Laser Kids
RUS

. : The table to be used for visual determining of laser power : .

 

VISIBLE LASERS ONLY The spot is weak but definitely able to be recognized when the beam hits white surface and the ambient lights are not too intense 0.01 - 0.1 mW  
The laser spot is easy to notice except maybe a sunny day 0.1 - 1.0 mW  
The brightness of the spot is comparable with the very common cheap red laser pointer or He-Ne laser 1.0 - 10 mW  
The spot is easy to observe from a distance even at the surfaces lit by sun 20 - 100 mW  
ANY LASERS (including infrared and ultraviolet ones) Able to lit a match 50 - 100 mW 50-100 mW
Able to cut down a match into the halves 600 mW - 1 W 600-1000 mW
Able to ignite inflammable materials (like paper, cardboard or plywood) to visible and stable flame > 3W 3 W
Able to cause vigorous burning of inflammable materials (cardboard,
plywood, etc.)
10 W 10 W
Able to hack down (to slash) a match 40 W 40 W

 

COMMENTS:

Understandable that one can visually estimate power of a laser only to a very rough extent. Especially this is true for the weak visible lasers. The visibility of the laser spot depends strongly to the wavelength (colour), to the size of the spot, to the reflective and diffusive properties of the screen, to the power of ambient illumination and even to the individual specialties of the sight: one may have more sensitive eyes while the other may have more rough ones. Amazing here the fact that one can certainly see a spot of a beam having as low power as 10 microwatts and it is still being sensed as one having "normal" brightness. This fact often misleads people to attribute microwatt rated lasers as milliwatt ones.

Need to note that the eye sensitivity has logarithmic character. Generally it means that large differences in power correspond to moderate variations of visual brightness. And the higher power level we deal with the lower will be the perceived difference.

The heat action of the laser beam is more objective. But the specialties take place even here. I.e. the reflectivity of metals grows strongly with growth of the wavelength. And, say, to burn through a leaf of aluminum foil, an easy task for some moderate power blue laser pointer, requires serious power from a neodymium laser, and turns out to be a very hard task to a CO2 laser. On the contrary CO2 laser easily burns and cuts glass parts, while to do the same is almost impossible for visible lasers.

All the phenomena, given in the table, are to be made by a focused beam. One should focus the beam by a lens having its focal length equal to 1..2 inches. Usually, when the necessity uprises to estimate a power of some laser such a lens is easy to get somewhere around. The exclusion may be formed by CO2 lasers, one must use special lenses for them (like ZnSe or germanium ones) or by short ultraviolet lasers (fused silica, salt, sapphire).

 

One may suppose that the possibility to perform a given action by some laser strongly depends to the sharpness of focus. But in reality it is not completely true. The mentioned in the table phenomena are to be performed by a laser and/or the target being handled by hands. Tremor and small errors of aiming bring all the bonuses of narrow focusing to naught. In practice it is enough to narrow the beam to 0.3..1 mm. Moreover, the ability of a laser to enflame something does barely depend to the spot diameter in range between zero and several millimeters.

 

Also the possibility to perform one or another action mentioned in the table should be treated as the possibility to do it without too hard efforts. For example one can light a match by a 15-20 mW rated He-Ne laser, but it requires reliable fixation of the laser, the match and the lens. It also requires to seek a "sweat spot" on the match head. And finally it requires many tries and waiting for a long time. So hard efforts are out of considerations meant here.

Here is just another video to compare the effect with power. The show was performed with a blue 5W rated laser diode. Evidently the red and infrared lasers won't be able to cut through a steel so easily.

 

 

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