super-Gaussian Mode Research Articles

Comparison of Gaussian and super Gaussian laser beams for addressing atomic qubits

We study the fidelity of single qubit quantum gates performed with two-frequency laser fields that have a Gaussian or super Gaussian spatial mode. Numerical simulations are used to account for imperfections arising from atomic motion in an optical trap, spatially varying Stark shifts of the trapping and control beams, and transverse and axial misalignment of the control beams. Numerical results that account for the three dimensional distribution of control light show that a super Gaussian mode with intensity $I\sim e^{-2(r/w_0)^n}$ provides reduced sensitivity to atomic motion and beam misalignment. Choosing a super Gaussian with $n=6$ the decay time of finite temperature Rabi oscillations can be increased by a factor of 60 compared to an $n=2$ Gaussian beam, while reducing crosstalk to neighboring qubit sites.

Generation of custom modes in a Nd:YAG laser with a semipassive bimorph adaptive mirror

Custom modes at a wavelength of 1064 nm were generated with a deformable mirror. The required surface deformations of the adaptive mirror were calculated with the Collins integral written in a matrix formalism. The appropriate size and shape of the actuators as well as the needed stroke were determined to ensure that the surface of the controllable mirror matches the phase front of the custom modes. A semipassive bimorph adaptive mirror with five concentric ring-shaped actuators and one defocus actuator was manufactured and characterised. The surface deformation was modelled with the response functions of the adaptive mirror in terms of an expansion with Zernike polynomials. In the experiments the Nd:YAG laser crystal was quasi-CW pumped to avoid thermally induced distortions of the phase front. The adaptive mirror allows to switch between a super-Gaussian mode, a doughnut mode, a Hermite-Gaussian fundamental beam, multi-mode operation or no oscillation in real time during laser operation.

Numerical simulation of a high-average-power diode-pumped ytterbium-doped YAG laser with an unstable cavity and a super-Gaussian mirror

A numerical technique with which to compute the output characteristics of a solid-state laser with an unstable cavity and a super-Gaussian coupling mirror is proposed. This technique is applied to an Yb:YAG actively Q-switched laser. With this formalism, the mode formation for the fundamental mode is analyzed and the performance achievable by such a laser for various cavity parameters is determined. Then the results obtained with such a cavity are compared with those given for a stable cavity with graded phase output mirror that is also used for obtaining super-Gaussian mode.

Thermo-optically driven adaptive mirror for laser applications

An adaptive mirror is investigated that is based on the deformation of the reflective surface due to thermal expansion of an underlying material that can be locally heated with an external light source. The mirror is made from a glass plate coated with a 1-mm-thick layer of a material with a large thermal expansion coefficient that was finally sputter coated with a thin gold film. The adaptive mirror is thermo-optically heated with an incandescent lamp. To generate the desired temperature pattern an aperture mask is used. The deformation of the adaptive mirror is measured with a Michelson interferometer. It is shown that the spatial resolution and amplitude of the deformation are sufficient for the application as an adaptive mirror. As a possible application the suitability of this mirror type as part of a laser resonator to generate a super-Gaussian mode is discussed.

Generation of Super-Gaussian modes in Nd:YAG lasers with a graded-phase mirror

A dielectric graded-phase mirror was developed to change the intensity distribution of the fundamental mode in an Nd:YAG laser resonator to a top-hat profile. A super-Gaussian mode of the sixth order was generated by means of a graded-phase mirror with a simple ring-shaped phase step on a spherical reflector. The depth of the ring on the mirror was 90 nm. The graded-phase mirror was manufactured with an ordinary vapor deposition technique using an appropriate mask. Laser experiments with CW and repetitively pulsed diode-laser pumping were performed and compared. Slope efficiencies up to 19% were achieved. The experimental results are in excellent agreement with the theory.

Diffractive optical elements for intra-cavity beam-shaping of laser modes

Diffractive optical elements (DOE) are applied as intra-cavity mode selection devices for customizing the fundamental mode of laser resonators for high power laser systems. Using a phase-conjugating mode selecting element (MSE) in a laser oscillator, we are able to produce a good approximation to a super-Gaussian mode with a near flat intensity profile. This offers higher energy extraction from any following laser amplifiers compared to an unmodified Gaussian TEM00 mode. Two different designs for operation in a 1 m cavity length Nd:YAG master oscillator are presented. Both designs are surface relief phase elements fabricated in fused silica using photolithography with reactive-ion etching to produce 16 level elements for use in transmission. One element is designed to replace the cavity end mirror, while the other stands off an arbitrary distance from the end mirror. A novel iterated design for these transmissive elements is introduced. Numerical results and experimental measurements are presented and discussed.