Randall J. Knize

Graphene mode locked, wavelength-tunable, dissipative soliton fiber laser

Atomic layer graphene possesses wavelength-insensitive ultrafast saturable absorption, which can be exploited as a “full-band” mode locker. Taking advantage of the wide band saturable absorption of the graphene, we demonstrate experimentally that wide range (1570–1600 nm) continuous wavelength tunable dissipative solitons could be formed in an erbium doped fiber laser mode locked with few layer graphene.

Mode locking of ceramic Nd:yttrium aluminum garnet with graphene as a saturable absorber

The mode-locking of a ceramic Nd:yttrium aluminum garnet (YAG) solid-state laser (SSL) with solution processed graphene as saturable absorber (SA) was demonstrated. Transform-limited pulses with duration of 4 ps centered at 1064 nm were generated for a nondispersion compensated Nd:YAG SSL. Z-scan studies revealed that the graphene SA has a saturation intensity of 0.87 M W cm−2 and a normalized modulation depth of 17.4%. Our results illustrate the potential of using graphene as a mode locker for SSLs.

Review of alkali laser research and development

Abstract. In this review we present an analysis of optically pumped alkali laser research and development from the first proposal in 1958 by Schawlow and Townes to the current state. In spite of the long history, real interest in alkali vapor lasers has appeared in the past decade, after the demonstration of really efficient lasing in Rb and Cs vapors in 2003 and the first successful power scaling experiments. This interest was stimulated by the possibility of using efficient diode lasers for optical pumping of the alkali lasers and by the fact that these lasers can produce a high quality and high power output beam from a single aperture. We present a review of the most important achievements in high power alkali laser research and development, discuss some problems existing in this field, and provide future perspectives in diode pumped alkali laser development.

Linear optical effects in Z-scan measurements of thin films

We show that it is possible, in Z-scan measurements ofthin films, to obtain data that closely resemble typical results for nonlinear optical materials, but which actually arise from linear optical effects caused by sample damage. Z-scan measurements on a silica-based thin film yielded the expected peak-valley signature of Z-scan data, but subsequent analysis and microscopic examination of the film indicated that the data resulted from an ablation hole produced in the film when it was near the laser focus. The resulting spatial variation of the linear refractive index of the film produced a lensing effect that mimicked the typical Z-scan response. Scalar diffraction theory was used to model the effects of a spatially varying refractive index and gave results that qualitatively agreed with the Z-scanmeasurements.

Efficient potassium diode pumped alkali laser operating in pulsed mode.

This paper presents the results of our experiments on the development of an efficient hydrocarbon free diode pumped alkali laser based on potassium vapor buffered by He gas at 600 Torr. A slope efficiency of more than 50% was demonstrated with a total optical conversion efficiency of 30%. This result was achieved by using a narrowband diode laser stack as the pump source. The stack was operated in pulsed mode to avoid limiting thermal effects and ionization.

Modeling of pulsed K diode pumped alkali laser: Analysis of the experimental results

A simple optical model of K DPAL, where Gaussian spatial shapes of the pump and laser intensities in any cross section of the beams are assumed, is reported. The model, applied to the recently reported highly efficient static, pulsed K DPAL [Zhdanov et al, Optics Express 22, 17266 (2014)], shows good agreement between the calculated and measured dependence of the laser power on the incident pump power. In particular, the model reproduces the observed threshold pump power, 22 W (corresponding to pump intensity of 4 kW/cm2), which is much higher than that predicted by the standard semi-analytical models of the DPAL. The reason for the large values of the threshold power is that the volume occupied by the excited K atoms contributing to the spontaneous emission is much larger than the volumes of the pump and laser beams in the laser cell, resulting in very large energy losses due to the spontaneous emission. To reduce the adverse effect of the high threshold power, high pump power is needed, and therefore gas flow with high gas velocity to avoid heating the gas has to be applied. Thus, for obtaining high power, highly efficient K DPAL, subsonic or supersonic flowing-gas device is needed.

Demonstration of a diode pumped continuous wave potassium laser

This paper presents a first demonstration of a diode pumped Potassium laser. Two narrowband laser diode arrays with a linewidth about 10 GHz operating at 766.7 nm were used to pump Potassium vapor buffered by Helium gas at 600 torr. A stable laser cavity with longitudinal pumping and orthogonal polarizations of the pump and laser beams was used in this experiment. A slope efficiency about 25% was obtained.

Degenerate four-wave mixing in two-level saturable absorbers

A calculation of degenerate four-wave mixing in a homogeneously broadened two-level saturable absorber is presented. An analytical formula for the local electric dipole polarization responsible for degenerate four-wave mixing is derived for arbitrary electric-field strengths. The overall efficiency of the medium is calculated by numerically solving the coupled wave equations with the use of the phase-matching electric dipole polarization. Solutions are presented when the laser is tuned on and off resonance for various input laser intensities and linear absorption coefficients. Optimal conditions for maximum efficiency are discussed.

Holographically corrected telescope for high-bandwidth optical communications

We present a design for an optical data communications receiver-transmitter pair based on the holographic correction of a large diameter, poor-quality, reflecting primary mirror. The telescope has a narrow bandwidth (<0.1 nm) with good signal frequency isolation (>60 dB) and is scalable to meter-class apertures. We demonstrate the correction of a reflector telescope with over 2000 waves of aberration to diffraction-limited operation, capable of handling data transmission rates up to 100 GHz.

Experimental study of the Cs diode pumped alkali laser operation with different buffer gases

Abstract. Cs diode pumped alkali laser (DPAL) operation using ethane, methane, and mixtures of these hydrocarbons with the noble gases He and Ar as a buffer gas for spin–orbit relaxation was studied in this work. The best Cs DPAL performance in continuous wave operation with flowing gain medium was achieved using pure methane, pure ethane, or a mixture of ethane (minimum of 200 Torr) and He with a total buffer gas pressure of 300 Torr.