Use of Co2+:MgAl2O4 transparent ceramics in passive Q-switching of an Er:Glass laser at 1.534†µm.

We present the implementation of Co2+:MgAl2O4 transparent ceramics as passive Q-switching elements in an Er:Glass laser at 1.534 µm. Linearly polarized pulsed output was obtained by Brewster angle inclination of the material Q-switching plate relative to the laser axis. Separate pulses were ∼105 ns long (FWHM), exhibiting ∼6.2 kW peak power at near TEM00 quality. Several fundamental sample properties important for laser intracavity operation were measured; thermo-optic coefficient dn/dT = ( - 3.8 ± 1) × 10-5 °C-1, thermal lensing factor L-1d(nL)/dT = 2.59 × 10-5 °C-1, linear expansion coefficient α = (3.9 ± 0.6) × 10-5 °C-1, polarizability thermal coefficient ϕ = (7.2 ± 2.2) × 10-5 °C-1, and damage threshold ∼6.5 J/cm2.

Inscribing an output coupler grating directly through the fiber coating with a 266 nm femtosecond laser.

We inscribe with 266 nm femtosecond pulses a ∼0.75% output coupler for a 1550 nm fiber laser directly through the coating of an SMF-28. The output coupler was inscribed with the phase-mask technique without H2 loading. This output coupler was spliced to an active Er/Yb fiber, and a fiber laser with an output power of ∼6.4 W and a slope efficiency of ∼30% was obtained. To the best of our knowledge, this is the first reported attempt to inscribe a fiber Bragg grating through the polymer jacket of an optical fiber with a UV femtosecond laser.

Competing radiative and nonradiative decay of embedded ions states in dielectric crystals: theory, and application to Co2+:AgCl0.5Br0.5.

We present a generally applicable theoretical model describing excited-state decay lifetime analysis of metal ions in a host crystal matrix. In contrast to common practice, we include multi-phonon non-radiative transitions competitively to the radiative one. We have applied our theory to Co2+ ions in a mixed AgCl0.5Br0.5 crystal, and as opposed to a previous analysis, find excellent agreement between theory and experiment over the entire measured temperature range. The fit predicts a zero absolute temperature radiative lifetime τrad(0) = 5.5 ms, more than three times longer than the measured effective low-temperature one τeff(0) = 1.48 ms. Furthermore, the fit configuration potential dissociation energy has been estimated as D = 2500 cm-1 and the lattice vibrational cutoff frequency as hωco = 180 cm-1. We have experimentally verified the latter by optical reflection measurement in the far-IR.

Nonlinear wave interactions between short pulses of different spatio-temporal extents.

We study the nonlinear wave interactions between short pulses of different spatio-temporal extents. Unlike the well-understood mixing of quasi-monochromatic waves, this configuration is highly non-intuitive due to the complex coupling between the spatial and temporal degrees of freedom of the interacting pulses. We illustrate the process intuitively with transitions between different branches of the dispersion curves and interpret it in terms of spectral exchange between the interacting pulses. We verify our interpretation with an example whereby a spectrally-narrow pulse "inherits" the wide spectrum of a pump pulse centered at a different wavelength, using exact numerical simulations, as well as a simplified coupled mode analysis and an asymptotic analytical solution. The latter also provides a simple and intuitive quantitative interpretation. The complex wave mixing process studied here may enable flexible spatio-temporal shaping of short pulses and is the starting point of the study of more complicated systems.

Dual-bandgap hollow-core photonic crystal fibers for third harmonic generation.

We present two novel hybrid photonic structures made of silica that possess two well-separated frequency bandgaps. The addition of interstitial air holes in a precise location and size allows these bandgaps to open with a ratio of ∼3 between their central frequencies at the air line ck(z)/w=1, thus fulfilling the basic guidance condition for third harmonic generation in hollow-core fibers. In addition, these designs may serve for high-power laser delivery of two well-separated wavelengths, such as visible and near infrared.

Phase locking of lasers with self-stabilized minimal coupling.

A novel configuration for phase locking two ring lasers with self-stabilized minimal exchange of power between them is presented. We show experimentally that losses introduced between the lasers are self compensated in order to maintain minimal power exchange between them. The experimental results are in good agreement with numerical results.

Intracavity coherent addition of 16 laser distributions.

The efficient intracavity coherent addition of 16 separate laser Gaussian mode distributions is presented. The coherent addition is achieved in a multichannel pulsed Nd:YAG laser resonator by use of four intracavity interferometric beam combiners. The results reveal 88% combining efficiency with a combined output beam of nearly pure Gaussian distribution.

Intracavity coherent addition of single high-order modes.

We report on efficient intracavity coherent addition of several single high-order mode distributions in a multichannel laser resonator. The phase locking and coherent addition is achieved by using an intracavity interferometric beam combiner. The principle, configuration, and experimental results with pulsed Nd:YAG Laguerre-Gaussian TEM01 and TEM02 laser beam distributions are presented. The results reveal more than 95% combining efficiency with a nearly pure high-order mode output beam distribution in both free-running and Q-switched operation.

Conversion of a high-order mode beam into a nearly Gaussian beam by use of a single interferometric element.

We present a new, compact, and practical optical mode converter that efficiently transforms a high-order Hermite-Gaussian (HG) laser beam into a nearly Gaussian beam. The mode converter is based on coherently adding different transverse parts of the high-order mode beam by use of a single planar interferometric element. The method, configuration, and experimental results obtained with a pulsed Nd:YAG HG TEM10 laser beam are presented. The results reveal that the efficiency of conversion of a HG beam to a nearly Gaussian beam can be as high as 90%.

Efficient formation of a high-quality beam from a pure high-order Hermite-Gaussian mode.

We present a relatively simple method for efficiently transforming a single high-order mode into a nearly Gaussian beam of much higher quality. The method is based on dividing the mode into equal parts that are then combined coherently. We illustrate the method by transforming a Hermite-Gaussian (1, 0) mode with M(x)(2)=3 into a nearly Gaussian beam with M(x)(2)=1. 045 . Experimental results are presented and compared with theoretical results.