We describe a compact and efficient Nd:YAG waveguide laser pumped by a diode-bar. An output of 1.5W is obtained for 6W incident power, with significant brightness enhancement

Bonner, C.L.

Brown, C.T.A.

Clarkson, W.A.

Hanna, D.C.

Shepherd, D.P.

Tropper, A.C.

English

Southampton (e-Prints Soton)

1.5W Diode-Pumped Monolithic  Planar Waveguide Laser D.P.Shepherd,  C.T.A.Brown, C.L.Bonner, S.Guy’, W.A.Clarkson, D.C.Hanna,  A.C.Tropper, and  B .Ferrand+ Optoelectronics  Research  Centre,  University  of Southampton,  Southampton  SO1 7 INP,  U.K. Tel:  +44  1703 594523,  email:  dps@orc.soton.ac.uk ‘LPCML,  Universite’ Claude  Bernard  Lyon  I,  Villeurbanne  Cedex, France ‘LETI  (CEA-Technologies  Avancebss),  C.  E.N. G., 85X-38041  Grenoble  Cedex, France . . Abstract We describe  a compact  and efficient Nd:YAG  waveguide  laser  pumped  by a diode-bar. An output of 1  SW is obtained  for 6W incident power, with significant brightness  enhancement. l.SW Diode-Pumped Monolithic  Planar Waveguide Laser D.P.Shepherd,  C.T.A.Brown, C.L.Bonner, S.Guy*,  W.A.Clarkson, D.C.Hanna, A.C.Tropper, and  B  .Ferrand+ Optoelectronics  Research  Centre,  Universic  of Southampton,  Southampton  SO1 7 INP,  U.K. Tel:  +14  I703  594523,  email:  dps@orc.soton.ac.rtk ‘LPCML,  Universite’ Claude  Bernard  Lyon  I,  Villeurbanne  Cedex, France ‘LETI  (CEA-Technologies  Avanceis),  C.  EN. G., 85X-38041  Grenoble  Cedex, France Diode bars are now being widely  employed as pump sources  for  solid state lasers. However, their output is highly elliptical  with  one axis being typically  >lOOOX diffraction limited.  This makes it difficult  to use them for longitudinal pumping where small-diameter .  .-  circular beams are normally required.  Here we report the longitudinal pumping of a planar waveguide  laser  by a diode bar. The  planar waveguide  has  the advantage  of being compatible with the elliptical nature  of the diode beam,  simplifying the focussing  requirements  and leading to a very compact  laser source. The guidance  of the pump and signal radiations also leads  to a very good spatial overlap. and consequently  efficient operation, without the need for careful resonator  alignment. Figure 1 shows  the experimental set-up  used  in these  experiments. The diode-bar was collimated in the vertical  direction to a beam  diameter  of 325pm with a fibre lens. The M’ values of the beam after  the fibre lens  were found to be 2.4 and  -3000 in the vertical and  horizontal axes respectively.  Focussing in the vertical plane was achieved by expanding the beam with  a cylindrical lens telescope  and  finally  focussing  into the waveguide  with a 6.25mm focal length cylindrical  lens.  Focussing  in the horizontal (non-guided) plane was achieved with  a single 19mm focal length cylindrical lens. This lens array produced  a 25pm by -1mm  (radius) line focus with a maximum power of 6W.  The lenses  are all glued permanently in position and so very little alignment is required  in the final system. The planar  waveguide  used  was  grown  by liquid-phase  epitaxy and  consisted  of an 80pm thick Nd:YAG  core with  YAG  substrate  and cladding layers.  The end-faces  were cut and polished  plane and  parallel to give a cavity length of Smm. The faces  were coated,  forming the laser  cavity, with a nominally high reflector at one end and a 5% output coupler at the other. Figure 2 shows the laser performance  obtained  with this waveguide. A 39% slope efficiency with respect  to incident power was obtained  with a maximum output power of 1  SW.  With the guide aligned for maximum power the output was observed  with a CCD camera  to consist  of 3 lobes  in the guided direction and single-lobed  (although not smooth) in the other direction. M2 values  of 5.2 and 89 were found in the guided and non-guided  planes. It was found that with a small vertical adjustment  the output appears  single lobed in both directions and the M2 values are  reduced  to 3.6 and  72. Under  these  circumstances  the output power is reduced  to 1.2W. This is a more than 5-fold increase  in brightness  compared  to the incident pump beam. Future work will  concentrate  on improving the focussing  lens array via the use  of fibre lenses, to  allow  smaller guides, which  support a smaller number of  modes,  to be used. Combining this with tighter focussing  in the non-guiding  plane  should  lead to further significant improvements  in the M2 values. 

1.5W diode-pumped monolithic planar waveguide laser

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