Home Return to Main Page


Version 9 All water-cooled with pump and filters, oscillator and amplifier changes.

Because of holographic film issues, it was determined that a higher output holographic laser would be useful. First the air-cooled dual lamp 7mm cavity will be replaced with a 3/8 inch by 6-inch dual lamp water-cooled unit. The mirror separation was increased to 21.5 inches to accommodate the larger cavity head. The 5-meter concave HR mirror was kept. Removing 1 plate of the 4plate resonant OC allowed the peak reflectivity would be around 65% for good slope efficiency. The aperture was set at 1.06mm. These changes will help ensure TEM00 mode and enough energy output. Since the laser was operating in single axial mode it was easy to see occasional single TEM01* or a single TEM10 mode develop. At 1.06mm with a Fresnel number around .61, this causes a high diffraction loss insuring TEM00 mode.

rw9h1.jpg  photo of new oscillator install in the laser.

Here is a ccd photo of the Tek 2465B 400mhz scope capturing the oscillator pulse. xa1.jpg

Output of the oscillator was a single 5 nanosecond 34mj pulse and single mode both axially and spatially. Each lamp was fired separately from a 915ufd bank of four 3900 ufd/400volt electrolytics. It was found that a 34-43mj pulse was possible, but inorder to keep single mode, the voltage was dropped and q switch concentration was adjusted. It was found that at 1250 volts (1440j input) a single 9.83mj 20ns pulse could be achieved, but if voltage was raised to 1350(1700j) to 1400v the pulse would split into two 15ns pulses separated by 50ns. At full power of 1600volts 2320joules the double pulse was 5nsecs each. Due to the 6 inch long laser rod and efficient pump cavity, the single pass gain of the system became too high for the qswitch dye relaxation time and the q switch double pulsed.

rw9ps1.jpg  Power supply. rw9ps2.jpg  Oscillator modification to Power supply. Added 4th cap to each circuit.

The power supply was modified from 3 caps to 4 caps which based on the lamp impedance allowed a damping factor of 0.8 and the flashlamps were run at 25 percent of explosion limit yielding a expected lifetime of 153,000 firings. The lamps are ILC L-8476 lamps that are have a 5.5-inch arc length and 0.47 inch outside diameter. At 34mj input to amplifier 1 and 2 both of these amps had to be run slightly above threshold at 1400 joules to each amp and the measured output was 1.747 joules. Since the amplifiers are minimal powered, this laser could output three or more joules but the energy density would be too much.

The water pump/cooler system is made of a modified 400 watt pc power supply to power two 48-watt TEC coolers and fans to will remove heat from the closed loop system. This cooler is basically a stainless steel tube with 1/8-inch pipe threads and nylon barb fittings. Then the tube is place in an aluminum heat spreader block, which has a TEC cooler on each side with an aluminum heatsink and fan on each side as well. Surrounding the middle of the cooler is filled with foam. Total amps are 8.4 amps at 12vdc. The power supply mains are tapped inside the pc power supply to provide ac power also to the water pump. The pump is a Danner 250gph with a 20gph at 6-foot head or about 13.8 psi. http://www.pondmaster.com/Specifications/specifications.htm The deionizer is a separate bed type instead of the mixed bed type, as the water resistivity does not need to get too low to prevent metal scavenging. The filters ordered were FF09H1 0.22um 1000cm2 filter, which comes with 3/8-inch hose barbs and side valves to allow air to be released during priming. The deionizer was a separate bed type but without the oxygen absorber model SB18H1 which comes with 5/16 hose barbs. Both filters are from APS Water. The particle filter is expected to drop 5 psi at 3 liters per minute flow.

Pictures of the water cooler setup with filters. water1.jpg water2.jpg cool1.jpg cool2.jpg

Name brand distilled water was measured to have a resistivity of 333K ohms per centimeter. Soft tap water was measured at 35K ohms/cm. After installation of the separate bed filter, the resistivity rose to 950K ohms/cm. Measured PH of soft tap water was 7.3 and the distill water was measured at 5.8 which is normal measurement for an open container due to CO2. http://antoine.frostburg.edu/chem/senese/101/matter/faq/is-distilled-water-a-solution.shtml

The PH in the water system was measured at 7.6 but in an open container it dropped to 6.5. The PH meter was a Hanna Phep+ model HI-98108.