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How are green laser diodes changing biomedical diagnostics?

steve001

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Alaskan

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Aha, those side lobe outputs are well known for these diodes

The typical beam output of single-mode laser diodes is highly divergent and asymmetrical, but the emitter size is usually smaller than 1 µm, making it relatively easy to collimate the beam with very small optics and couple into a single-mode fiber. However, an issue that can occur in some laser diodes is the undesired appearance of a ghost side lobe. The side lobe typically accounts for 1–2% of the total light. While this ghost is very faint, it interacts with the optical system and can easily distort measurement, making optical design much more challenging. The ghost side lobe only appears with some lasers, and the strength of the side lobe varies from laser diode to laser diode.

Osram has investigated the causes of these unwanted side lobes and developed a set of manufacturing protocols to correct the issue. Osram’s solution, Brilliant Beam Technology, efficiently suppresses the side lobes at their origin and ensures a dependable far-field beam quality that resembles a perfect Gaussian single mode (see Fig. 3). This technology creates much more reliable laser diode characteristics, even in the large populations. The ultimate benefit is higher yields in production.
 

steve001

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Aha, those side lobe outputs are well known for these diodes
But it can be dealt with.

P.S. You and me appreciate low divergence. Take a look at this laser sight.

https://www.ncstar.com/optics-acc/lasers/blue-laser/vaprlsmblv2-lsrbluecmpstrbpicgen-2
SPECIFICATIONS:
BLUE LASER:
 Wavelength: 450 nm
 Maximum Output Power; 5mW
 Operating Voltage: 3V DC
 Operation Current:35-50 mA
 Line Width:10 nm

Beam Divergence: 0.01 mrad

 Beam diameter: <20mm @ 20 yards
 Battery type: CR 1/3N (3V Lithium Battery)
 Requires two each Batteries
 Material: Aluminum Body
 Material: Plastic Battery Door
 Finish: Black Anodized
 Length: 2.0”
 Width: 1.1”
 Overall Height: 1.1”
 Weight: 1.6 oz. (without batteries)
 Weight: 1.8 oz. (with batteries)
 
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Alaskan

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I don't believe their divergence figure with that small of an output aperture.
 

paul1598419

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I remember studying flow cytometry in immunology, a course I took back in the 1990s. There are all sorts of uses for lasers that most people never hear about.
 

steve001

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I don't believe their divergence figure with that small of an output aperture.
I don't see anything about aperture.

I remember studying flow cytometry in immunology, a course I took back in the 1990s. There are all sorts of uses for lasers that most people never hear about.
It's remarkable what useful things can done using lasers besides burning stuff.
 
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Alaskan

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It's the size of the module, looking at that hole it must be very small, I just don't see how they could get that low of a divergence, how big do you think that aperture is?
 

jnrpop

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I guess we'll all be seeing alot of DPSS units for sale on e..bay in the near future. Osrams really creating beautiful products, to guarantee thier PLT5-488 diode has +-2nm is awesome. :D
 

steve001

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It's the size of the module, looking at that hole it must be very small, I just don't see how they could get that low of a divergence, how big do you think that aperture is?
It's difficult to say how wide the aperture is. Even looking at their vids doesn't help. What would be helpful is a beam width measurement at a greater distance, say 100 feet. If the specification is accurate I wonder how it is accomplished in such a short distance. I took a look a the green version it has a divergence of less than 1mrad with a beam diameter of 1mm. After a little thought it can be done when the laser beam waist is wider initially.
 
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ZRaffleticket

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You know, after seeing that osram acknowledges the phantom square and makes a point to eliminate it, I think we can actually see some of that in action if we look at the raw diode output:

PLT5-488:


vs Sharp 495


Notice on the right side how the osram diode seems to taper off, where it doesn't on the sharp diode.

Looking at where that corresponds to in the diode, that is on the top of the diode (right side in picture, where the bottom is the base/heatsink the die rests on)


With the osram diodes, there is no phantom square to speak of. but with the sharp diodes, the phantom square appears on the top section of the diode (where osram diodes taper off, but the sharp diodes do not):


When I saw this with the PLT5-488 I have, I just thought it was a manufacturing defect. Now I'm thinking it's a very much needed feature... can anyone else give more input?

Very cool article to share! I'm glad we finally see these awesome wavelengths at affordable prices
 

steve001

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You know, after seeing that osram acknowledges the phantom square and makes a point to eliminate it, I think we can actually see some of that in action if we look at the raw diode output:

PLT5-488:


vs Sharp 495


Notice on the right side how the osram diode seems to taper off, where it doesn't on the sharp diode.

Looking at where that corresponds to in the diode, that is on the top of the diode (right side in picture, where the bottom is the base/heatsink the die rests on)


With the osram diodes, there is no phantom square to speak of. but with the sharp diodes, the phantom square appears on the top section of the diode (where osram diodes taper off, but the sharp diodes do not):


When I saw this with the PLT5-488 I have, I just thought it was a manufacturing defect. Now I'm thinking it's a very much needed feature... can anyone else give more input?

Very cool article to share! I'm glad we finally see these awesome wavelengths at affordable prices
In my limited experience with a sanwu 405nm laser the raw output has one of those arcs. With a lens in place as the output is collimated that arc becomes a partial square.
 

paul1598419

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That is an interesting theory, but the rectangular artifact appears to a reflection of the die. If that is the case, the differences in the diodes are just that....different.
 

Benm

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I don't believe their divergence figure with that small of an output aperture.
I have my doubts as well - it states a beam diamter of <20 mm at 20 meters distance, i'll just assume that the beam straight out of the laser has been expanded to 20 mm diameter.

With optics you trade change beam diameter for diameter, at any ratio in theory.

So if this laser had been collimated to a fairly narror 2 mm beam diameter instead, it should have a divergence of just 0.1 mrad. That would be -extremely- good, not really achievable with a direct diode laser unless the diode was something really special. Even most dpps systems don't come even close to such spec, certainly not those in pointers etc.
 

steve001

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I have my doubts as well - it states a beam diamter of <20 mm at 20 meters distance, i'll just assume that the beam straight out of the laser has been expanded to 20 mm diameter.

With optics you trade change beam diameter for diameter, at any ratio in theory.

So if this laser had been collimated to a fairly narror 2 mm beam diameter instead, it should have a divergence of just 0.1 mrad. That would be -extremely- good, not really achievable with a direct diode laser unless the diode was something really special. Even most dpps systems don't come even close to such spec, certainly not those in pointers etc.
Their one particular green laser has good divergence <1 mrad with a beam diameter of 1mm according to the specification. It's possible the blue spec is correct - maybe.
 

Benm

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1 mrad at 1mm diameter would still scale to 'only' 0.05 mrad at 20mm diameter, not to 0.01. It's impressive none the less.
 




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