Laser Safety and Alignment in the laboratory

[Stephen Bunnell]

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Dear all,

    Although I do a good deal of imaging, I'm a biologist by training, and
have little familiarity with the installation and alignment of lasers and
with the pertinent safety considerations. I'd like to change this,
especially since I have a dead Kr/Ar laser on a 3-laser 5-line launch that
uses an AOTF and feeds a single fiber. This laser is heavily used to provide
both 568 and 643 lines, but is pretty weak, at ~15mW per line.

    Ideally, I'd like to replace the laser with more powerful diode-based
lasers, but the laser platform is a custom job, and I am not comfortable
drilling into it to create new mounting positions. I get the feeling that it
would be rather expensive to migrate all the viable components to a new
platform and replace the Kr/Ar with diode lasers. Alternately, I could get
the laser refurbished (a steal, at ~$2000), but then I'd still face the
dismounting, remounting, and alignment of the laser. I am not currently
comfortable with the alignment and safety aspects of such an installation.
I'm looking for guidance on how to learn these skills. Is this the kind of
thing one can learn by doing, or do I need expert guidance? If I'm going to
start doing my own laser installation and alignment (and I think that I
should), what training and safety kit should I be getting? Where might I get
the relevant training?

    Thanks much,

    Steve
   



****************************************************************************
Stephen C. Bunnell, Ph.D.
Assistant Professor
Tufts University Medical School
Department of Pathology
Jaharis Bldg., Room 512
150 Harrison Ave.
Boston, MA 02111

Phone: [phone]
Fax:   [phone]
Email: [hidden email]

[John Oreopoulos]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

Stephan,

The first thing you'll definitely want to do is get some basic laser training for you and all members of your laboratory who would be involved in any laser beam alignment. Some universities now provide laser safety training courses in addition to the usual annual general lab safety courses. The notes and materials of one such laser safety course can be found here:

http://www.ehs.utoronto.ca/services/laserpg/laserhome.htm

Here is one specific page on good alignment practices:

http://www.ehs.utoronto.ca/Assets/ehs+Digital+Assets/ehs3/laserpg/beam+alignment.pdf

When I was at the University of Toronto, the laser safety program was still relatively new, and the person in charge for all university laser safety had to actively seek out labs using lasers or wait for labs to seek him out because there was no master list of which research labs had these kinds of tools and getting the word out about the course was difficult. Ask around at your university and find out if such a course exists there.

As for rigging your own lasers into a laser combiner system for a confocal microscope, it can be done if you understand the combiner architecture and use sturdy mounts that have good stability and provide the right degrees of freedom for movement. Sometimes you'll find clear windows held in rotating mounts for each laser that act as fine adjustment beam shifters inside the combiner. Coupling laser light into the optical fiber that eventually connects to the confocal scan head can be quite frustrating and requires patience and practice. There is a systematic way to "walk" the laser beam into the right alignment, but only the technical representatives of your microscope maker or laser combiner will know that specific procedure.

The other thing you should recognize is that the dichoric mirrors present in the laser combiners are usually designed for a specific laser wavelength. If the laser you're replacing is not of the same wavelength, you'll need to find out what the characteristics of the dichroics the laser beam is interacting with (transmission or reflection) are, otherwise you could lose a significant amount of light down the path. (If you can't get that specific information, just feed the laser beam through or reflect the beam off the mirror and measure the laser power before and after the mirror with a laser power meter to find out if the laser wavelength and mirror are compatible. You should expect 80-95% transmission or reflection).

Finally, many laser scanning confocal microscope laser combiners use a polarization maintaining (PM) optical fiber to deliver light to the scan head and maximize light throughput, meaning that the fiber expects the incoming laser light to have a specific polarization orientation. If the polarization angle of your laser is orthogonal to the PM fiber axis, then you will have very little light coming out the exit end of the fiber. Usually this fiber orientation is vertical or horizontal with respect to the combiner base. Cylindrical HeNe lasers on older comber systems can be rotated in their mount to satisfy this condition, but this is not the case for small cubic diode based lasers. If when mounted to a base the diode laser does not have the same polarization orientation as the optical fiber mount in the combiner, you could insert some polarization rotating optics (half-wave plates) into the beam, but the custom mounts will become more complicated. Alternatively, if the polarization angle of the diode laser is vertical or horizontal with respect to the base of the laser (this information can be found on the laser makers website, or you can test it yourself with a polarizer / sheet of polaroid film), you could mount it 90 degrees on it's side with respect to the combiner.

Unfortunately I don't have much experience with the alignment of beams through AOTFs, but I know these devices also expect a certain laser polarization and they will have to be "tuned" if the new laser does not have the same wavelength as the old one being replaced.

