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405nm Laser Violet Pointer

405nm Violet Laser Pointer


Violet laser diodes are becoming more common thanks to the popularity of the Play Station 3 and Xbox 360, and with the Xbox 360 being discontinued cheap surplus sleds are becoming available. I decided it was about time to try making a laser pointer myself, so I picked up a PHR-803 sled from ebay. Laser diodes are sensitive devices, and will burn out if not treated carefully. To begin lasing a diode can require up to 80% of  the current it would take to kill it, so the margin for error is small. The only practical way to drive a laser diode is with a constant-current source, and carefully watching the power output. For driving small laser diodes I've made a simple constant current source.

Schematic

The circuit works by measuring the voltage across the 5.6 Ω resistor, since the voltage across the resistor will be proportional to the current flowing through it. The voltage is kept small to lower power dissipation and prevent necessitation of a larger voltage source. Because the voltage is so small it is amplified by a non-inverting amplifier. Adjusting the gain of the amplifier allows the magnitude of the sensed current to be adjusted, allowing a wide range of regulation currents. The measured current is compared to the stable reference voltage provided by the TL431, and an error is sent to the BD139. The op-amp will attempt to keep the measured current signal equal to the reference signal, and thereby keep the current constant by constantly adjusting the base current to the BD139. The 1N5815, 1µF capacitor and 22nF capacitor are for protecting the diode from ESD, reverse voltage, etc. I've made a spreadsheet calculator to ease modifying the circuit for different regulation ranges. Download.

Driver with laser

I tested my laser between 60 and 90 mA, though it's said to tolerate 110mA. Burning stuff can be done with DVD lasers, so I don't plan on pushing my violet diode. I had to look up the pin out at "Laser Pointer Forums", since I failed to determine it empirically. This is what the pin out is:

Laser Diode pinout

Here are some images of the beam before collimation, ie from the bare laser diode. When purchasing bare laser diodes remember that they require additional optics to make a nice laser pointer beam. Commonly something such as an "Axiz module" or the optics from an old laser pointer are scavenged for this purpose.

uncollimated beam  Fluorescence of phosphors          

Lacking an Axiz module and not being able to collimate the beam properly with an old laser pointer collimator, I opted to build one myself. The final focusing lens from the PHR-803 was taken and mounted on a transformer lamination, while the diode was mounted on a segment of aluminum heatsink. With two screws I could crudely adjust the position of the lens and more or less collimate the beam. The result isn't too bad, but the diode and lens are a bit off center, visible by the lines in the beam. The lines originate from the lens, which is some type of Fresnel lens.

collimator  collimated beam

Youtube video of fluorescent stuff being shown upon.



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This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.

Disclaimer: I do not take responsibility for any injury, death, hurt ego, or other forms of personal damage which may result from recreating these experiments. Projects are merely presented as a source of inspiration, and should only be conducted by responsible individuals, or under the supervision of responsible individuals. It is your own life, so proceed at your own risk! All projects are for noncommercial use only.