Which laser goes the furthest? A response...

[Alaskan]

Yea, been working with frequency and wavelength most of my carrier as a RF tech/engineer, but for lasers we don't use frequency, we use wavelength. The number is too long if using frequency when talking about different colors of light.

 

[CurtisOliver]

I had a feeling that was why, as I know you deal with RF very frequently. That explains it.

 

[Radim]

Guys, just one more information to add - if you think about the frequency of light, it is better option (however a bit inconvenient compared to nm) - just because its relevance to photon energy. If you consider wavelength, you have to specify in which medium the EM radiation is moving - the speed of light depends on it and therefore wavelength as well - assuming no change in frequency. As conclusion - the wavelength in vacuum would be slightly longer than in air and also from material of your eye, but you would not notice it because you are looking via your eye and also air layer has to be between it and some other environment - just try to focus in water without goggles - impossible.

 

[steve001]

I'm certain how far a laser will go depends entirely how good ones throwing arm is. I think it's safe to say the typical pen style laser would travel farther do to lesser mass than the Hercules style laser for comparison. If anyone asks this question again, I will direct them to this post.

 

[steve001]

Aha, another variable, whether viewing in the dark or not, the peak wavelength shifts down to a slightly longer wavelength for scotopic vision, when your eyes have adjusted to the darkness. That would shift the peak sensitivity down and make the red wavelengths a bit more sensitive to our eyes, but the blue worse. I forgot about this, question is, when viewing a powerful laser beam in the dark, does it shift your vision out of scotopic?

Scotopic sensitivity equals blue light, shorter wavelengths

Scotopic sensitivity only applies to ambient natural lighting. There is no red light available under natural scotopic ambient conditions. A comparison of natural light vs. articial is not applicable because the number of photons entering the eyes is much less than would enter ones eyes from a red light source. If comparing two sources of artificial light blue and red equidistant from the peak of 555nm the one which appears brighter depends on the output. If the outputs are equal they will be equally bright. There is a chart at Sam's Laser FAQ showing the relative brightness at various wavelenghts.

 

[Alaskan]

What do you think of this calculator? Relative Laser Beam Brightness Calculator: (569nm 1mw) vs. (617nm 1mw)

 

[CurtisOliver]

I use it occasionally to do quick checks, but I do believe it to be far too harsh on the blue however.

 

[Alaskan]

Well, that makes sense, my own observations confirm that.

 

[CurtisOliver]

Yes, however it is actually very difficult to create a calculator that is spot on.

 

[paul1598419]

Yea, been working with frequency and wavelength most of my carrier as a RF tech/engineer, but for lasers we don't use frequency, we use wavelength. The number is too long if using frequency when talking about different colors of light.

IDK, as the light from a 532nm laser is actually 563.5 THz. Not really such a big number as 532nm is as much a small number.

 

[Alaskan]

If you use THz, that makes it easy, but because I'm an RF technician, I am used to seeing the number expressed to at least the last KHz, which really is a gross number for our use in that spectrum, RF frequencies are often expressed to the cycle for equipment calibrations. That said, it would be silly to express the frequency of light down to the last cycle or Hertz, or even MHz, we don't use it that way.

 

[Khoonda]

I haven't posted in a while, but this topic is relevant to a purchase decision I was trying to make. I was on the Sanwu Lasers Challenger II page and was trying to chose between getting 470nm@4W or 520nm@1W. I ended up getting the 470nm@4W laser, as I was going to use the laser mostly at night and I knew that our sensitivity shifted a bit to the shorter wavelengths in low light. I figured the blue one would appear brighter. However, according to the calculator, it's still only 77% as bright compared to the green. You said it's "too harsh on blue power," does that mean the blue might have a higher percentage in comparison?

 

[steve001]

I haven't posted in a while, but this topic is relevant to a purchase decision I was trying to make. I was on the Sanwu Lasers Challenger II page and was trying to chose between getting 470nm@4W or 520nm@1W. I ended up getting the 470nm@4W laser, as I was going to use the laser mostly at night and I knew that our sensitivity shifted a bit to the shorter wavelengths in low light. I figured the blue one would appear brighter. However, according to the calculator, it's still only 77% as bright compared to the green. You said it's "too harsh on blue power," does that mean the blue might have a higher percentage in comparison?

You are correct to a point, the caveat is this applies strictly to natural light like what occurs at twilight or pre-dawn. When comparing artificial light you should have chosen green.

