Laser power meter and sensor

[Martin Seem]

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A couple of questions for the list:

1, We are currently in the process of buying a new laser power meter that will
primarily be used to check the general stability and power output of the laser
lines of our CLSMs. Have anybody recently bought a power meter after
considering some of currently offered products (like the Coherent LabMax
TOP, Newport 1918-R, GigaHertz PT-9610 and Ophir Vega). Which one did
you choose and why?

2, Are there any commercially available laser meter sensors that will allow us
to measure the actual laser light output from a high NA (NA>1) water or oil
immersion objective?

Martin

[Johannes Helm]

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> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> A couple of questions for the list:
>
> 1, We are currently in the process of buying a new laser power meter that
> will
> primarily be used to check the general stability and power output of the
> laser
> lines of our CLSMs. Have anybody recently bought a power meter after
> considering some of currently offered products (like the Coherent LabMax
> TOP, Newport 1918-R, GigaHertz PT-9610 and Ophir Vega). Which one did
> you choose and why?

Good afternoon, Martin,

we have some by Coherent, Melles Griot, Standa, Spectra Physics...
Fine all (and some are OEM products just having received a selling
company's label). If you want to record the laser power over long periods
of time, it might be a good idea to check that your measurement amplifier
provides a BNC cabled output, which you can feed into a recorder (LabView
device or something like that).

>
> 2, Are there any commercially available laser meter sensors that will
> allow us
> to measure the actual laser light output from a high NA (NA>1) water or
> oil
> immersion objective?

Coherent "Laser Check". Fine device, indeed! Always make sure you adjust
it for the proper wavelength. The versions I have are not suitable for
lambda<400nm.

NOTE! When you measure the power in the focal region of any immersion
objective, you should

a)
Assume that the immersion medium does not absorb a noticeable faction of
the power (if it does, then it is "bio-dirty" with non dissolved particles
or with small air bubbles, and it should not be, not even for biological
measurements),

b)
Make sure the objective front lens really is clean and wiped for the power
measurement.

Concerning b): It is, to my mind, not a good idea to put any water or oil
between the objective front lens and the detector unit. It just soils the
detector unit and, given a), should not make any difference. However, if
you have some rest drops of oil or water on the objective but at the same
time do NOT establish an immersion like contact to the detector, then you
will lose a considerable amount of power due to the reflection of light at
the surface oil-air or water-air at the lower ends of the drops.


Best wishes,

Johannes


>
> Martin
>


--
P. Johannes Helm

Voice: ([phone] (office)
Fax: [phone] (office)

[John Oreopoulos]

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Hi Martin, it regards to question 2, I don't think such a power meter exists (although if someone else knows otherwise, I'd love to know as well). You're better off measuring the power at the back of the objective (ie: unscrew the objective and measure the power at the empty nosepiece), and then use the wavelength transmission curve of the objective (usually available from the manufacturer) to calculate the percentage of light that gets through to the front end of the objective - some error is introduced here as there is some variability in the transmission for each identical objective, but at least you get a good estimate of the actual power on the other side of the objective.

You might also consider over what area that power that gets to the other side of the objective is projected to determine the power density (power per unit area), which is is a more relevant parameter. There is a nice Nature Protocols paper from 2008 that talks about these kinds of measurements, and there is mention about choice of power meter I think:

Grunwald, D., et al., Calibrating excitation light fluxes for quantitative light microscopy in cell biology. Nature Protocols, 2008. 3(11): p. 1809-1814.

Cheers,

John Oreopoulos
Staff Scientist
Spectral Applied Research
Richmond Hill, Ontario
Canada
www.spectral.ca


On 2013-03-12, at 11:17 AM, Martin Seem wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> A couple of questions for the list:
>
> 1, We are currently in the process of buying a new laser power meter that will
> primarily be used to check the general stability and power output of the laser
> lines of our CLSMs. Have anybody recently bought a power meter after
> considering some of currently offered products (like the Coherent LabMax
> TOP, Newport 1918-R, GigaHertz PT-9610 and Ophir Vega). Which one did
> you choose and why?
>
> 2, Are there any commercially available laser meter sensors that will allow us
> to measure the actual laser light output from a high NA (NA>1) water or oil
> immersion objective?
>
> Martin

[Julio Vazquez]

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You can check this:

http://www.ldgi-xcite.com/products-xr2100-xp750.php

We use a similar meter from Coherent, but i'm not in the lab now and can't tell you the model #.  We routinely use power at the focal plane with up to 20x objectives. Not sure how accurate it would be with high NA… depends on how close you can get to the objective…

Julio Vazquez.


