Laser pointer discussion. Read/write reviews of laser pointers and laser pointer companies. Learn about all types of laser pointers and lasers





Welcome to Laser Pointer Forums! If you are looking for a laser pointer or want to compare different laser pointer companies, you may want to check out the LPF Laser Pointer Company Database. The link will open in a new window for your convenience.








Green Laser Pointers by Category Blue Laser Pointers by Category Red Laser Pointers by Category
Yellow Laser Pointers by Category Violet Laser Pointers by Category Orange Laser Pointers by Category
Top Laser Pointers by Power - 1 Watt+ Top Laser Pointers by Power - 500mW+ Top Laser Pointers by Power - 250mW+
Laser Pointer Database High Power Laser Pointers Laser Pointer Diodes
Laser Technology Laser Pointer Parts Lasers by Wavelength
Top 10 Laser Pointer Companies Laser Pointer Company Database Visible Beam Laser Pointers


One laser store meets all your needs

























Go Back   Laser Pointer Forums - Discuss Laser Pointers > Lasers > Science & Lasers



LPF List of Laser Pointer Companies (link opens new window)



Reply
 
LinkBack Thread Tools Display Modes
Old 04-20-2012, 01:58 AM #1
lasergal's Avatar
Class 1M Laser
 
Join Date: Apr 2012
Location: Pacific Northwest, USA
Posts: 130
Rep Power: 24
lasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant future
lasergal lasergal is offline
Class 1M Laser
lasergal's Avatar
 
Join Date: Apr 2012
Location: Pacific Northwest, USA
Posts: 130
Rep Power: 24
lasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant future
Question Why are diode lasers different?

Sorry if this has been discussed elsewhere, but I searched and Googled and still can't find a satisfactory answer, and this question has nagged me for years:

If one of the chief characteristics of laser light is its coherence, why then are the beams from diode lasers any less coherent than from other types of lasers? I've read that diode coherence is inferior to, say, a HeNe so many times I stopped counting. But never have I found a really good explanation for this.

Diode lasers are still real lasers, right? So why do they need special lenses to focus the beam into a tight line, and other lasers don't?

Could someone explain it to me so even my "typical female" mind can understand? I'd appreciate it!

And I do apologize if I'm


lasergal is offline   Reply With Quote







LPF List of Laser Pointer Companies (link opens new window)







Old 04-20-2012, 02:05 AM #2
Sigurthr's Avatar
Class 3B Laser
 
Join Date: Dec 2011
Location: Michigan's U.P.
Posts: 4,382
Rep Power: 873
Sigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond repute
Sigurthr Sigurthr is offline
Class 3B Laser
Sigurthr's Avatar
 
Join Date: Dec 2011
Location: Michigan's U.P.
Posts: 4,382
Rep Power: 873
Sigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond repute
Default Re: Why are diode lasers different?

In a gas laser the bore shape yields the round spot and only light which is directly parallel to the bore gets amplified and emitted.

In a diode laser the active emitter area is super tiny, and can be considered a point source for many things, but it is not really a point source when you get down small enough. This is analogous to an isotropic antenna (it doesn't exist in the real world, nothing is infinitely small). Also, IIRC the photons don't pass through the gain medium as many times in diode lasers, and with each pass through a gain medium (and thus each reflection by the mirrors) the non parallel photons get weeded out. So, in a diode you have a definite emitter area where photons are emitted not just parallel to the axis of the mirrors but also in a cone, and there is less filtration of non-parallel photons.

It is because the diode's photons are emitted in a cone shape that we need a lens to focus it in to a beam.
__________________
Amateur Multispectral Photographer - [X-Ray, UV, Vis, IR]
Amateur Electrical Engineer
Autodidact
Tesla Coil Expert
Sigurthr is offline   Reply With Quote
Old 04-20-2012, 02:09 AM #3
lasergal's Avatar
Class 1M Laser
 
Join Date: Apr 2012
Location: Pacific Northwest, USA
Posts: 130
Rep Power: 24
lasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant future
lasergal lasergal is offline
Class 1M Laser
lasergal's Avatar
 
Join Date: Apr 2012
Location: Pacific Northwest, USA
Posts: 130
Rep Power: 24
lasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant future
Default Re: Why are diode lasers different?