 

[Alaskan]

I've compared that amount of power close to 470 nm with 1.3 watts of 520 nm green into the night sky and I found it was difficult to discern which to call brighter (edit: Beam, not spot), but I liked that shade of blue more. Maybe because it was novel for me to have a periwinkle blue beam.

 

[Encap]

I haven't posted in a while, but this topic is relevant to a purchase decision I was trying to make. I was on the Sanwu Lasers Challenger II page and was trying to chose between getting 470nm@4W or 520nm@1W. I ended up getting the 470nm@4W laser, as I was going to use the laser mostly at night and I knew that our sensitivity shifted a bit to the shorter wavelengths in low light. I figured the blue one would appear brighter. However, according to the calculator, it's still only 77% as bright compared to the green. You said it's "too harsh on blue power," does that mean the blue might have a higher percentage in comparison?

What Steve001 And Alaskan have said above +

yes, 1W 520nm is brighter, easier on the eyes, and safer( only 1W dangerous but still dangerous for eyes)

Dot is only 1/2 as bright and beam 77% according to the calculator

You are not going to notice the beam brightness difference very much in a side by side test and the blue is 4X as powerful if you need that output power for anything like burnng power.

Whatever you do be safe wear laser goggles and use safe laser operationand handiling procedures--- 4W can end you eyesight quicker than the blink refles of an eye of 0.25 seconds --there is no chance to correct once an accident is in progress--goggles are they only way.

How bright the beam is depends very much on atomspheric conditions .

It depends on the many factors of air where you are at any given point in time.
Laser beam visibility is highly dependent on ever changing atmospheric conditions and aerosols in the air.
You never actually see the laser beam --what you see is the reflections from particles in the air. No matter what output power 100 mW or 100W or wavelength/color there is no visible laser beam in a vacuum.

At sea-level, one cubic inch (1 inch x 1 inch x 1 inch) (16.39 cm3) of "air" contains approximately 400 billion billion (4*1020) air molecules, each moving at about 1600 km/hr (1000 miles/hr), and colliding with other molecules and anything else they come into contact with about 5 billion times per second. This is the reason for "air pressure". The amount of particles in that air that can reflect a portion of a laser beam's light back to your eye determines if you can see it or not.

It all depends upon atmospheric conditions--a beam you can see extremely well in fog or area with high concentration of particulate matter in the air can be almost invisible in clean clear air

"In a vacuum, the laser beam itself would be invisible - regardless of power or color. As a laser beam passes through Earth's Atmosphere some of the photons encounter large airborne particles which reflect some of the light back to an observer. This only creates intermittent tiny bright flashes of light or "knots" in the beam - it is not why we can see the beam itself.

It is extremely small airborne particles called aerosols having a diameter significantly less than the wavelength of the light that causes the beam to become visible.

The effect of minute particles scattering light is called Rayleigh scattering and it's most noticeable effect is to turn the daytime sky blue. Rayleigh scattering causes photons to be scattered in a roughly spherical manner around these particles. Some of the light is scattered forward (in the direction of the beam), a lesser amount is scattered to the sides and about the same amount that is scattered forward is scattered backwards towards the light source. This backwards scattering is why the beam is more visible to people standing near the astronomer using it, than people standing some distance to the side. The more of these minute particles there are in the atmosphere, the more Rayleigh scattering there is."
From : RASC Calgary Centre - The Atmosphere, Astronomy and Green Lasers

Really you need to understand aerosols in air --is very interesting actually--you need to know what they are locally and density of same to be able to figure laser beam visibility possibilities of one place compared to another place on the earths surface. Example: the most aerosol-laden air in the United States today pales in comparison to Asia. So laser beams are more visible there, generally speaking. Depending on the season and weather conditions, surges of aerosols can make their way into the atmosphere almost anywhere on Earth

See NASA Earth Observatory page for an excellent explaination of aerosols in air with lots of pictures and charts of the planetary distribution of aerosols.
See: https://earthobservatory.nasa.gov/Features/Aerosols/

Probably more answer than you wanted --hope it helps you understand the nature of laers beam visibility.

 

[paul1598419]

One thing I found to be in disagreement with Rayleigh scattering of sunlight through the atmosphere is due not to aerosols, but molecular gases such as N2 and O2. These molecules have a length that cause scattering of short wavelength light causing the sky to look blue, and at dusk or dawn to look more reddish. Apparently aerosols cover a large volume in particulate matter from NO2 to bits of dust which are enormous on a molecular scale. I think most people here are aware of the ability of dust particles to scatter laser light in the visible spectrum. These are more likely indoors, except where smog is concerned in areas where air currents aren't available to carry them off quickly enough to keep them from becoming visible.