What Color Will NIR Laser Goggles Be?

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Discussion Overview

The discussion centers around the color of goggles designed for use with near-infrared (NIR) lasers, specifically those operating at a wavelength of 785 nm. Participants explore the relationship between the wavelength of light, the colors of the goggles, and the principles of optical density and filtering. The conversation includes technical aspects of how goggles block specific wavelengths and the implications for visibility and safety.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • Some participants explain that colors are perceived based on the wavelengths reflected and absorbed, raising questions about the color of goggles that absorb 785 nm light.
  • It is noted that goggles for wavelengths near the visible spectrum are typically tinted in colors opposite to those wavelengths, while those far from the visible spectrum may appear clear.
  • Participants discuss the concept of Optical Density (OD) and its logarithmic scale, indicating how much light is blocked by the goggles.
  • There is mention of the availability of goggles in blue, green, or clear for 785 nm, prompting inquiries about the reasons behind these color choices.
  • One participant suggests that wideband filters for 785 nm may block visible red wavelengths, resulting in the perception of green-blue light.
  • Another participant describes the construction of clear goggles using interference filters, which block specific wavelengths through layered materials.
  • Concerns are raised about the trade-offs between different filter designs, including cost and susceptibility to damage.
  • A participant mentions that poly-carbonates can block infrared light effectively while remaining clear, suggesting a reason for the lack of tint in some NIR goggles.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the color and design of NIR laser goggles, with no consensus reached on the optimal characteristics or reasons for specific color choices.

Contextual Notes

Discussions include assumptions about the effectiveness of different materials and designs in blocking specific wavelengths, as well as the implications of optical density on visibility and safety. The conversation does not resolve the effectiveness of various goggles or the best practices for their use.

lucas_
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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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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 let's thru 1/10 of the light and an OD of 3 let's 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
 
Tom.G said:
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 let's thru 1/10 of the light and an OD of 3 let's 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?
 
lucas_ said:
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.
 
Tom.G said:
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?
 
lucas_ said:
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."

https://en.wikipedia.org/wiki/Interference_filter
above found with:
https://www.google.com/search?&q=optical+interference+filter+design
Cheers,
Tom
 
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Tom.G said:
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?

https://en.wikipedia.org/wiki/Interference_filter
above found with:
https://www.google.com/search?&q=optical+interference+filter+design
Cheers,
Tom
 
lucas_ said:
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.
 
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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