Ah, okay. So it has to do with the shape of the diode then?
lasergal is offline   Reply With Quote
Old 04-20-2012, 02:50 AM #4
Sigurthr's Avatar
Class 3B Laser
 
Join Date: Dec 2011
Location: Michigan's U.P.
Posts: 4,382
Rep Power: 873
Sigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond repute
Sigurthr Sigurthr is offline
Class 3B Laser
Sigurthr's Avatar
 
Join Date: Dec 2011
Location: Michigan's U.P.
Posts: 4,382
Rep Power: 873
Sigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond reputeSigurthr has a reputation beyond repute
Default Re: Why are diode lasers different?

Not of the diode but of the part of the diode inside that actually produces the light. More so size than shape, to be accurate.
__________________
Amateur Multispectral Photographer - [X-Ray, UV, Vis, IR]
Amateur Electrical Engineer
Autodidact
Tesla Coil Expert
Sigurthr is offline   Reply With Quote
Old 04-20-2012, 04:05 AM #5
Hiemal's Avatar
Class 3R Laser
 
Join Date: Dec 2011
Location: Houston, TX
Posts: 1,449
Rep Power: 311
Hiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond repute
Hiemal Hiemal is offline
Class 3R Laser
Hiemal's Avatar
 
Join Date: Dec 2011
Location: Houston, TX
Posts: 1,449
Rep Power: 311
Hiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond reputeHiemal has a reputation beyond repute
Default Re: Why are diode lasers different?

Basically, there's a lot more area "emitting" laser light in a HeNe tube, therefore it doesn't need optics to produce a dot...however, as you can probably tell, tubes aren't exactly high power.

Because of the size of a laser diode the photons tend to scatter out in a oval/circular shape and thus require a lens to collimate them together nicely.
__________________
formerly Le Quack


Drivers and Stuff

Superboost Driver (5.5+ amp capability) End all for Boosting!

MicroSized Boost Driver

Low Dropout Linear Driver


Any electronics related questions?

Send me a PM and I'll try my best to answer!
Hiemal is offline   Reply With Quote
Old 04-20-2012, 04:35 AM #6
lasergal's Avatar
Class 1M Laser
 
Join Date: Apr 2012
Location: Pacific Northwest, USA
Posts: 130
Rep Power: 24
lasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant future
lasergal lasergal is offline
Class 1M Laser
lasergal's Avatar
 
Join Date: Apr 2012
Location: Pacific Northwest, USA
Posts: 130
Rep Power: 24
lasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant future
Default Re: Why are diode lasers different?

Thanks, that helps me understand it.
lasergal is offline   Reply With Quote
Old 04-20-2012, 10:39 PM #7
MadEye's Avatar
Class 1M Laser
 
Join Date: Aug 2011
Posts: 129
Rep Power: 27
MadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond repute
MadEye MadEye is offline
Class 1M Laser
MadEye's Avatar
 
Join Date: Aug 2011
Posts: 129
Rep Power: 27
MadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond reputeMadEye has a reputation beyond repute
Default Re: Why are diode lasers different?

Reading your question I think you dont really know what coherence really means. Coherence means the waves are of the same wavelength and are in phase with each other. So an output directly of a laser diode is exactly as coherent as the beam after it got focused to infinity.

