Jason Zweiback

Alkali-vapor lasers

We report on the results from several of our alkali laser systems. We show highly efficient performance from an alexandrite-pumped rubidium laser. Using a laser diode stack as a pump source, we demonstrate up to 145 W of average power from a CW system. We present a design for a transversely pumped demonstration system that will show all of the required laser physics for a high power system.

28W average power hydrocarbon-free rubidium diode pumped alkali laser

We present experimental results for a high-power diode pumped hydrocarbon-free rubidium laser with a scalable architecture. The laser consists of a liquid cooled, copper waveguide which serves to both guide the pump light and to provide a thermally conductive surface near the gain volume to remove heat. A laser diode stack, with a linewidth narrowed to approximately 0.35 nm with volume bragg gratings, is used to pump the cell. We have achieved 24W average power output using 4 atmospheres of naturally occurring helium ((4)He) as the buffer gas and 28W using 2.8 atmospheres of (3)He.

High-channel-count fiber Bragg gratings fabricated by phase-only sampling

In conclusion, it has been demonstrated that phase-only sampling can generate high-channel count fibre Bragg gratings (FBGs) with the conventional technique of side writing through a phase mask. Additional phase-only sampling schemes and experiment results will be discussed.

Split of phase shifts in a phase mask for fiber Bragg gratings

Using rigorous finite-difference in time-domain analysis for near field diffraction of a phase-shifted phase mask, we discover that the phase shift is not replicated in the fiber by side-writing through the mask, but is split into two half-magnitude phase shifts with a separation proportional to the fiber-to-phase mask spacing. We show by a physical model for cumulated phase that spectral asymmetry observed in a multichannel fiber Bragg grating (FBG) with a binary phase Dammann sampling function is caused by this split. We propose a new binary phase-only sampling design, which precompensates the phase-shift splitting effect and produces high channel count FBGs without asymmetry in the channel spectrum.

Phase-only sampled 45 channel fiber Bragg grating written with a diffraction-compensated phase mask

A novel phase-only sampled 45 channel fiber Bragg grating (channel spacing, 100 GHz) with high interchannel and intrachannel reflection uniformity and precise dispersion matching capability to an 80 km SMF-28 fiber is demonstrated. This grating is fabricated by the side-writing technique, in which phase information of continuous phase-only sampling is completely incorporated into a diffraction-compensated phase mask.

High-energy transversely pumped alkali vapor laser

We report on the results from our transversely pumped alkali laser. This system uses an Alexandrite laser to pump a stainless steel laser head. The system uses methane and helium as buffer gasses. Using rubidium, the system produced up to 40 mJ of output energy when pumped with 63 mJ. Slope efficiency was 75%. Using potassium as the lasing species the system produced 32 mJ and a 53% slope efficiency.

Modeling laser performance of scalable side pumped alkali laser

Diode pumped alkali lasers (DPAL) offer the potential for high power and efficient operation. The extremely low quantum defect of the alkali system minimizes thermal management requirements. At the same time DPALs keep advantages of gas lasers (no thermal stresses, high intrinsic beam quality). Side pumped geometry simplifies system design, separating laser and pump light and providing physical space for a large number of diode stacks needed for power scaling. The three-level nature of these lasers complicates modeling, making numerical simulation the most viable option for system studies in this geometry. We have built a simplified numerical code for simulation of CW laser performance in different side pumped geometries and studied performance of a rubidium DPAL with helium and methane buffer gases at high pump power. We observed dramatic differences in pump absorption with the laser turned off compared to an operating laser. Cell temperature is a key parameter that controls effective absorption length. If pump density is sufficiently high, we can find an operating point with optical to optical efficiency above 60% with reasonably homogenous spatial laser output profile even for a single side pumped laser cell.

Diode pumped alkali vapor lasers for high power applications

General Atomics has been engaged in the development of diode pumped alkali vapor lasers. We have been examining the design space looking for designs that are both efficient and easily scalable to high powers. Computationally, we have looked at the effect of pump bandwidth on laser performance. We have also looked at different lasing species. We have used an alexandrite laser to study the relative merits of different designs. We report on the results of our experimental and computational studies.

Diffraction Compensation of Masks for High Channel-CountPhase-Only Sampled Fiber Bragg Gratings

Full C-band phase-only sampled gratings are fabricated using the standard proximity side-writing technique. The mask is designed by a simple and novel method that compensates for very significant diffraction effects from the mask to the fiber core.