----- Original Message -----
From: "John Oreopoulos" <[hidden email]>
To: [hidden email]
Sent: Tuesday, March 12, 2013 9:09:35 AM
Subject: Re: Laser power meter and sensor

*****
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Hi Martin, it regards to question 2, I don't think such a power meter exists (although if someone else knows otherwise, I'd love to know as well). You're better off measuring the power at the back of the objective (ie: unscrew the objective and measure the power at the empty nosepiece), and then use the wavelength transmission curve of the objective (usually available from the manufacturer) to calculate the percentage of light that gets through to the front end of the objective - some error is introduced here as there is some variability in the transmission for each identical objective, but at least you get a good estimate of the actual power on the other side of the objective.

You might also consider over what area that power that gets to the other side of the objective is projected to determine the power density (power per unit area), which is is a more relevant parameter. There is a nice Nature Protocols paper from 2008 that talks about these kinds of measurements, and there is mention about choice of power meter I think:

Grunwald, D., et al., Calibrating excitation light fluxes for quantitative light microscopy in cell biology. Nature Protocols, 2008. 3(11): p. 1809-1814.

Cheers,

John Oreopoulos
Staff Scientist
Spectral Applied Research
Richmond Hill, Ontario
Canada
www.spectral.ca


On 2013-03-12, at 11:17 AM, Martin Seem wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> A couple of questions for the list:
>
> 1, We are currently in the process of buying a new laser power meter that will
> primarily be used to check the general stability and power output of the laser
> lines of our CLSMs. Have anybody recently bought a power meter after
> considering some of currently offered products (like the Coherent LabMax
> TOP, Newport 1918-R, GigaHertz PT-9610 and Ophir Vega). Which one did
> you choose and why?
>
> 2, Are there any commercially available laser meter sensors that will allow us
> to measure the actual laser light output from a high NA (NA>1) water or oil
> immersion objective?
>
> Martin

[John Oreopoulos]

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Julio, on the specifications tab of the weblink you sent, it says regarding objective compatibility:

4X-63X; air coupled, with FOV diameters less than 10mm

Just to re-iterate, I don't think you can use an immersion objective with a power meter like this (someone from Lumen Dynamics can confirm this). Not only would it require you to place the optical sensor in contact with the immersion fluid of the objective (which might damage it), but even if you could do that, it still wouldn't work because these devices have a low acceptance angle for light, that is to say, these devices won't capture/register the light that approaches the sensor at very oblique angles which are typically present when using high NA immersion objectives.

The absence of the immersion medium is also not an option because then many of the oblique rays will be lost at the front lens due to total internal reflection at the glass-air interface.

John Oreopoulos


On 2013-03-12, at 12:38 PM, Vazquez Lopez, Julio wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> You can check this:
>
> http://www.ldgi-xcite.com/products-xr2100-xp750.php
>
> We use a similar meter from Coherent, but i'm not in the lab now and can't tell you the model #.  We routinely use power at the focal plane with up to 20x objectives. Not sure how accurate it would be with high NA… depends on how close you can get to the objective…
>
> Julio Vazquez.
>
>
> ----- Original Message -----
> From: "John Oreopoulos" <[hidden email]>
> To: [hidden email]
> Sent: Tuesday, March 12, 2013 9:09:35 AM
> Subject: Re: Laser power meter and sensor
>
> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Hi Martin, it regards to question 2, I don't think such a power meter exists (although if someone else knows otherwise, I'd love to know as well). You're better off measuring the power at the back of the objective (ie: unscrew the objective and measure the power at the empty nosepiece), and then use the wavelength transmission curve of the objective (usually available from the manufacturer) to calculate the percentage of light that gets through to the front end of the objective - some error is introduced here as there is some variability in the transmission for each identical objective, but at least you get a good estimate of the actual power on the other side of the objective.
>
> You might also consider over what area that power that gets to the other side of the objective is projected to determine the power density (power per unit area), which is is a more relevant parameter. There is a nice Nature Protocols paper from 2008 that talks about these kinds of measurements, and there is mention about choice of power meter I think:
>
> Grunwald, D., et al., Calibrating excitation light fluxes for quantitative light microscopy in cell biology. Nature Protocols, 2008. 3(11): p. 1809-1814.
>
> Cheers,
>
> John Oreopoulos
> Staff Scientist
> Spectral Applied Research
> Richmond Hill, Ontario
> Canada
> www.spectral.ca
>
>
> On 2013-03-12, at 11:17 AM, Martin Seem wrote:
>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>> *****
>>
>> A couple of questions for the list:
>>
>> 1, We are currently in the process of buying a new laser power meter that will
>> primarily be used to check the general stability and power output of the laser
>> lines of our CLSMs. Have anybody recently bought a power meter after
>> considering some of currently offered products (like the Coherent LabMax
>> TOP, Newport 1918-R, GigaHertz PT-9610 and Ophir Vega). Which one did
>> you choose and why?
>>
>> 2, Are there any commercially available laser meter sensors that will allow us
>> to measure the actual laser light output from a high NA (NA>1) water or oil
>> immersion objective?
>>
>> Martin