But your main question was already answered
__________________
405nm: 100mW
405nm: 400mW C6 S06J

445nm: 1W C6
445nm: 1W DIY Labby LINK
532nm: 30mW
532nm: 400mW

655nm: 5mW DIY Pen
660nm: 250mW

3.2W LaserBee II
MadEye is offline   Reply With Quote
Old 04-21-2012, 12:09 AM #8
Benm's Avatar
Class 4 Laser
 
Join Date: Aug 2007
Location: Netherlands
Posts: 7,439
Rep Power: 18210
Benm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond repute
Benm Benm is online now
Class 4 Laser
Benm's Avatar
 
Join Date: Aug 2007
Location: Netherlands
Posts: 7,439
Rep Power: 18210
Benm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond repute
Default Re: Why are diode lasers different?

It doesnt depend on how you focus the light using lenses, but the coherence length of light from a laser diode is inferior to that of, say, a HeNe for the reasons descibed above.
Benm is online now   Reply With Quote
Old 04-21-2012, 06:16 AM #9
Banned
 
Join Date: Apr 2012
Location: Behind the Midas.
Posts: 57
Rep Power: 0
Oceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to behold
Oceansoul Oceansoul is offline
Banned
 
Join Date: Apr 2012
Location: Behind the Midas.
Posts: 57
Rep Power: 0
Oceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to behold
Default Re: Why are diode lasers different?

Firstly, divergence at aperture =/= coherence length.

Both the coherence length of the beam and the divergence at aperture are proportional to the length of the gain medium

A longer gain medium will produce beams with both better divergence (we're talking <0.9mRad at 1-2mm beam diameter here from a large-frame ArIon), as well as beams with a longer coherence length.

The length of the gain medium on a diode laser is measured in micrometers. It's tiny. The beam diameter upon leaving the gain medium is also tiny, and because beam diameter is proportional to divergence, the divergence is huge.

The collimating lens just keeps the expansion in check.

That's how beam expanders work, by the way. They trade off beam diameter for divergence.

Fact: y'know your average DPSS module? It's no better. The beam that leaves the front-side of the KTP is around the same diameter as that leaving a diode laser's gain medium (often smaller). It gets blown up a bit more by an expanding lens and then gets collimated again. That's why DPSS laser modules have a focusing lens as well.

The fact that taking the collimating lens off a diode laser or a DPSS laser module turns it into a flashlight doesn't make it any less of a 'real' laser. It's still coherent light, it's just that you're dealing with a tiny beam diameter and massive resultant divergence.

Both the HeNe and the diode laser are coherent; the distinction comes from the fact that they're coherent to different degrees.

Secondly, the books are talking about temporal coherence, not spatial coherence.

Put in really simple terms: that's the degree to which the beam is coherent if you travel down the beam longitudinally.

Diode lasers don't exactly have spectacular spatial coherence either; they're incredibly 'noisy' (the output is not always stable). This comes from the fact that they're driven by a power supply that may experience fluctuations in current (which leads to a change in output power).

Last edited by Oceansoul; 04-21-2012 at 06:30 AM.
Oceansoul is offline   Reply With Quote
Old 04-21-2012, 06:18 AM #10
lasergal's Avatar
Class 1M Laser
 
Join Date: Apr 2012
Location: Pacific Northwest, USA
Posts: 130
Rep Power: 24
lasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant future
lasergal lasergal is offline
Class 1M Laser
lasergal's Avatar
 
Join Date: Apr 2012
Location: Pacific Northwest, USA
Posts: 130
Rep Power: 24
lasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant futurelasergal has a brilliant future
Default Re: Why are diode lasers different?

"Coherence means the waves are of the same wavelength..."

I thought that was what 'monochromatic' means- the same wavelength (color). Not coherence.

Coherence is the "and are in phase with each other" part.
lasergal is offline   Reply With Quote
Old 04-21-2012, 06:30 AM #11
Banned
 
Join Date: Apr 2012
Location: Behind the Midas.
Posts: 57
Rep Power: 0
Oceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to behold
Oceansoul Oceansoul is offline
Banned
 
Join Date: Apr 2012
Location: Behind the Midas.
Posts: 57
Rep Power: 0
Oceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to beholdOceansoul is a splendid one to behold
Default Re: Why are diode lasers different?

