PHTN1400: Principles Of Laser Systems
Laser Safety (2017W)

Introduction

This is a two-hour lab in which students will investigate the concepts of the Nominal Hazard Zone (NHZ), Optical Density (OD) as it applies to safety glasses, and safety concerns around green laser pointers which involve multiple wavelengths (the same concepts apply to a variety of solid-state laser systems).

BEFORE this lab ...

You must have successfully completed both the Laser Safety Quiz on Blackboard (certifying that you have seen the video and understand the basic safety procedures required in our lab) as well as the Safety Glasses Quiz in lab #0. Both quizzes should have been completed last week.

If a student shows-up to the lab WITHOUT successfully completed quizzes, he/she will be DENIED entrance to the lab, will be marked absent (with a 5% penalty on the total mark in the course), and placed on COURSE CONDITION (in which case you will be expelled if you fail to successfully complete both before the next lab period).

There is no negotiating safety requirements, period.


Prelab (To be done prior to the lab, due upon entry)

    Submission:
  1. Calculate, showing ALL work, the OD required for safety glasses suitable for use with the 1 Watt, 445nm laser used in this lab.
  2. Using the OD you determined for question 1, determine which of the six lenses listed in part B of the lab will work to protect against this laser. List the letter code of the glasses and the OD listed at 445nm.
  3. First, read NIST technical bulletin number 1668 on the dangers of green laser pointers. Truth is, we have a laser pointer bought off a popular bidding site (with free shipping nonetheless) with an output which reads 41mW of total power output and 4mW of green (isolated using a dielectric filter which passes 532nm but blocks all other wavelengths). The 4mW measurement is accurate since the meter was set for "532nm" and the filter effectively blocks all other wavelengths. The 41mW measurement is a complete approximation and is not accurate since the silicon meter used was specific to wavelength and the incoming beam was not spectrally "pure" by any means! Assuming a laser pointer follows the same relative distribution of the pointer in figure 4 of the bulletin (and basing all actual powers against the accurately measured 4mW green output):
    1. Determine the expected power, in mW, of each component (three components, with three different wavelengths) using the ratios from the reading.
    2. Calculate the OD required to protect against each of the three wavelengths (You may assume that the MPE at 808nm is the same as that at 840nm). State the source of the MPE's used (chart, and source, or EasyHaz as shown in lectures).
    3. Find at least TWO lenses from NOIR LaserShields which will protect against this laser pointer properly. List the lens (three letter) code and the OD of the safety glasses at each of the three wavelengths.
    (As you can clearly see, this laser pointer with a 4mW green output looks as if it is a class 3R pointer but when the IR outputs are taken into account, the pointer is really a class 3B and is considerably more dangerous)

The prelab assignment is worth 10% of the total lab mark and is due at the beginning of the lab period. Late marks are not assigned if the prelab is not received at the beginning of the lab: you lose 10% of the total lab marks immediately with no recourse if it is not received upon entering the lab (extensions will NOT be given to "print it out" in the lab ... be prepared with the hardcopy already printed).

Part A: Determining NHZ

Part B. Eyewear OD and Wavelength

Part C. Green Laser Pointer Hazards

Laser Safety Concepts

A review of the key concepts from the lectures as employed in this lab ...

  1. Class I-IV laser definitions and safety requirements for each

  2. Exposure limits (MPE)

  3. Defining Nominal hazard zones (NHZ) and use of barriers

  4. Calculating OD for safety glasses

Part D: (Homework) Evaluating Hazards for Various Lasers

Here are the warning labels of various laser in the lab which you will use in this course. Key parameters such as wavelength and power (required to chose safety glasses properly) are found on these labels (which, by law, are required for all lasers). Some labels are from older lasers and so may feature different information for the current standard.

I-90 Laser Warning Label Coherent Innova-90 Argon-ion laser operating at visible wavelengths. See the Fundamentals text by Csele for exact wavelengths.
Lee YAG Laser Warning Label Lee Lasers Q-Switched YAG laser. As a Q-Switched laser, the MPE is diferent than that for a CW laser and requires, for accuracy, knowledge of pulse duration and pulse rate (usually from the manufacturer or an SOP). The exact model is an LDP-50MQ - it may be converted to 532nm output as well however is currently operating only at 1064nm.
MPB CO2 Laser Warning Label MPB IN-100 CO2 Laser.
Uniphase HeNe Laser Warning Label Uniphase HeNe Laser.

You'll also need a chart of MPE values to begin ... (from ANSI regulations)

For homework, compute, both manually (showing all calculations for required OD) and using EasyHaz software, the required OD for each of these lasers, producing a summary table as follows: Laser Type, Operating wavelength, Power Output, MPE (from OSHA regs), Exposure time (from OSHA regs), Required OD (manually calculated), Required OD (EasyHaz). This is required for the lab submission question 4c.