[Julio Vazquez]

*****
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http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
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I wasn't suggesting to use immersion oil on the power meter sensor, and I don't know how those things are engineered… although I'm guessing a coevrslip-like protective window in front of the sensor could take care of that problem.

However, measuring the power at the nosepiece seems more complicated to me, and then I would have no way to know which fraction of that power actually enters the objective…. For instance, we have two objectives from the same vendor with the same specs (63/1.4 Plan Apo) which have back apertures of different sizes (and one therefore delivers more light to the focal plane, all other thing being equal).

On the other hand, if the power meter sensor is fairly large and is held pretty close to the front element of the lens, I suspect the error due to rays that miss the sensor (i.e rays at close to 180 degrees, would be pretty small… certainly smaller in my opinion to the error in estimating how much light coming out of the nosepiece actually enters the objective.

Julio.

 

----- Original Message -----
From: "John Oreopoulos" <[hidden email]>
To: [hidden email]
Sent: Tuesday, March 12, 2013 10:04:08 AM
Subject: Re: Laser power meter and sensor

*****
To join, leave or search the confocal microscopy listserv, go to:
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*****

Julio, on the specifications tab of the weblink you sent, it says regarding objective compatibility:

4X-63X; air coupled, with FOV diameters less than 10mm

Just to re-iterate, I don't think you can use an immersion objective with a power meter like this (someone from Lumen Dynamics can confirm this). Not only would it require you to place the optical sensor in contact with the immersion fluid of the objective (which might damage it), but even if you could do that, it still wouldn't work because these devices have a low acceptance angle for light, that is to say, these devices won't capture/register the light that approaches the sensor at very oblique angles which are typically present when using high NA immersion objectives.

The absence of the immersion medium is also not an option because then many of the oblique rays will be lost at the front lens due to total internal reflection at the glass-air interface.

John Oreopoulos


On 2013-03-12, at 12:38 PM, Vazquez Lopez, Julio wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> You can check this:
>
> http://www.ldgi-xcite.com/products-xr2100-xp750.php
>
> We use a similar meter from Coherent, but i'm not in the lab now and can't tell you the model #.  We routinely use power at the focal plane with up to 20x objectives. Not sure how accurate it would be with high NA… depends on how close you can get to the objective…
>
> Julio Vazquez.
>
>
> ----- Original Message -----
> From: "John Oreopoulos" <[hidden email]>
> To: [hidden email]
> Sent: Tuesday, March 12, 2013 9:09:35 AM
> Subject: Re: Laser power meter and sensor
>
> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Hi Martin, it regards to question 2, I don't think such a power meter exists (although if someone else knows otherwise, I'd love to know as well). You're better off measuring the power at the back of the objective (ie: unscrew the objective and measure the power at the empty nosepiece), and then use the wavelength transmission curve of the objective (usually available from the manufacturer) to calculate the percentage of light that gets through to the front end of the objective - some error is introduced here as there is some variability in the transmission for each identical objective, but at least you get a good estimate of the actual power on the other side of the objective.
>
> You might also consider over what area that power that gets to the other side of the objective is projected to determine the power density (power per unit area), which is is a more relevant parameter. There is a nice Nature Protocols paper from 2008 that talks about these kinds of measurements, and there is mention about choice of power meter I think:
>
> Grunwald, D., et al., Calibrating excitation light fluxes for quantitative light microscopy in cell biology. Nature Protocols, 2008. 3(11): p. 1809-1814.
>
> Cheers,
>
> John Oreopoulos
> Staff Scientist
> Spectral Applied Research
> Richmond Hill, Ontario
> Canada
> www.spectral.ca
>
>
> On 2013-03-12, at 11:17 AM, Martin Seem wrote:
>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>> *****
>>
>> A couple of questions for the list:
>>
>> 1, We are currently in the process of buying a new laser power meter that will
>> primarily be used to check the general stability and power output of the laser
>> lines of our CLSMs. Have anybody recently bought a power meter after
>> considering some of currently offered products (like the Coherent LabMax
>> TOP, Newport 1918-R, GigaHertz PT-9610 and Ophir Vega). Which one did
>> you choose and why?
>>
>> 2, Are there any commercially available laser meter sensors that will allow us
>> to measure the actual laser light output from a high NA (NA>1) water or oil
>> immersion objective?
>>
>> Martin

[Glen MacDonald-2]

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Low NA lenses reduce reflections by high incident angles and their long working distances provide tolerant focus.  Just keep the focus spot less than the diameter of the detector area.  
transmission efficiency can be estimated by focusing the measured objective and on an immersion objective on a clean cover slipped slide with Koehler illumination adjusted.  then measure the mean intensity of a bright field image from each lens.  You might have to place a ND filter to avoid saturation.   If you want to be picky about wavelengths, perhaps place color filters in the light path.  

I'm using a Thorlabs USB power meter, which can record time-lapse measurements with user-adjustable averaging.

Glen MacDonald
        Core for Communication Research
Virginia Merrill Bloedel Hearing Research Center
        Cellular Morphology Core
Center on Human Development and Disability
Box 357923
University of Washington
Seattle, WA 98195-7923  USA
[phone]
[hidden email]
[hidden email]





On Mar 12, 2013, at 10:04 AM, John Oreopoulos <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Julio, on the specifications tab of the weblink you sent, it says regarding objective compatibility:
>
> 4X-63X; air coupled, with FOV diameters less than 10mm
>
> Just to re-iterate, I don't think you can use an immersion objective with a power meter like this (someone from Lumen Dynamics can confirm this). Not only would it require you to place the optical sensor in contact with the immersion fluid of the objective (which might damage it), but even if you could do that, it still wouldn't work because these devices have a low acceptance angle for light, that is to say, these devices won't capture/register the light that approaches the sensor at very oblique angles which are typically present when using high NA immersion objectives.
>
> The absence of the immersion medium is also not an option because then many of the oblique rays will be lost at the front lens due to total internal reflection at the glass-air interface.
>
> John Oreopoulos
>
>
> On 2013-03-12, at 12:38 PM, Vazquez Lopez, Julio wrote:
>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>> *****
>>
>> You can check this:
>>
>> http://www.ldgi-xcite.com/products-xr2100-xp750.php
>>
>> We use a similar meter from Coherent, but i'm not in the lab now and can't tell you the model #.  We routinely use power at the focal plane with up to 20x objectives. Not sure how accurate it would be with high NA… depends on how close you can get to the objective…
>>
>> Julio Vazquez.
>>
>>
>> ----- Original Message -----
>> From: "John Oreopoulos" <[hidden email]>
>> To: [hidden email]
>> Sent: Tuesday, March 12, 2013 9:09:35 AM
>> Subject: Re: Laser power meter and sensor
>>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>> *****
>>
>> Hi Martin, it regards to question 2, I don't think such a power meter exists (although if someone else knows otherwise, I'd love to know as well). You're better off measuring the power at the back of the objective (ie: unscrew the objective and measure the power at the empty nosepiece), and then use the wavelength transmission curve of the objective (usually available from the manufacturer) to calculate the percentage of light that gets through to the front end of the objective - some error is introduced here as there is some variability in the transmission for each identical objective, but at least you get a good estimate of the actual power on the other side of the objective.
>>
>> You might also consider over what area that power that gets to the other side of the objective is projected to determine the power density (power per unit area), which is is a more relevant parameter. There is a nice Nature Protocols paper from 2008 that talks about these kinds of measurements, and there is mention about choice of power meter I think:
>>
>> Grunwald, D., et al., Calibrating excitation light fluxes for quantitative light microscopy in cell biology. Nature Protocols, 2008. 3(11): p. 1809-1814.
>>
>> Cheers,
>>
>> John Oreopoulos
>> Staff Scientist
>> Spectral Applied Research
>> Richmond Hill, Ontario
>> Canada
>> www.spectral.ca
>>
>>
>> On 2013-03-12, at 11:17 AM, Martin Seem wrote:
>>
>>> *****
>>> To join, leave or search the confocal microscopy listserv, go to:
>>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>>> *****
>>>
>>> A couple of questions for the list:
>>>
>>> 1, We are currently in the process of buying a new laser power meter that will
>>> primarily be used to check the general stability and power output of the laser
>>> lines of our CLSMs. Have anybody recently bought a power meter after
>>> considering some of currently offered products (like the Coherent LabMax
>>> TOP, Newport 1918-R, GigaHertz PT-9610 and Ophir Vega). Which one did
>>> you choose and why?
>>>
>>> 2, Are there any commercially available laser meter sensors that will allow us
>>> to measure the actual laser light output from a high NA (NA>1) water or oil
>>> immersion objective?
>>>
>>> Martin

[Johannes Helm]

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

> The absence of the immersion medium is also not an option because then
> many of the oblique rays will be lost at the front lens due to total
> internal reflection at the glass-air interface.
>
> John Oreopoulos


That is right, John, but the faction of power, which then is reflected
back into the objective, can be estimated under the pre-assumptions that
you overfill the image side aperture of the objective and that the beam
expansion factor is so large that the power profile measured across the
aperture does not drop "too much" and that the reflective losses inside
the objective are invariant as a function of the radial distance from the
optical axis (which, I admit, is a dared assumption, indeed).


