`
`W. Sch()ne, D. Golla, S. Knoke. G. Ernst, M. Bode, A Tilnnennann and H. Welling
`Laser Zentrum Hannover e. V.
`Hollerithallee 8, D-30419 Hannover, Germany
`
`ABSTRACT
`
`Diode laser side-pumped, cw Nd:YAG rod lasers operating at pump powers up to 1.1 kW will be
`reponed on. In multimode operation at 1064 nrn, output powers of more than 300 W cw are
`observed. Higher pump powers up to severaJ 100 W/cm can be achieved by using fiber-coupled
`diode lasers as pump sources.
`
`l . INTRODUCTION
`
`Diode-pumped solid-state lasers operating at high cw power levels are attractive sources for
`various applications in materials processing and laser based metrology, because of their reliable and
`highly efficient operation and lifetimes in the range ofseverallO.OOO hours. Low power end-pumped
`solid-state lasers have demonstrated their superiority compared to Lamp-pumped lasers for many
`years 1,2_ But power scaling possibilities of end-pumped configurations are limited because of the
`thermally-induced stress fracture of the laser materials J . Therefore, the transverse pump geometry
`has to be used for output powers beyond 100 W cw 4_
`This contribution reports on the realization of high power diode laser side-pumped Nd:YAG
`lasers in rod geometry. As pump sources linear diode laser arrays as well as fiber-coupled diode
`lasers are used. The laser performance and power scaling of the side-pumped Nd:YAG rod lasers at
`an emission wavelength of 1064 nm will be discussed.
`
`2. ND:Y AG ROD LASERS SIDE-PUMPED WITH LINEAR DIODE LASER ARRAYS
`
`Our first approach to high power systems was based on the application of linear diode laser
`arrays. A detailed description of the experimental setup has been published elsewhere 4; hence, we
`
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`
`
`
`Energetiq Ex. 2050, page 1 - IPR2015-01377
`
`
`
`384
`
`only mention some essential features here. A sketch of the pumping arrangement is shown in Fig. 1.
`The laser rod (diameter: 5 mm. length: 220 mm, Nd-doping: 0.9 at.%) is mounted inside a flow tube,
`which is antireflection coated at 808 nm, for direct water cooling.
`
`The optical pump source consists of
`I 08
`linear diode arrays
`(Jeooptik
`Laserdiode JO LD lOL) with a nominal
`
`output power of 10 W each at 808 run.
`For each pump module, 6 diode lasers
`with similar emission wav.elengths arc
`
`selected. Each diode laser is attached to a
`copper heatsink. The radiation of the
`
`diode lasers of each module is imaged
`into the laser rod by an antireflection
`coated cylindrical lens (diameter: 3 mm,
`length: 80 mm).
`Eighteen pump modules are arranged
`
`in a nine-fold symmetry around the laser
`
`rod yielding a total pump power of
`liOOW at the rod. Pump light reflectors
`are mounted around the rod opposite
`
`each pump module in order to reflect
`back transmitted diode laser radiation
`
`Focussing lens
`
`Fig. I. High power Nd:Y AG rod laser, side-pumped
`by 108 diode lasers.
`
`into the active medium.
`The output characteristics of the side-pumped rod lasers at the laser wavelength of 1064 nm are
`
`investigated in a short, linear planar-concave resonator with a highly reflecting mirror at a radius of
`
`curvature of 5000 mm. A maximum output power of 300 W is achieved at the maximum pump
`
`power corresponding to a pump power at laser threshold of 190 W, and an optical slope efficiency of
`32 %. The wallplug efficiency is determined to about 7 %, the beam parameter product to
`
`approximately 30 mm·mrad. In an 800 nun long, symmetrical resonator with flat mirrors, a beam
`
`parameter product of5 mm·mrad is obtained at an output power of200 W cw. This radiation can be
`
`efficiently coupled into an optical fiber with a diameter of 100 J..Lm and 0.1 numerical aperture (NA).
`
`
`
`
`
`Energetiq Ex. 2050, page 2 - IPR2015-01377
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