Laser noise

[GregS]

I was trying to attempt to measure noise on a 6 watt laser. The main problem
is trying to focus on something without it melting or catching fire.
I was trying to look at the reflective light withg a photodiode.
I guess there migh be some fancy expensive device ??

greg

 

On Thu, 04 Mar 2010 17:15:05 GMT, zekfrivo@zekfrivolous.com
(GregS)wrote:

I was trying to attempt to measure noise on a 6 watt laser. The main problem
is trying to focus on something without it melting or catching fire.
I was trying to look at the reflective light withg a photodiode.
I guess there migh be some fancy expensive device ??

greg

Indium Gallium Arsenide power wavehead photodetector.

 

[William Sommerwerck]

What about using a lens to spread the light?

 

On Thu, 4 Mar 2010 10:09:27 -0800, "William Sommerwerck"
<grizzledgeezer@comcast.net>wrote:

What about using a lens to spread the light?

Wouldn't that effect or distort the noise or influence the reading
otherwise?

 

[William Sommerwerck]

What about using a lens to spread the light?

Wouldn't that affect or distort the noise or influence
the reading otherwise?

Well, at the least it would reduce the absolute value of noise read. But if
the light were spread evenly, and you knew the area ratio of spread to
direct light...

 

On Thu, 4 Mar 2010 10:34:36 -0800, "William Sommerwerck"
<grizzledgeezer@comcast.net>wrote:

What about using a lens to spread the light?

Wouldn't that affect or distort the noise or influence
the reading otherwise?

Well, at the least it would reduce the absolute value of noise read. But if
the light were spread evenly, and you knew the area ratio of spread to
direct light...

True if you had the ratio just do the math.

 

[GregS]

In article <hmouge$19m$1@news.eternal-september.org>, "William Sommerwerck" <grizzledgeezer@comcast.net> wrote:

What about using a lens to spread the light?

Wouldn't that affect or distort the noise or influence
the reading otherwise?

Well, at the least it would reduce the absolute value of noise read. But if
the light were spread evenly, and you knew the area ratio of spread to
direct light...

Spreading would be fine, as long as it does not spread to my eyes.
But thats a good idea.

greg

 

[AZ Nomad]

On Thu, 04 Mar 2010 17:15:05 GMT, GregS <zekfrivo@zekfrivolous.com> wrote:

I was trying to attempt to measure noise on a 6 watt laser. The main problem
is trying to focus on something without it melting or catching fire.
I was trying to look at the reflective light withg a photodiode.
I guess there migh be some fancy expensive device ??

Like a filter?

 

[Phil Hobbs]

On 3/4/2010 12:15 PM, GregS wrote:

I was trying to attempt to measure noise on a 6 watt laser. The main problem
is trying to focus on something without it melting or catching fire.
I was trying to look at the reflective light withg a photodiode.
I guess there migh be some fancy expensive device ??

greg

Three front-surface reflections from window glass, plus an ordinary
photodiode. Make sure the multiple reflections miss each other.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

 

[William Sommerwerck]

Three front-surface reflections from window glass, plus an ordinary
photodiode. Make sure the multiple reflections miss each other.

So you'd have 4% of 4% of 4%, or about .000064 of the original energy,
right?

 

[tm]

"GregS" <zekfrivo@zekfrivolous.com> wrote in message
news:hmopjo$4m6$1@usenet01.srv.cis.pitt.edu...

I was trying to attempt to measure noise on a 6 watt laser. The main
problem
is trying to focus on something without it melting or catching fire.
I was trying to look at the reflective light withg a photodiode.
I guess there migh be some fancy expensive device ??

greg

Use a clear optical glass beam splitter. Pick the incident angle to
get as much or less as you want. Terminate the beam into a beam stop
(brick?).

T

 

[Samuel M. Goldwasser]

zekfrivo@zekfrivolous.com (GregS) writes:

I was trying to attempt to measure noise on a 6 watt laser. The main problem
is trying to focus on something without it melting or catching fire.
I was trying to look at the reflective light with a photodiode.
I guess there migh be some fancy expensive device ??

All sorts of ways of reducing the power density including lenses to spread it
(as someone else mentioned), or a simple beam sampler using a glass plate to
pick up 8 or 10 percent. A couple times and you get down to reasonable power
levels. Or get a proper beamsplitter that can be obtained to reflect
a very low percentage of the beam power. An optical filter or even a mirror
that reflects most of the beam and transmits a small percentage can also be
used, but probably only after the lens to reduce the power density so as not
to damage it.

Then any photodiode will be fine.

Those expensive devices have some means of reducing the power to acceptable
levels for their sensors.

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[Samuel M. Goldwasser]

Meat Plow writes:

What about using a lens to spread the light?

Wouldn't that effect or distort the noise or influence the reading
otherwise?

Not as long as the noise relative to the total power into the sensor
is what's measured.

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[Robert Macy]

On Mar 4, 4:01 pm, s...@repairfaq.org (Samuel M. Goldwasser) wrote:

Meat Plow writes:
What about using a lens to spread the light?
Wouldn't that effect or distort the noise or influence the reading
otherwise?

Not as long as the noise relative to the total power into the sensor
is what's measured.

--
    sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
 Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
        | Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line.  Or, you can contact me via the Feedback Form in the FAQs..