Lab Report

Hand In a WORD PROCESSED (not handwritten) lab report with contents as outlined below.

Lab Report The FIRST PAGE must be a title page containing nothing more than the title of the lab, the course, and the student's name and ID number

Answer each question as "1", "2", etc with each new question starting on a NEW PAGE so that question 2 starts on the top of a new page and question 3 starts at the top of a different page, etc. Where a question has multiple parts (e.g. 3a, 3b, 3c ...) answer each in a separate paragraph with a title identifying the question in the form "3a., 3b., 3c. ...". Do NOT answer an entire question (e.g. question 3) as a single paragraph.

Questions must be identified at the top of the page as QUESTION 1, QUESTION 2, etc. as shown to the left

This format will assist you in ensuring EACH and EVERY question is answered since marks cannot be given for work not completed, nor would it be expected that you could complete the TEST QUESTIONS which will most certainly be similar to those you see here! (Hint !)

The lab must be submitted in a report cover (preferably either a three-hole punched cover or one with a clamp on the left side, not a binder), and NEVER as a stapled mass of loose papers!

Failure to follow this simple format, used for all condensed labs in this course, will result in deduction of marks

For ALL CALCULATIONS, work must be shown! Answers without calculations will receive a mark of ZERO. Where a calculation is repeated many times (e.g. to complete a table of values) show ONE complete set of example calculations.

LAB SUBMISSION:

    Laser Safety I: NHZ
  1. Hand-in a plot of diffused power readings vs. distance from the target both experimentally (measured in the lab) and theoretically (calculated using the R-squared law as discussed in the procedures above). Show the formula you used to compute the theoretical powers.
  2. Hand-in a calculation of the NHZ for the 445nm laser in part A using the measured power (in the same method as outlined in lectures). Show calculations.
  3. Hand-in a screen-shot of the EasyHaz software output (complete and intact - Try "File > Print" from your browser) showing the NHZ prediction from the software. Be sure to use the newest version of the online software (i.e. 2014 version or newer). Use the same parameters as actually observed in the lab (e.g. actual incident laser power used as read from the laser power meter), not the power rating from the warning label as would usually be used for "worst case" computations and may be wrong regardless.

  4. Laser Safety II: Safety Glass OD
  5. Hand-in the following from part D of the lab:
  6. A summary table from part B of the lab showing evaluation of OD for each lens in the lab (i.e. the OD determined for each lens experimentally). Show one example calculation (one with an OD > 0 but less than infinity). Each table (one per lens is required) will have five columns. These observations will be marked for accuracy so hopefully you followed the procedure carefully.
  7. A summary chart showing the suitability of each lens tested for each of the four lasers from the end of the lab. Put each of the four lasers in Part D (e.g. argon-ion) as a row in the chart, and each of the six lenses in Part B as a column with "S" in intersecting boxes showing suitability. Use the OD as stated directly on each lens (or from the NOIR website) for this chart, not the OD determined in this lab.

  8. Laser Safety III: Regulatory Compliance
  9. Present results for the green laser pointer, outlining (for each laser tested) the combined output power, and power of each component (with an explanation and example calculation of how this was found knowing that the blocking filters used will attenuate and so not transmit 100% - you must calculate the actual power of each component emitted from the laser, not just that read from the meter and include a table of power measurements as outlined in the procedure in the lab above) - Show calculations. Explain as well, for each pointer, if it is compliant with class IIIa limits or not and if not, explain precisely and mathematically why (determine the allowable limits for each wavelength component first).

  10. Laser Safety IV: Application
  11. A CW YAG laser has an output of 20W at 1064nm and 8W at 532nm - both wavelengths are accessible by the user. Find ALL safety glasses (mention both the lens code, for example "YG2", and the stated OD at each wavelength 532nm and 1064nm) from NOIR which will adequately protect against this laser. You must list at least FIVE glasses which work for this laser. ORDER these from highest VLT to lowest (since higher VLT is desirable, assuming protection is adequate). Obviously you must compute the required OD at each wavelength first - SHOW this BEFORE the table outlining the lenses found (including calculations if computed manually).
  12. The same laser as above is pumped by a large semiconductor laser diode array (50W total) at 808nm. Assuming you are working on the laser with the cover open and so all three wavelengths (808, 1064, and 532) are accessible, find ALL safety glasses which protect against this laser (there are more than one which work). Again, begin by outlining the OD required at 808nm then the table of lenses with lens code and OD at three wavelengths of interest (532 nm, 808 nm, and 1064 nm)
  13. Calculate the required OD, and then find at least three safety glasses suitable for our Lee LDP-20MQG laser operating at 532nm. Specifications of this Q-switched pulsed laser may be found on the SOP area of the technology web site. Show how you determined MPE and OD for this laser first, then list the lenses along with the stated OD for each at 532nm.