If you have an immersion medium lens for an immersion medium with
refractive index > 1 (in other words: in praxi anything besides air) at NA
> 1, then the light cone from the front lens will be stripped of a "hollow
cone" matching the NA differences between approx. 1.0 and the factual NA
(when using the objective with its proper immersion medium). Given the
focal length of the (immersed) objective and the diameter of the circular
front lens, this will indicate the ring along the edge of the circular
front lens, which is "lost". Calculating the area of that ring and the
area of the front lens and assuming what I had written above, one can
estimate the loss due to the absence of the immersion medium.


Best,
Johannes


--
P. Johannes Helm

Voice: ([phone] (office)
Fax: [phone] (office)

[John Oreopoulos]

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*****

> I wasn't suggesting to use immersion oil on the power meter sensor, and I don't know how those things are engineered
Yeah, my comment about the absence of immersion medium was actually in reference to Johannes email that came a bit after yours where he said it could be done without immersion medium.

> … although I'm guessing a coevrslip-like protective window in front of the sensor could take care of that problem.
But in that case, now you've got a glass-air interface between the coverslip and the sensor. You'll get total internal reflection again. You might lose even more power doing it that way because of multiple reflection interfaces... Unless the coverslip is bonded directly to the sensor material...

> However, measuring the power at the nosepiece seems more complicated to me, and then I would have no way to know which fraction of that power actually enters the objective…. For instance, we have two objectives from the same vendor with the same specs (63/1.4 Plan Apo) which have back apertures of different sizes (and one therefore delivers more light to the focal plane, all other thing being equal).
I think Grunwald's method addresses this point by inserting an adjustable aperture at the nosepiece which can be set to match the back-aperture diameter of the objectives in question.

> On the other hand, if the power meter sensor is fairly large and is held pretty close to the front element of the lens, I suspect the error due to rays that miss the sensor (i.e rays at close to 180 degrees, would be pretty small… certainly smaller in my opinion to the error in estimating how much light coming out of the nosepiece actually enters the objective.

The critical angle for glass-air is somewhere around 45 degrees I think. A high NA oil-immersion objective can easily direct light rays towards a point up to 75 degrees with the oil and the coverslip. I think you'd be a fair chunk of the light in that case (anything between 45 and 75 degrees).

It's a good question though about which method is more accurate. If I had the time, I'd do a comparison between the method described by Grunwald et al and this method of protecting a large sensor power meter with a coverslip. Anyone else out there care to try that? Could make for a nice, short technical paper.