There may be other aspects associated with this whole process that I'm still not aware of or familiar with. For example, I can't tell you what power laser beam you should buy on your own (20 mW? 50 mW? 100 mW or higher?). I also recently learned that if high power lasers are to be coupled into such a system, it's possible the optical fiber can be damaged in the alignment process.

The bottom line is, before you go out and experiment with this (after you've been certified by a laser safety training course), make sure you're not violating any service contracts with your microscope maker (if you have one). Perhaps you could buy the lasers yourself and ask ahead of time if your microscope provider would be willing to help you with the installation and save you some down time.

Good luck!

> John Oreopoulos
> Research Assistant
> Spectral Applied Research
> 9078 Leslie Street, Unit 11
> Richmond Hill
> Ontario, Canada


On 2010-11-19, at 5:07 PM, Stephen Bunnell wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Dear all,
>
>    Although I do a good deal of imaging, I'm a biologist by training, and
> have little familiarity with the installation and alignment of lasers and
> with the pertinent safety considerations. I'd like to change this,
> especially since I have a dead Kr/Ar laser on a 3-laser 5-line launch that
> uses an AOTF and feeds a single fiber. This laser is heavily used to provide
> both 568 and 643 lines, but is pretty weak, at ~15mW per line.
>
>    Ideally, I'd like to replace the laser with more powerful diode-based
> lasers, but the laser platform is a custom job, and I am not comfortable
> drilling into it to create new mounting positions. I get the feeling that it
> would be rather expensive to migrate all the viable components to a new
> platform and replace the Kr/Ar with diode lasers. Alternately, I could get
> the laser refurbished (a steal, at ~$2000), but then I'd still face the
> dismounting, remounting, and alignment of the laser. I am not currently
> comfortable with the alignment and safety aspects of such an installation.
> I'm looking for guidance on how to learn these skills. Is this the kind of
> thing one can learn by doing, or do I need expert guidance? If I'm going to
> start doing my own laser installation and alignment (and I think that I
> should), what training and safety kit should I be getting? Where might I get
> the relevant training?
>
>    Thanks much,
>
>    Steve
>
>
>
>
> ****************************************************************************
> Stephen C. Bunnell, Ph.D.
> Assistant Professor
> Tufts University Medical School
> Department of Pathology
> Jaharis Bldg., Room 512
> 150 Harrison Ave.
> Boston, MA 02111
>
> Phone: [phone]
> Fax:   [phone]
> Email: [hidden email]

[James Thieman]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

Steve,

A simple resource for laser safety with some great examples including
calculations can be found at Sam's Laser FAQ:

http://repairfaq.ece.drexel.edu/sam/lasersaf.htm#safcils

You may have already found it with a simple google search.

Jake Thieman


Graduate Student
University of Pittsburgh
Department of Cell Biology
S306 Biomedical Science Tower
3500 Terrace St.
Pittsburgh, PA 15261
412-648-9713

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Stephan,
>
> The first thing you'll definitely want to do is get some basic laser
> training for you and all members of your laboratory who would be involved
> in any laser beam alignment. Some universities now provide laser safety
> training courses in addition to the usual annual general lab safety
> courses. The notes and materials of one such laser safety course can be
> found here:
>
> http://www.ehs.utoronto.ca/services/laserpg/laserhome.htm
>
> Here is one specific page on good alignment practices:
>
> http://www.ehs.utoronto.ca/Assets/ehs+Digital+Assets/ehs3/laserpg/beam+alignment.pdf
>
> When I was at the University of Toronto, the laser safety program was
> still relatively new, and the person in charge for all university laser
> safety had to actively seek out labs using lasers or wait for labs to seek
> him out because there was no master list of which research labs had these
> kinds of tools and getting the word out about the course was difficult.
> Ask around at your university and find out if such a course exists there.
>
> As for rigging your own lasers into a laser combiner system for a confocal
> microscope, it can be done if you understand the combiner architecture and
> use sturdy mounts that have good stability and provide the right degrees
> of freedom for movement. Sometimes you'll find clear windows held in
> rotating mounts for each laser that act as fine adjustment beam shifters
> inside the combiner. Coupling laser light into the optical fiber that
> eventually connects to the confocal scan head can be quite frustrating and
> requires patience and practice. There is a systematic way to "walk" the
> laser beam into the right alignment, but only the technical
> representatives of your microscope maker or laser combiner will know that
> specific procedure.
>
> The other thing you should recognize is that the dichoric mirrors present
> in the laser combiners are usually designed for a specific laser
> wavelength. If the laser you're replacing is not of the same wavelength,
> you'll need to find out what the characteristics of the dichroics the
> laser beam is interacting with (transmission or reflection) are, otherwise
> you could lose a significant amount of light down the path. (If you can't
> get that specific information, just feed the laser beam through or reflect
> the beam off the mirror and measure the laser power before and after the
> mirror with a laser power meter to find out if the laser wavelength and
> mirror are compatible. You should expect 80-95% transmission or
> reflection).
>
> Finally, many laser scanning confocal microscope laser combiners use a
> polarization maintaining (PM) optical fiber to deliver light to the scan
> head and maximize light throughput, meaning that the fiber expects the
> incoming laser light to have a specific polarization orientation. If the
> polarization angle of your laser is orthogonal to the PM fiber axis, then
> you will have very little light coming out the exit end of the fiber.
> Usually this fiber orientation is vertical or horizontal with respect to
> the combiner base. Cylindrical HeNe lasers on older comber systems can be
> rotated in their mount to satisfy this condition, but this is not the case
> for small cubic diode based lasers. If when mounted to a base the diode
> laser does not have the same polarization orientation as the optical fiber
> mount in the combiner, you could insert some polarization rotating optics
> (half-wave plates) into the beam, but the custom mounts will become more
> complicated. Alternatively, if the polarization angle of the diode laser
> is vertical or horizontal with respect to the base of the laser (this
> information can be found on the laser makers website, or you can test it
> yourself with a polarizer / sheet of polaroid film), you could mount it 90
> degrees on it's side with respect to the combiner.
>
> Unfortunately I don't have much experience with the alignment of beams
> through AOTFs, but I know these devices also expect a certain laser
> polarization and they will have to be "tuned" if the new laser does not
> have the same wavelength as the old one being replaced.
>
> There may be other aspects associated with this whole process that I'm
> still not aware of or familiar with. For example, I can't tell you what
> power laser beam you should buy on your own (20 mW? 50 mW? 100 mW or
> higher?). I also recently learned that if high power lasers are to be
> coupled into such a system, it's possible the optical fiber can be damaged
> in the alignment process.
>
> The bottom line is, before you go out and experiment with this (after
> you've been certified by a laser safety training course), make sure you're
> not violating any service contracts with your microscope maker (if you
> have one). Perhaps you could buy the lasers yourself and ask ahead of time
> if your microscope provider would be willing to help you with the
> installation and save you some down time.
>
> Good luck!
>
>> John Oreopoulos
>> Research Assistant
>> Spectral Applied Research
>> 9078 Leslie Street, Unit 11
>> Richmond Hill
>> Ontario, Canada
>
>
> On 2010-11-19, at 5:07 PM, Stephen Bunnell wrote:
>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>> *****
>>
>> Dear all,
>>
>>    Although I do a good deal of imaging, I'm a biologist by training,
>> and
>> have little familiarity with the installation and alignment of lasers
>> and
>> with the pertinent safety considerations. I'd like to change this,
>> especially since I have a dead Kr/Ar laser on a 3-laser 5-line launch
>> that
>> uses an AOTF and feeds a single fiber. This laser is heavily used to
>> provide
>> both 568 and 643 lines, but is pretty weak, at ~15mW per line.
>>
>>    Ideally, I'd like to replace the laser with more powerful diode-based
>> lasers, but the laser platform is a custom job, and I am not comfortable
>> drilling into it to create new mounting positions. I get the feeling
>> that it
>> would be rather expensive to migrate all the viable components to a new
>> platform and replace the Kr/Ar with diode lasers. Alternately, I could
>> get
>> the laser refurbished (a steal, at ~$2000), but then I'd still face the
>> dismounting, remounting, and alignment of the laser. I am not currently
>> comfortable with the alignment and safety aspects of such an
>> installation.
>> I'm looking for guidance on how to learn these skills. Is this the kind
>> of
>> thing one can learn by doing, or do I need expert guidance? If I'm going
>> to
>> start doing my own laser installation and alignment (and I think that I
>> should), what training and safety kit should I be getting? Where might I
>> get
>> the relevant training?
>>
>>    Thanks much,
>>
>>    Steve
>>
>>
>>
>>
>> ****************************************************************************
>> Stephen C. Bunnell, Ph.D.
>> Assistant Professor
>> Tufts University Medical School
>> Department of Pathology
>> Jaharis Bldg., Room 512
>> 150 Harrison Ave.
>> Boston, MA 02111
>>
>> Phone: [phone]
>> Fax:   [phone]
>> Email: [hidden email]
>