# I NIR laser goggles color

#### lucas_

Colors come about because the wavelength is reflected off the object while the rest is absorbed. So orange looks orange because the orange is reflected while rest absorbed.

For laser goggles that is rated for say 532nm (green wavelength). It must absorb the 532nm and so the reflected color won't be green but other colors.

What if the wavelength is 785 nm Near Infrared (visible light is up to 700nm only). What should the color of the goggles?

You can still see slight trace of red for 785nm. But not for longer wavelength. I know the light you see is only 1% of the full intensity of the laser hence I know infrared laser have more safety concerns.

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#### Tom.G

If the Laser wavelength is near the visible range, generally the goggles will be tinted near the opposite end of the visible spectrum. If far away from the visible spectrum the goggles often appear clear, because we don't see the light they block anyhow.

The other important characteristic is how much of the light is blocked. The more powerful the light source the more you want to block. This characteristic is known as Optical Density or OD. OD is on a logarithmic scale. OD of 1 lets thru 1/10 of the light and an OD of 3 lets thru 1/1000. Common density range of goggles for electric arc welding is 5 to 14.

Anyhow, a quick Google search revealed for 785nm they are available in Blue, Green, or Clear.

Cheers,
Tom

#### lucas_

If the Laser wavelength is near the visible range, generally the goggles will be tinted near the opposite end of the visible spectrum. If far away from the visible spectrum the goggles often appear clear, because we don't see the light they block anyhow.

The other important characteristic is how much of the light is blocked. The more powerful the light source the more you want to block. This characteristic is known as Optical Density or OD. OD is on a logarithmic scale. OD of 1 lets thru 1/10 of the light and an OD of 3 lets thru 1/1000. Common density range of goggles for electric arc welding is 5 to 14.

Anyhow, a quick Google search revealed for 785nm they are available in Blue, Green, or Clear.

Cheers,
Tom
I know about the Optical Density and even the formula for determining it given laser wavelength and power.

Why do you think the 785 come in blue or green color? Does it help in suppressing the 785 nm? Or is it only for cosmetic purpose?

#### Tom.G

Why do you think the 785 come in blue or green color?
Many color-selective filters have a fairly wide wavelength (color) band, they are cheaper to make that way. The wideband filters for 785nm would overlap the visible Red wavelengths and block them. When Red-Orange is removed from White light you have Green-Blue left, that's all there is to see.

#### lucas_

Many color-selective filters have a fairly wide wavelength (color) band, they are cheaper to make that way. The wideband filters for 785nm would overlap the visible Red wavelengths and block them. When Red-Orange is removed from White light you have Green-Blue left, that's all there is to see.
Anyhow, a quick Google search revealed for 785nm they are available in Blue, Green, or Clear.
Ok. But you mentioned there was also clear. Why is there clear?

#### Tom.G

Why is there clear?
They are probably made by building up multiple layers of two materials that have a different refractive indices. The individual layer thicknesses are selected to be 1/4 wavelength thick at the wavelength to be blocked. This causes interference between the reflected light and the incident light, and that blocks transmission at the selected wavelength. They are called "Interference Filter" or "Dichroic Filter."

above found with:

Cheers,
Tom

#### lucas_

They are probably made by building up multiple layers of two materials that have a different refractive indices. The individual layer thicknesses are selected to be 1/4 wavelength thick at the wavelength to be blocked. This causes interference between the reflected light and the incident light, and that blocks transmission at the selected wavelength. They are called "Interference Filter" or "Dichroic Filter."
Are the design of these better?

above found with:

Cheers,
Tom

#### Tom.G

Are the design of these better?
Aww, come on. What is your definition of 'better?' There are always tradeoffs.

The interference filters can block more of a specific wavelength while letting thru others, so you can see what you are doing. But there cost is substantially higher and they are a bit more prone to scratch damage that destroys their filter capability.

#### Dr Transport

Gold Member
If I remember correctly, poly-carbonates block IR very well and are clear, that is the reason a pair of goggles for NIR are not tinted, other than for the higher OD.

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