But now still wondering what makes a good LPM? Some more knowledge about LPM will be appreciated.
Basically, the sensitivity, the repetitivity, and the precision and calibration, are the better things to look in any LPM, also with insensitivity in differences of measured wavelenght .....
I mean, if you need to test low-powered lasers, you need a LPM that is sensitive enough to measure also them with a decent accuracy ..... repetitivity, i mean it as "if you take 10 measures of the same laser in the same conditions, they must be identicals" (or, at least, reasonably identicals) ..... precision and calibration are obvious things, as for any measure instruments, you need an LPM that measure the correct amount of power from the beam (no need to get a 0,01% accuracy lab unit, for take on-the-fly measures in a shop, but if you want a decently accurate measure, you need at least a 5% or more precise unit) .....
About the insensitivity to different wavelenghts, this is a separate argument ..... there are basically 2 different types of LPMs (well, there are 5, in fact, but you don't need them, so basically the classes of LPMs that can be used in a shop are 2) ..... photodetectors and thermal detectors ..... photodetectors are the more sensitive type of measuring heads, for laser powers (they can measure microwatts), but they have also the inconvenient that they are extremely sensitive to differences in wavelenghts ..... the photodiodes used for them, none of them have a "flat response curve" to different wavelenghts, so, for use one of them, you need to know both the different wavelenghts of the laser that you are measuring, and the correction chart for the different wavelenghts, and after, you need to multiply the reading for the correction factor for that specific wavelenght, for get the real value ..... can not give too much problem, for a private, but in a shop, i guess it can be a real pain you-know-where
.....
The second class of LPMs is the one that uses thermal sensors, or "thermopiles" ..... there are two different types, of sensors called thermopiles, one is made using Peltiers sensors in reverse use, and one is made using a lot of bimetallic junctions "printed" on the back of a very thin disk, painted on the reading side with substances that ensure the maximum possible light absorption ..... the first type (peltier cells) are a slightly less sensitive to very low powers (but there are some good ones, like as example the ones that Jerry sell), and can have a slight thermal derive for prolonged reading cycles, but are almost ininfluent to the point where you hit the sensor with the beam (i mean, the reading don't change too much if you point the beam on the center or on the borders), and are less delicate and cheaper than thermopiles ..... bimetal thermopiles are more sensitive to low powers, and intrinsecally less sensitive to thermal derive from prolonged reading cycles, but must be used pointing the beam the more centrally possible, for have a correc reading, cause are more sensitive also to the point where you point the beam (mean, pointing at the center, you have the correct reading, where pointing at the borders, you read more power than the real one), and are more delicate and have higher costs .....
Will different lasers need different IR? For example, will a IR for 532nm do well in a 650nm laser's test ? And it will be perfect, if some information about the price is given
Well, no, only green DPSS (or, more precisely, all the DPSS types of lasers, but mainly we speak about green, speaking about IR leaking), have IR leaking ..... this cause the green light is obtained "pumping" infrared light in the crystal that double the frequency, so part of the IR light (both 808nm and 1064nm) can leak out with the green ..... if the module is well built, with crystal sealed in the heatsink and AR / HR layers well done, the IR leaking is minimal, but usually "commercial" (read "cheap"
) pointers uses simply a glued crystal set, glued in a corner of the heatsink holder, without any seal, and with only an AR coating, so the IR leakage is higher (and, ofcourse, worse is the building, more is the IR leakage) .....
Laser diodes does not have IR leakage at all, they lase directly in the declared wavelenght, so there's no need at all to filter out IR from them, they just don't produce it.
Hope this was that what you want to know, if you need any other informations, just ask :beer:
