with a duration that one can adjust continuously from 60 to 700 ns just by opening the diaphragm.