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R7 Final Version
r7fosc.jpg (Actual photo)
r7fosc.gif (Schematic) Dual flashlamps were wire wrapped from cathode up to beginning of anode arc (about 1 inch from anode terminal to provide better ground plane for easlier triggering)
frao1.jpg Pulse recorded with CCD camcorder on black board. Single longitudinal mode. Below some indication of transverse mode quality..
fr7o2.gif 3d view of recorded pulse. fr7o5.gif 3d view of 2nd recorded pulse Refer to r7beam.htm regarding recording setup and image processing procedures used to process the above recorded CCD camcorder on black board image.
fr7o3.gif Ideal beam
New modification for version 7: Dual flashlamp oscillator. Beam quality M2 value was approximately 2.1 at 13.2mj with 1.2mm aperture (1.01 Fresnel number) as calculated by measuring the beam waist from a 150mm plano-convex lens**. Reference: :http://www.uslasercorp.com/Envoy/m2.htm This beam quality measurement indirectly suggests possible mulitmode output (TEM00 mode + smaller percentage of some higher modes combined due to larger spot size). But there is another factor effecting M squared for solid state lasers as they generally have thermal lensing effects. For Q-switched ruby lasers, the laser has a negative lens effect at the time of q-switch output and will increase spherical aberration effects with increasing pump input. These effects contribute to a change in beam divergence. Since this is a holographic laser, this M2 value doesn't reveal wavefront errors and phasefronts critical to holograms that might be revealed with a Shack-Hartmann sensor. The beam quality rests on clean and good quality oscillator and amps and the rest of the optics system to provide good quality holograms. The amplifiers for example will reduce the beam quality M2 value due to this thermal lensing aberrations by increasing divergence yet won't change the TEM content. Overall the beam quality as viewed from a ccd camcorder (see contour maps above) and after being focused showed tight focus with nice beam symmetry at focus suggesting the beam quality approached toward diffraction limited gaussian quality but only at a reduction in output (around 11mj or less).
Finally R7-MOPA will be upgraded by installing a larger diameter flashlamp SG-2800 modified for the amplifiers to remove hot flashlamp further away from rod reducing potential thermal surface damage to laser rods.
** Careful beam centering on Plano-convex lens with shape factor +1 (curved surface toward laser). Repeated pulse firings to find minimal spot size. More precise spot measuring. Measured beam spot value was .005 inch and calculated gaussian spot size 59 inches away from OC was 0.0034 inch based on Thorlabs lens 150mm FL but at 694.3nm was found to be around 162mm from the beam measurements.