A new 100μm aperture, 920nm laser diode chip was developed to improve fiber coupling efficiency and reliability. These chips have been assembled into single-emitter and multi-emitter packages with 105μm diameter fiber-coupled output. The single-emitter package is rated for 12W operation, while the multi-emitter package is rated at 140W. Power conversion efficiency is 50%. Over one year of accelerated active life testing has been completed along with a suite of passive, environmental qualification tests. These pumps have been integrated into 2kW, 4kW, and 6kW fiber laser engines that demonstrate excellent brightness, efficiency, and sheet metal cutting quality and speed.
We report the development of fused-fiber pump and signal combiners. These combiners are enabling components of a ytterbium fiber-laser emitting 4 kW of 1080-nm radiation. The fiber-laser system consists of seven fiber laser modules and a 7:1 signal combiner. The laser modules are end-pumped by 90 915-nm JDSU L4 diode-lasers, yielding a nominal pump power of 900 W. The diode laser radiation is coupled into the laser fiber through a 91:1 fused-fiber pump combiner. The input fibers of this pump combiner are standard 105/125-um multimode fibers with an NA of 0.22. These fibers form a hexagonally packed fused-fiber bundle, which is tapered to match the cladding diameter of the laser fiber. Eighty-six percent of the light exiting the pump-combiner is emitted within an NA of 0.32, and all measurable power is emitted within an NA of 0.45. The typical insertion loss of the pump combiners is <1%. The high-brightness radiation of seven laser modules is combined into a single output fiber using a 7:1 fused-fiber signal combiner providing a total power of >4 kW in the single output beam. The beam parameter product of the combined output was 2.5 mm-mrad. The low insertion loss of < 2% indicates that the signal combiner is suitable to handle even higher laser powers.
We have developed a commercial 4-kW fiber laser consisting of seven, 600-W modules whose outputs are combined
with a fused-fiber combiner. The system architecture has several practical advantages, including pumping with reliable
single-emitter diodes, monolithic fused-fiber construction (no free-space beams), and end pumping using a 91:1 pump
combiner (eliminating the need for complex pump/signal combiners). Typical results at 4-kW output power are a beamparameter
product of 2.6 mm-mrad, 8-hr power stability of < 0.5% rms, central wavelength of 1080 nm, and linewidth of
1.2 nm FWHM. These lasers have been incorporated into Amada machines used for cutting metal sheet and plate and
have been used to cut aluminum, mild steel, stainless steel, brass, titanium, and copper with a thickness up to 19 mm. A
world-record cutting speed of 62 m/min has been demonstrated for 1-mm aluminum sheet metal.
Results for a new compact 488 nm solid-state laser for biomedical applications are presented. The architecture is based
on a multi-longitudinal mode external cavity semiconductor laser with frequency doubling in a ridge waveguide fabricated in periodically poled MgO:LiNbO<sub>3</sub>. The diode and the waveguide packaging have been leveraged from telecom packaging technologies. This design enables built-in control electronics, low power consumption (≤ 2.5 W) and a footprint as small as 12.5 x 7 cm. Due to its fiber-based architecture, the laser has excellent beam quality, M<sup>2</sup> <1.1. The laser is designed to enable two light delivery options: free-space and true fiber delivered output. Multi-longitudinal
mode operation and external doubling provide several advantages like low noise, internal modulation over a broad frequency range and variable output power. Current designs provide an output power of 20 mW, but laser has potential for higher power output.
We report a simple and compact all-solid-state laser generating 488 nm light with continuously variable output power in the range from 1 mW to over 120 mW. We frequency double single frequency radiation from an external cavity semiconductor laser in a periodically poled MgO:LiNbO<sub>3</sub> ridge waveguide. The laser maintains a high quality TEM<sub>00</sub> circular beam with M<sup>2</sup> < 1.1 and very low r.m.s. noise of less than 0.06% over the entire range of output power. Less than 0.1% peak-to-peak output power variation was measured during 14 hours of operation. No degradation of the conversion efficiency has been observed for operation at an output power of 70 mW for 3.5 months. The prototype laser has a small footprint of 5x8 cm.
We report on cavity-enhanced second-harmonic generation of 488 nm radiation in a 5 mm long periodically poled KTiOPO4 (PPKTP) crystal pumped by the output of a single-mode 976 nm semiconductor external cavity laser. At a pump laser output power of 660 mW, a mode-matching efficiency into an enhancement cavity of 65 % was observed. A maximum power of 156 mW at 488 nm was generated in the enhancement cavity of which 130 mW was coupled out. Under these pump laser conditions an overall optical conversion efficiency of 20 % and an overall electrical to optical efficiency of 9 % was measured. Both the spatial and spectral properties of the 488 nm beam are of very high quality. Typically, a near-diffraction-limited beam with M<sup>2</sup><1.1 is produced with low astigmatism and little ellipticity.
We report on room-temperature photochromism of Zn- tetrabenzoporphyrine-doped polymethylmethacrylate. A one- quantum, thermo-reversible photoreaction is initiated with the 633 nm line of a HeNe-laser. The quantum yield depends strongly on the concentration of an electron acceptor which is doped into the matrix. The optical density of the sample can be reduced by up to a factor of 5 via irradiation, leading to refractive index changes of about 0.015.