North City Tech Group

A real laser made from household scrap

Click on picture for detailed view: picture made, using slow shutter iPhone app, by moving fluorescent target along beam path

Follow up to presentation

Here's a very brief and detailed view of the laser output on a fluorescent target. The power source is a cheap HV module, exactly like the HV module that was featured in the presentation. My apologies for the annoying sound - the spark gap is quite loud. Use hearing protection when operating these lasers!

Here's a very brief teardown and reassembly of the laser. It provides a little more visual detail than was possible in the formal presentation.

Raised Edges of Saddle Threshold

More on the power supply

The high voltage module can be purchased on eBay for a few dollars. It is falsely advertised as being a "3.6v-6v to 400kV 400000V Boost Step-up Power Module High Voltage Generator", but anyone with high voltage experience can recognize the obvious exaggeration of this claim. For my demonstration I connected the input to the 3.3V DC output from an ATX power supply and measured around 2.7V DC across the input to the module at a current of 2.4 Amps. With 50 Ohms resistors across both sides of the module output, a small xenon camera flash did not become hot as it did during previous test (with no resistors at the output, and an input of 4.5V at 3.3 Amps.

Determining output polarity

Basic diagram of laser - click on image for larger view

Longer Electrodes

Although the theoretical limit of the channel is 9 1/2 inches based upon an 800 picosecond pulse (only a 4-3/4 inch long channel, if a rear mirror is included in the design), this limitation is possibly more applicable to a design that is optimized for maximum efficiency. I've obtained good results with longer channels, even using thicker dielectrics such as plastic signs (see image below). With the longer channel, tapering is easier (for greater output at the wider end) because the difference in separation is more resolvable, for a given angle, than it is for a shorter channel.

Click on image for larger view

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