Cheers,

John Oreopoulos




On 2013-03-12, at 2:18 PM, Vazquez Lopez, Julio wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> I wasn't suggesting to use immersion oil on the power meter sensor, and I don't know how those things are engineered… although I'm guessing a coevrslip-like protective window in front of the sensor could take care of that problem.
>
> However, measuring the power at the nosepiece seems more complicated to me, and then I would have no way to know which fraction of that power actually enters the objective…. For instance, we have two objectives from the same vendor with the same specs (63/1.4 Plan Apo) which have back apertures of different sizes (and one therefore delivers more light to the focal plane, all other thing being equal).
>
> On the other hand, if the power meter sensor is fairly large and is held pretty close to the front element of the lens, I suspect the error due to rays that miss the sensor (i.e rays at close to 180 degrees, would be pretty small… certainly smaller in my opinion to the error in estimating how much light coming out of the nosepiece actually enters the objective.
>
> Julio.
>
>
>
> ----- Original Message -----
> From: "John Oreopoulos" <[hidden email]>
> To: [hidden email]
> Sent: Tuesday, March 12, 2013 10:04:08 AM
> Subject: Re: Laser power meter and sensor
>
> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Julio, on the specifications tab of the weblink you sent, it says regarding objective compatibility:
>
> 4X-63X; air coupled, with FOV diameters less than 10mm
>
> Just to re-iterate, I don't think you can use an immersion objective with a power meter like this (someone from Lumen Dynamics can confirm this). Not only would it require you to place the optical sensor in contact with the immersion fluid of the objective (which might damage it), but even if you could do that, it still wouldn't work because these devices have a low acceptance angle for light, that is to say, these devices won't capture/register the light that approaches the sensor at very oblique angles which are typically present when using high NA immersion objectives.
>
> The absence of the immersion medium is also not an option because then many of the oblique rays will be lost at the front lens due to total internal reflection at the glass-air interface.
>
> John Oreopoulos
>
>
> On 2013-03-12, at 12:38 PM, Vazquez Lopez, Julio wrote:
>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>> *****
>>
>> You can check this:
>>
>> http://www.ldgi-xcite.com/products-xr2100-xp750.php
>>
>> We use a similar meter from Coherent, but i'm not in the lab now and can't tell you the model #.  We routinely use power at the focal plane with up to 20x objectives. Not sure how accurate it would be with high NA… depends on how close you can get to the objective…
>>
>> Julio Vazquez.
>>
>>
>> ----- Original Message -----
>> From: "John Oreopoulos" <[hidden email]>
>> To: [hidden email]
>> Sent: Tuesday, March 12, 2013 9:09:35 AM
>> Subject: Re: Laser power meter and sensor
>>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>> *****
>>
>> Hi Martin, it regards to question 2, I don't think such a power meter exists (although if someone else knows otherwise, I'd love to know as well). You're better off measuring the power at the back of the objective (ie: unscrew the objective and measure the power at the empty nosepiece), and then use the wavelength transmission curve of the objective (usually available from the manufacturer) to calculate the percentage of light that gets through to the front end of the objective - some error is introduced here as there is some variability in the transmission for each identical objective, but at least you get a good estimate of the actual power on the other side of the objective.
>>
>> You might also consider over what area that power that gets to the other side of the objective is projected to determine the power density (power per unit area), which is is a more relevant parameter. There is a nice Nature Protocols paper from 2008 that talks about these kinds of measurements, and there is mention about choice of power meter I think:
>>
>> Grunwald, D., et al., Calibrating excitation light fluxes for quantitative light microscopy in cell biology. Nature Protocols, 2008. 3(11): p. 1809-1814.
>>
>> Cheers,
>>
>> John Oreopoulos
>> Staff Scientist
>> Spectral Applied Research
>> Richmond Hill, Ontario
>> Canada
>> www.spectral.ca
>>
>>
>> On 2013-03-12, at 11:17 AM, Martin Seem wrote:
>>
>>> *****
>>> To join, leave or search the confocal microscopy listserv, go to:
>>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>>> *****
>>>
>>> A couple of questions for the list:
>>>
>>> 1, We are currently in the process of buying a new laser power meter that will
>>> primarily be used to check the general stability and power output of the laser
>>> lines of our CLSMs. Have anybody recently bought a power meter after
>>> considering some of currently offered products (like the Coherent LabMax
>>> TOP, Newport 1918-R, GigaHertz PT-9610 and Ophir Vega). Which one did
>>> you choose and why?
>>>
>>> 2, Are there any commercially available laser meter sensors that will allow us
>>> to measure the actual laser light output from a high NA (NA>1) water or oil
>>> immersion objective?
>>>
>>> Martin

[Sylvie Le Guyader]

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

Hi Martin

Last year we bought a Thorlabs meter PM100A and the S130C sensor. We are happy with it.
It was recommended by a Nikon tech, had a reasonable price and data from lasers can be recorded to check over night stability.

Last year we tried the XCite meter with the nice slide-size probe. We can measure power coming from the XCite lamp or from lasers. However we were disappointed to see that we could only record data coming from the XCite lamp. Recording data coming from lasers requires you to press a button at each data point which is silly. Hopefully this has been improved since last year. James can maybe let us know if this is now possible.

Med vänlig hälsning / Best regards
 
Sylvie
 
@@@@@@@@@@@@@@@@@@@@@@@@
Sylvie Le Guyader
Live Cell Imaging Unit
Dept of Biosciences and Nutrition
Karolinska Institutet
Hälsovägen 7
14157 Huddinge
Sweden
office: [phone]
LCI room: [phone]
mobile: [phone]

> -----Original Message-----
> From: Confocal Microscopy List
> [mailto:[hidden email]] On Behalf Of Martin Seem
> Sent: 12 March 2013 16:18
> To: [hidden email]
> Subject: Laser power meter and sensor
>
> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> A couple of questions for the list:
>
> 1, We are currently in the process of buying a new laser power meter that will
> primarily be used to check the general stability and power output of the laser lines
> of our CLSMs. Have anybody recently bought a power meter after considering
> some of currently offered products (like the Coherent LabMax TOP, Newport 1918-
> R, GigaHertz PT-9610 and Ophir Vega). Which one did you choose and why?
>
> 2, Are there any commercially available laser meter sensors that will allow us to
> measure the actual laser light output from a high NA (NA>1) water or oil immersion
> objective?
>
> Martin

[Martin Seem]

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

I would like to thank everybody that has contributed to this tread. I
have read your replies and I appreciate the feedback.

