My suggestion if you just HAVE to use a laser to attract lighting
Step 1. Make a long laser host out of copper or other highly conductive metal
Step 2. Tie a non-insulated copper wire around the laser, and then tie the laser to a 12 foot pole. Tie the other end of the copper wire around your right wrist.
Step 3. During a nice thunderstorm climb a high mountain, then climb the highest tree on the top of the mountain.
Step 4. Tie a LONG length of non-insulated copper wire around your left wrist. and throw the roll to the ground so it rolls across the greatest distance of ground below you.
Step 5. Hold the long pole, with your laser above your head as high as it will reach.
Step 6. Wait for the bright light.
The advantage to this method is you can STILL attract a lightning bolt with a normal <5mw laser pointer! you don't even need those high powers. Why even turning the laser on is purely optional!!!!
There are some side effects to this method. However, there are actually fewer side effects to worry about then using a terrawatt laser to do it! after all, this way there is no need for the added risk of blinding anyone or anything. The inevitable electrocution is of course a risk factor to any method of attracting lightning with a laser pointer
(I couldn't resist. I'm surprised nobody beat me to this)
Now here on earth, in the land of reality, there will be no lightning guns anytime soon. If you could use a laser to move something conductive into the air this would be a different story. However, as far as I know, you can't use a laser to launch mercury vapor into the air in a solid stream. You are better off launching the model rocket ideas mentioned before. Those actually work well by comparison. you can enhance the model rocket lightning strike by finding the right spot. Geology of where you are standing plays a large part in lightning strikes. After all, the old spanish gold miners in the north american west used to have an interesting method for finding ore. It involved sitting on a mountaintop in a thunderstorm and watching if there were any places lighting strikes more often. Any place struck repeatedly needs to have some structure in the ground changing potentials. It's not always conductive ores like silver and gold. Lightning ridge in australia was named for guess what? that's right. lightning. The ground with rich silica deposits also had a large amount of geothermal heated water rich with minerals. Left it nice and conductive. As an odd note that geothermal water rich in silica is what deposited the opals the area is famous for. Sometime you should head to Virgin Valley nevada. It's got a similar structure in the ground (also similar opals) more water though in nevada. Been there during a thunderstorm. You can see lightning strike down in the valley more then up at the ridges around it. Made me a little worried being camped at the ccc spot with the warm springs.....
, with a 3 cm beamwidth at 800nm (IR), fired from a mountaintop.
