Laser Kids

. : Read this when you got tired to fail : .


  1. I already know that nobody reads such texts, but nevertheless...
  2. Power Supply Unit is the Head for everything.
    If the leaks are small the storage capacitors of a pulsed laser can be charged by an electrostatic machine or even by means a of a comb and a cat... But such tricks are successfull only when being performed by people already experienced in laser techinique. If You are a beginner, I insist You to begin with obtaining some proper power supply unit.
    What does it mean "proper"?
    Its voltage must provide at least 20% surplus over the voltage needed for Your laser project. The double excess is even better.
    For continuous (CW) lasers the power supply shuild be able to provide current triple times larger than the one corresponded to the expected lasing threshold.
    For pulsed (QCW) lasers the power supply unit should be able to provide enough power for the laser to fire at least once per second.
    The first deed for You to begin with - is to buy or produce a high voltage power supply having the needed voltage and power. Then one should "play" around" with it for a pair of weeks: to charge some Leyden jars, to make some sparks (KEEPING IN MIND THE SAFETY RULES HOWEVER) - to get used to the high voltage possibilities and behaviour.
    And only then one might proceed further.
  3. Power meter is our holy artifact.
    To tune a working laser gives more fin and better results than to tune an unworking one. But You should be at least able to detect the fact of lasing. The things are simple with dye or nitrogen lasers - if one can not see a laser spot then there is no lasing at all. And one has little chance to lie to himself in this case.
    Another situation is with invisible lasers. An beam of low quality and large diameter can be barely focused. So one can not hope to burn a spot on carbon paper. In practice a beam of an invisible laser can be reliably seen beginning from the average power over 100 mW for continuous lasers an from the pulse energy over 10 mJ for the pulsed lasers. And these values are valid if You have some means to focus the beam (for CO2 lasers one needs at least a zinc selenide lens or a first surface spherical mirror). If one has no means of focusing, the numbers should be corrected by an order of magnitude. I.e. about 1 watt for continuous laser and 0.1 J for the pulsed one.
    Get ready for that Your laser will not produce that power without some tuning and optimization, and if You will try to make that tuning even without knowing whether Your laser does lase or not, You risk to make it only worse.
    So the next thing You should make or obtain after the power supply is a power measuring (power detecting) device. Even a simplest calorimeter will be better than nothing.
  4. Laser helps to build another laser.
    Only a few lasers can operate without mirrors. And if You are going to advance from the simplest nitrogen ones You will meet the necessity to deal with so called "alignment" process - the procedure of setting the mirrors to be parallel to each other while providing the axis orthogonal to both mirrors to go freely through the laser medium.
    There are many ways to make the aligning and there are many devices that can help this deed.
    At the present time the very tool to make the alignment possible is an auxiliary visible laser of low power: so called "alignment laser". The third thing to obtain after the power supply and the calorimeter is the alignment laser.
    The best results can be achieved using a helium-neon laser. It is rubust and reliable enough. However it is rather expensive and rather rare. It is simpler to look for some laser pointer or laser diode from DVD drive with simple collimating lens. Remember that the alignment is time consuming, so the laser should be able to be powered from the mains. Or, in case of batterry power, the batterries should be large enough.
    Concerning the power of the alignment laser, one can say, that 10 mW rated red laser is more than enough to align almost any laser that You are able to create at home. On the contrary, more power will only fatigue Your eyes (may result in headaches) and also will fall into troubles with overheating. Exactly due to the mentioned overheating problems it is unwise to use green laser pointers (of DPSS type) even if their power is low. The other parameters of those green laser pointers are good enough for use for the alignment purposes.
  5. The larger laser You are starting to build, the more... epic fail You will get.
    "To cut plywood I need a 100 Watt laser. A CO2 laser has its efficiency of 10% and gives about 80 watts per meter. So i will need a kilowatt rated power supply and the tube length I will take with some surplus, like 1.5 meters. These digits look nice. I definiely should build one..." - this is an example of typical noob-thinking, resultung in a pile of glass tubes (and other parts) lying in a corner of the garage for five or more Years... This pile of parts occupies room and does not do anything useful...
    The same can be said about solid state lasers. There are too many offers over the internet to buy a large or a very large laser rod. They cost damned high and (if used properly) they are really able to give enough laser energy to shoot down a duck. But there are many such offers and there is lack of real laser gun... So:
    Especially be carefull when chosing ruby or laser glass rods. Those materials are especially hungry for the pump power. The things are easier with YAG:Nd. It has four-level lasing scheme and high gain per unit of absorbed energy. Both properties result in that an average amateur can easily pump a crystal of almost any size of being commercially offered.