I posted my questions after reading an old listserver thread called "How
to measure objective transmission curves?" (1) from 2007 hoping that a
commercial solution to the challenge of measuring laser power output
from high NA immersion objectives would have been developed and brought
to market since then. I guess it might be possible to make such a
product by combining a small (hyper)hemispherical lens, an integrating
sphere (optional - depending on the acceptance angle of the detector)
and a detector/sensor. Basically a solution similar to the latter part
of the setups described by either (2) or (3). Ideally these parts would
be housed in an enclosure small enough to fit onto the stage of a modern
CLSM. On the basis of the feedback from this thread and after checking
with companies like Coherent and Newport it seems such a product does
not exist. If this is indeed the case its a shame since being able to
accurately measure the amount of excitation light leaving the objective
would have been quite valuable especially when doing any form of live
cell imaging.

In lack of such a product it seems like the method described by Grunwald
et al. (2008) is the next best alternative as long as building a custom
solution is not an option (thanks to John for the reference). I guess a
precise estimate of laser power output could be calculated by
multiplying the data acquired using Grunwalds protocol with the
wavelength specific transmission of the lens (measured using a two
objective setup as suggested by Richard) although this would not be a
particularly simple way of getting the data.

(1)
http://lists.umn.edu/cgi-bin/wa?A2=ind0709&L=CONFOCALMICROSCOPY&D=0&P=3463
(2) Matsuo, S. & Misawa, H. (2002). Direct measurement of laser power
through a high numerical aperture oil immersion objective lens using a
solid immersion lens. Rev. Sci. Instrum. 73(5), page 2011-2015.
(3) Keller, H.E. (2006). Objective lenses for confocal microscopy.
Handbook of Biological Confocal Microscopy, Pawley, J. (ed), Springer
Science+Business Media, New York, page 159.

