# Presentation: 062948

## Authorizing Alignment Eyewear 

**Authorizing Alignment Eyewear**

- Ken Barat
- LSO
**Lawrence Berkeley National Laboratory**

**2008 LSO Workshop, Albuquerque, NM**

**Notes:**
good morning everyone. My talk will be about a laser-driven accelerator developed at LBL that can produce GeV electron beams on the order of a centimeter.

Before I begin I thank our collaborators and various other supporters of this project.

## Laser Protective Eyewear

- Goal of laser protective eyewear is to reduce any laser radiation transmitted through laser protective eyewear to a level which will not cause an laser injury

## What does ANSI Z136.1 say?

- 4.6.2 Protective Eyewear (Class 3B or Class 4)
- Laser protective eyewear shall be specifically selected to withstand either direct or diffusely scattered beam.
- The default OD for eyewear is that which will protect the user from a direct hit
- The term “Alignment Eyewear” is never mentioned in section 4.6 Protective equipment
- The closest the standard comes is in 4.6.2.4 Factors in Selecting Appropriate Eyewear
- Visible light transmission requirements and assessment of the effect of the eyewear on the ability to perform tasks while wearing the eyewear

## Laser eyewear in the real world

- Full Protection – Will have an optical Density (OD) sufficient to attenuate a direct beam for up to 10 seconds.
- Alignment level- Has an OD lower that that to protect from a direct exposure, which will allow visibility of the laser beam.

## To be very clear 

- We are not talking about impact resistance

## What are we talking about ?

- The ability of a user to see visible beams through laser protective eyewear
- Not seeing a reflection off a sensor card.

## Alignment eyewear

- Lets me very clear laser eyewear used for alignment by definition will not protect one from a direct beam exposure
- Like a bullet proof vest against a knife
- But it has advantages
- It allows visualization of visible beams where full protection does not.

## It is clear that at times, such as alignment of visible beams, the beam needs to be seen

- This can be accomplished in several ways:
- Lowering or attenuating beam output to a 3A level with no use of eyewear
- Using remote viewing aids, CCD, Web Cam that do not place the user over the beams
- Use of co-propagating beams
- Using alignment eyewear
- Removing full protection eyewear or peaking over the top

## Suggested guidance on selection alignment eyewear 

- For Continuous Wave lasers, the alignment eyewear should low the irradiance to a Class 3R level (that is 3A to some).
- It is pulsed lasers that the challenge arises, our recommendation is that the Alignment OD be no more than 1.4 OD less that full protection.
- Before allowing the use of the alignment ,the users set up be reviewed.

## There is some guidance out there

- EN 207 & EN 208
**Scale #****	****	****OD****	****CW  Laser (W)****	****	****Pulsed (J)****	**
**R1****	****	****1-2****	****	****0.01****	****	****	**** 2x10-6 ****	****	****	****	****	**
**R2****	****	****2-3****	****	****0.1****	****	****	****2x10-5**
**R3****	****	****3-4****	****	****1.0****	****	****	**** 2x10-4 ****	****	**
**R4****	****	****4-5****	****	****10****	****	****	**** 2x10-3 ****	****	**
**R5****	****	****5-6****	****	****100****	****	****	**** 2x10-2 **
**Also discusses minimum VLT, 20%****	****	****	****	**

## LBNL history and search

- Our main question was femtosecond laser pulses
- We contacted Bio-effects experts
- Leaders in laser safety
- Experienced eyewear salespersons
- Literature searches
- Spoke with users
- Conclusion.......

## Conclusion

- No clear path exists

- It is a problem not easy to get around

## Pulse recommendation

- Alignment eyewear providing protection from stray reflections from uncoated surfaces, typically ~4% of the direct beam.  OD reduction ~1.4

## LSO approval and documentation

- The bottom line is by allowing the use of alignment eyewear the LSO is allowing the laser user to wear eyewear that does not lower transmitted irradiance below the MPE
- All the good intentions are there but:
- We are placing them at risk

## Therefore

- The authorization or approval should be on a set up by set up basis
- Only good for 1 year
- Based on an actual site visit
- User awareness of eyewear limitations is critical
- Next is the sign off portion of the form we use at LBNL

## Sign off portion

**Alignment eyewear approval**
- As LBNL LSO I approve the use of laser alignment eyewear within the context of the above AHD. This approval is based on my evaluation of laser alignment controls, present beam set up & outputs as demonstrated to me by:
- _	__	__	__	__	__	__	__, _and the assurance that this technique and controls will be followed by all authorized to perform laser alignment.
- Prior to the use of alignment eyewear the user must check for stray beams and take all practical steps to reduce the intensity of the laser beam(s).
- Approval granted on_	__	__	__	__, expires one year from this date._
- _	__	__	__	__	__	__	__	__	__	__	_
- Ken Barat, LSO

## Laser Safety Chapter

- Alignment eyewear is an option for use with visible beams and gives partial visibility for beam observation from diffuse or attenuated reflections, but not full protection from the direct beam.  Use of alignment eyewear will be limited to situations where exposure to a direct beam is prevented, and thorough justification for the use of alignment eyewear must be provided by the laser user.  This must be specifically stated as part of an AHD and approved by the LSO.  Approval for the use of alignment eyewear must be renewed annually, based on an evaluation of the experimental conditions by the LSO.  The following criteria will be used as guidance in determining whether alignment eyewear is appropriate for particular circumstances, and for selecting the appropriate eyewear OD*:
- protection from exposure to the direct beam provided by beam blocks and/or enclosures
- alignment eyewear providing protection from stray reflections from uncoated surfaces, typically ~4% of the direct beam.  OD reduction ~1.4
- alignment eyewear providing protection from diffuse scatter at >0.5m observation distance. OD reduction ~4-5
- attenuation of direct beam ***below*** Class 3b level
- * determination of the appropriate OD (and justification) must be made for specific circumstances by the laser user in consultation with the LSO.

## Summary

- Users need to know limitations of alignment eyewear
- LSO needs to understand limitations of alignment eyewear
- Alignment eyewear has a place in the LSO toolbox
- The LSO needs to approve the use and purchase of laser alignment eyewear
- Comments please
- kbarat@lbl.gov