Pre-apologize for the naive question:
Are you measuring amplitude noise and/or spectral noise?
Are these valid questions?

 

[Phil Hobbs]

On 3/4/2010 5:49 PM, William Sommerwerck wrote:

Three front-surface reflections from window glass, plus an ordinary
photodiode. Make sure the multiple reflections miss each other.

So you'd have 4% of 4% of 4%, or about .000064 of the original energy,
right?

Depends on the angle, but it's that order of magnitude. Figuring 5% per
bounce, that 6 W comes down to about 750 uW. Keeping the reflections
from overlapping is really key--interference between the different beams
will make the ratio go all over the place.

Ordinary hardware store black paint, e.g. ultra-flat black Krylon, is a
really really good index match to fused quartz, so if you have a
quarter-inch quartz windows lying around, you can come in at a fairly
oblique angle, let it bounce around inside a few times, and pick the
reflection you want. If the angle of incidence is more than, say, 20
degrees, you have to worry about the polarization dependence of the
reflection coefficient.

Laser noise is commonly space- and polarization-dependent--it's a
surprisingly deep subject.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

 

[Phil Hobbs]

On 3/4/2010 7:01 PM, Samuel M. Goldwasser wrote:

Meat Plow writes:

What about using a lens to spread the light?

Wouldn't that effect or distort the noise or influence the reading
otherwise?

Not as long as the noise relative to the total power into the sensor
is what's measured.

That's true only if the beam isn't vignetted--i.e. if you use a lens to
spread the 6W out over a solar cell that can handle the power. Laser
noise (especially in gas and diode lasers) often has a pronounced
spatial variation. For instance, when there are multiple modes, each
mode in itself may be much noisier than the total beam.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

 

On 04 Mar 2010 19:01:38 -0500, sam@repairfaq.org (Samuel M.
Goldwasser)wrote:

Meat Plow writes:

What about using a lens to spread the light?

Wouldn't that effect or distort the noise or influence the reading
otherwise?

Not as long as the noise relative to the total power into the sensor
is what's measured.

I like spitting the beam with a diffraction grating or even with a
pair of these newer 3D glasses.

 

[GregS]

In article <f85b3ee2-2adb-43e9-a16f-825259a9ed24@w27g2000pre.googlegroups.com>, Robert Macy <macy@california.com> wrote:

On Mar 4, 4:01=A0pm, s...@repairfaq.org (Samuel M. Goldwasser) wrote:
Meat Plow writes:
What about using a lens to spread the light?
Wouldn't that effect or distort the noise or influence the reading
otherwise?

Not as long as the noise relative to the total power into the sensor
is what's measured.

--
=A0 =A0 sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
=A0Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
=A0 =A0 =A0 =A0 | Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.h=
tml

Important: Anything sent to the email address in the message header above=
is
ignored unless my full name AND either lasers or electronics is included =
in the
subject line. =A0Or, you can contact me via the Feedback Form in the FAQs=
..

Pre-apologize for the naive question:
Are you measuring amplitude noise and/or spectral noise?
Are these valid questions?

I'm mostly concerned with power supply noise or whatever is predominant.

greg

 

[Samuel M. Goldwasser]

zekfrivo@zekfrivolous.com (GregS) writes:

In article <f85b3ee2-2adb-43e9-a16f-825259a9ed24@w27g2000pre.googlegroups.com>, Robert Macy <macy@california.com> wrote:
On Mar 4, 4:01=A0pm, s...@repairfaq.org (Samuel M. Goldwasser) wrote:
Meat Plow writes:
What about using a lens to spread the light?
Wouldn't that effect or distort the noise or influence the reading
otherwise?

Not as long as the noise relative to the total power into the sensor
is what's measured.

--
=A0 =A0 sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/

Pre-apologize for the naive question:
Are you measuring amplitude noise and/or spectral noise?
Are these valid questions?

I'm mostly concerned with power supply noise or whatever is predominant.

What type of laser are you using (sorry if I forgot!)?

If it's a diode laser, looking at an electrical signal from the power supply
that corresponds to the laser diode current may be nearly as good as looking
at the laser's output and doesn't require a sensor.

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[GregS]

In article <ubpeyfj15.fsf@repairfaq.org>, sam@repairfaq.org (Samuel M. Goldwasser) wrote:

zekfrivo@zekfrivolous.com (GregS) writes:

In article
f85b3ee2-2adb-43e9-a16f-825259a9ed24@w27g2000pre.googlegroups.com>, Robert
Macy <macy@california.com> wrote:
On Mar 4, 4:01=A0pm, s...@repairfaq.org (Samuel M. Goldwasser) wrote:
Meat Plow writes:
What about using a lens to spread the light?
Wouldn't that effect or distort the noise or influence the reading
otherwise?

Not as long as the noise relative to the total power into the sensor
is what's measured.

--
=A0 =A0 sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/

Pre-apologize for the naive question:
Are you measuring amplitude noise and/or spectral noise?
Are these valid questions?

I'm mostly concerned with power supply noise or whatever is predominant.

What type of laser are you using (sorry if I forgot!)?

If it's a diode laser, looking at an electrical signal from the power supply
that corresponds to the laser diode current may be nearly as good as looking
at the laser's output and doesn't require a sensor.

Right, but getting to the right point is somewhat of a risk. I don't want to send anymore lasers back to China.

Greg