Martin




On 12.03.2013 19:50, John Oreopoulos wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
>> I wasn't suggesting to use immersion oil on the power meter sensor, and I don't know how those things are engineered
> Yeah, my comment about the absence of immersion medium was actually in reference to Johannes email that came a bit after yours where he said it could be done without immersion medium.
>
>> … although I'm guessing a coevrslip-like protective window in front of the sensor could take care of that problem.
> But in that case, now you've got a glass-air interface between the coverslip and the sensor. You'll get total internal reflection again. You might lose even more power doing it that way because of multiple reflection interfaces... Unless the coverslip is bonded directly to the sensor material...
>
>> However, measuring the power at the nosepiece seems more complicated to me, and then I would have no way to know which fraction of that power actually enters the objective…. For instance, we have two objectives from the same vendor with the same specs (63/1.4 Plan Apo) which have back apertures of different sizes (and one therefore delivers more light to the focal plane, all other thing being equal).
> I think Grunwald's method addresses this point by inserting an adjustable aperture at the nosepiece which can be set to match the back-aperture diameter of the objectives in question.
>
>> On the other hand, if the power meter sensor is fairly large and is held pretty close to the front element of the lens, I suspect the error due to rays that miss the sensor (i.e rays at close to 180 degrees, would be pretty small… certainly smaller in my opinion to the error in estimating how much light coming out of the nosepiece actually enters the objective.
> The critical angle for glass-air is somewhere around 45 degrees I think. A high NA oil-immersion objective can easily direct light rays towards a point up to 75 degrees with the oil and the coverslip. I think you'd be a fair chunk of the light in that case (anything between 45 and 75 degrees).
>
> It's a good question though about which method is more accurate. If I had the time, I'd do a comparison between the method described by Grunwald et al and this method of protecting a large sensor power meter with a coverslip. Anyone else out there care to try that? Could make for a nice, short technical paper.
>
> Cheers,
>
> John Oreopoulos
>
>
>
>
> On 2013-03-12, at 2:18 PM, Vazquez Lopez, Julio wrote:
>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>> *****
>>
>> I wasn't suggesting to use immersion oil on the power meter sensor, and I don't know how those things are engineered… although I'm guessing a coevrslip-like protective window in front of the sensor could take care of that problem.
>>
>> However, measuring the power at the nosepiece seems more complicated to me, and then I would have no way to know which fraction of that power actually enters the objective…. For instance, we have two objectives from the same vendor with the same specs (63/1.4 Plan Apo) which have back apertures of different sizes (and one therefore delivers more light to the focal plane, all other thing being equal).
>>
>> On the other hand, if the power meter sensor is fairly large and is held pretty close to the front element of the lens, I suspect the error due to rays that miss the sensor (i.e rays at close to 180 degrees, would be pretty small… certainly smaller in my opinion to the error in estimating how much light coming out of the nosepiece actually enters the objective.
>>
>> Julio.
>>
>>
>>
>> ----- Original Message -----
>> From: "John Oreopoulos" <[hidden email]>
>> To: [hidden email]
>> Sent: Tuesday, March 12, 2013 10:04:08 AM
>> Subject: Re: Laser power meter and sensor
>>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>> *****
>>
>> Julio, on the specifications tab of the weblink you sent, it says regarding objective compatibility:
>>
>> 4X-63X; air coupled, with FOV diameters less than 10mm
>>
>> Just to re-iterate, I don't think you can use an immersion objective with a power meter like this (someone from Lumen Dynamics can confirm this). Not only would it require you to place the optical sensor in contact with the immersion fluid of the objective (which might damage it), but even if you could do that, it still wouldn't work because these devices have a low acceptance angle for light, that is to say, these devices won't capture/register the light that approaches the sensor at very oblique angles which are typically present when using high NA immersion objectives.
>>
>> The absence of the immersion medium is also not an option because then many of the oblique rays will be lost at the front lens due to total internal reflection at the glass-air interface.
>>
>> John Oreopoulos
>>
>>
>> On 2013-03-12, at 12:38 PM, Vazquez Lopez, Julio wrote:
>>
>>> *****
>>> To join, leave or search the confocal microscopy listserv, go to:
>>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>>> *****
>>>
>>> You can check this:
>>>
>>> http://www.ldgi-xcite.com/products-xr2100-xp750.php
>>>
>>> We use a similar meter from Coherent, but i'm not in the lab now and can't tell you the model #.  We routinely use power at the focal plane with up to 20x objectives. Not sure how accurate it would be with high NA… depends on how close you can get to the objective…
>>>
>>> Julio Vazquez.
>>>
>>>
>>> ----- Original Message -----
>>> From: "John Oreopoulos" <[hidden email]>
>>> To: [hidden email]
>>> Sent: Tuesday, March 12, 2013 9:09:35 AM
>>> Subject: Re: Laser power meter and sensor
>>>
>>> *****
>>> To join, leave or search the confocal microscopy listserv, go to:
>>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>>> *****
>>>
>>> Hi Martin, it regards to question 2, I don't think such a power meter exists (although if someone else knows otherwise, I'd love to know as well). You're better off measuring the power at the back of the objective (ie: unscrew the objective and measure the power at the empty nosepiece), and then use the wavelength transmission curve of the objective (usually available from the manufacturer) to calculate the percentage of light that gets through to the front end of the objective - some error is introduced here as there is some variability in the transmission for each identical objective, but at least you get a good estimate of the actual power on the other side of the objective.
>>>
>>> You might also consider over what area that power that gets to the other side of the objective is projected to determine the power density (power per unit area), which is is a more relevant parameter. There is a nice Nature Protocols paper from 2008 that talks about these kinds of measurements, and there is mention about choice of power meter I think:
>>>
>>> Grunwald, D., et al., Calibrating excitation light fluxes for quantitative light microscopy in cell biology. Nature Protocols, 2008. 3(11): p. 1809-1814.
>>>
>>> Cheers,
>>>
>>> John Oreopoulos
>>> Staff Scientist
>>> Spectral Applied Research
>>> Richmond Hill, Ontario
>>> Canada
>>> www.spectral.ca
>>>
>>>
>>> On 2013-03-12, at 11:17 AM, Martin Seem wrote:
>>>
>>>> *****
>>>> To join, leave or search the confocal microscopy listserv, go to:
>>>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>>>> *****
>>>>
>>>> A couple of questions for the list:
>>>>
>>>> 1, We are currently in the process of buying a new laser power meter that will
>>>> primarily be used to check the general stability and power output of the laser
>>>> lines of our CLSMs. Have anybody recently bought a power meter after
>>>> considering some of currently offered products (like the Coherent LabMax
>>>> TOP, Newport 1918-R, GigaHertz PT-9610 and Ophir Vega). Which one did
>>>> you choose and why?
>>>>
>>>> 2, Are there any commercially available laser meter sensors that will allow us
>>>> to measure the actual laser light output from a high NA (NA>1) water or oil
>>>> immersion objective?
>>>>
>>>> Martin