Order Laguerre-Gaussian Mode Research Articles

Excitation of Mode Groups in Multimode Fibers With the Aid of Diffractive Optics

In this letter, we report on the excitation of low order Laguerre–Gaussian mode groups with a common propagation constant in a multimode gradient index optical fiber. Enabling generic space-division multiplexer was based on a key multichannel diffractive optical element. The experimental results show integrity of the excited mode groups in an OM2 multimode fiber optic patch cord.

Actively Q-switched and vortex Nd:YAG laser

We reported an efficient and actively Q-switched Nd:YAG laser that emitted the first order Laguerre–Gaussian mode with right-handedness helical wavefront. In the experiment, the pump light was converted into annular profile through off-focus coupling in a conventional multi-mode fiber. The laser cavity, consisting of a laser crystal and an output coupler and incorporating an acousto-optic Q switch and an etalon, was simple and compact. The Q-switched performance of the laser was given in detail.

Q-switched Nd:YAG optical vortex lasers

Q-switched operation of a high-quality Nd:YAG optical vortex laser with the first order Laguerre-Gaussian mode and well-determined helical wavefronts using a fiber-based pump beam conditioning scheme is reported. A simple two-mirror resonator incorporating an acousto-optic Q-switch was employed, along with an etalon and a Brewster plate to enforce the particular helicity of the output. The laser yielded Q-switched pulses with ~250 μJ pulse energy and ~33 ns pulse duration (FWHM) at a 0.1 kHz repetition rate for 5.1 W of absorbed pump power. The handedness of the helical wavefronts was preserved regardless of the repetition rates. The prospects of further power scaling and improved laser performance are discussed.

Very high-order pure Laguerre-Gaussian mode selection in a passive Q-switched Nd:YAG laser

An intra-cavity phase element, combined with a passive Q-switch saturable absorber and a suitable intra-cavity aperture, can provide extremely high mode discrimination, so as to obtain laser operation with single, pure, very high order Laguerre-Gaussian mode. With a Nd:YAG laser setup, well controlled and extremely stable Q-switched operation in the degenerate Laguerre-Gaussian TEM04, TEM14, TEM24, TEM34, and TEM44 modes was obtained. The measured output energy per pulse for each of these modes was 5.2mJ, 7.5mJ, 10mJ, 12.5mJ, and 13.7mJ respectively, compared to 2.5mJ for the Gaussian mode without the phase element (more than a five fold increase in output energy). Correcting the phase for these modes, so that all transverse lobes have uniform phase, results in a very bright and narrow central lobe in the far field intensity distribution that can theoretically contain more than 90% of the output energy.

Transverse modes in oxide confined VCSELs: Influence of pump profile, spatial hole burning, and thermal effects

We present experimental studies on the transverse mode emission behaviour of oxide-confined Vertical Cavity Surface Emitting Lasers (VCSELs). VCSELs with aperture diameters of 6um and 11um exhibit a wide variety of emission patterns from low order Hermite- Gaussian modes to high order Laguerre-Gaussian modes. We obtain detailed information about the spatial gain distribution by recording spontaneous emission intensity profiles during lasing operation. We conclude from these profiles, that the spatial carrier distribution is primarily governed by the in uence of pump induced current spreading and is only secondarily in uenced by further effects such as spatial hole burning, and thermal gradients in the laser. The combination of these mechanisms causes a strong tendency towards the emission of high order transverse modes.