Quote:
Originally Posted by lasergal View Post
"Coherence means the waves are of the same wavelength..."

I thought that was what 'monochromatic' means- the same wavelength (color). Not coherence.

Coherence is the "and are in phase with each other" part.
Monochromatic: the waves are the same wavelength.

Coherence: the waves are in phase with each other.

Spatial coherence: (coherence in space) the wavefronts are in phase with each other.

Temporal coherence: (coherence in time) the power and wavelength of the beam remains consistent throughout the length of the beam.

Last edited by Oceansoul; 04-27-2012 at 08:06 AM.
Oceansoul is offline   Reply With Quote
Old 06-05-2012, 06:24 AM #12
Class 1 Laser
 
Join Date: Jun 2012
Posts: 57
Rep Power: 9
Videogamer555 is just really niceVideogamer555 is just really niceVideogamer555 is just really niceVideogamer555 is just really nice
Videogamer555 Videogamer555 is offline
Class 1 Laser
 
Join Date: Jun 2012
Posts: 57
Rep Power: 9
Videogamer555 is just really niceVideogamer555 is just really niceVideogamer555 is just really niceVideogamer555 is just really nice
Default Re: Why are diode lasers different?

Quote:
Originally Posted by Sigurthr View Post
In a gas laser the bore shape yields the round So, in a diode you have a definite emitter area where photons are emitted not just parallel to the axis of the mirrors but also in a cone, and there is less filtration of non-parallel photons.

It is because the diode's photons are emitted in a cone shape that we need a lens to focus it in to a beam.

Still not quite true. In a laser several factors must be present simultaneously.

1: 2 paralel mirrors (doesn't work if not paralell and a lasing medium
2: distance between mirrors must be exactly equal to wavelength of light to amplify (much like "tuning" the length of an antanna to the right RF frequency).


The distance between the center of one mirror and the center of the other mirror is EXACTLY a multiple of the wavelength to amplify. However ANY photons bouncing at even a SLIGHT angle will travel a longer distance between mirrors, and thus will NOT cause laser amplification. So even in a DIODE laser, it should be a PERFECTLY PARALLEL SIDED beam emerging from the device. The fact that it does NOT do so, has baffeled scientists for a long time.
Videogamer555 is offline   Reply With Quote
Old 06-05-2012, 02:25 PM #13
BShanahan14rulz's Avatar
Class 3B Laser
 
Join Date: Dec 2009
Posts: 3,175
Rep Power: 264
BShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond repute
BShanahan14rulz BShanahan14rulz is offline
Class 3B Laser
BShanahan14rulz's Avatar
 
Join Date: Dec 2009
Posts: 3,175
Rep Power: 264
BShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond reputeBShanahan14rulz has a reputation beyond repute
Default Re: Why are diode lasers different?

I think the trend is the longer your cavity, the lower your base divergence.
BShanahan14rulz is offline   Reply With Quote
Old 06-05-2012, 02:35 PM #14
Class 4 Laser
 
Join Date: Nov 2008
Posts: 5,728
Rep Power: 547
ElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond repute
ElektroFreak ElektroFreak is offline
Class 4 Laser
 
Join Date: Nov 2008
Posts: 5,728
Rep Power: 547
ElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond repute
Default Re: Why are diode lasers different?

^yep. A tiny cavity like that which is found in a laser diode will always produce a highly diverging raw beam before correction. The same is true in most of our hobbyist-class DPSS lasers too, due to the fact that the cavity is usually between a few mm (in the case of bonded crystals) and a couple inches (discrete crystals) long. In contrast, most gas lasers have long cavities, between 6 inches and several feet. They produce well collimated beams naturally, without any further lenses or optics.
__________________
Laser Resources (for n00bs and veterans alike!)

Sam's Laser FAQ (The Laser Bible)

http://www.repairfaq.org/sam/laserfaq.htm

RP Photonics Encyclopedia of Laser Physics and Technology

http://www.rp-photonics.com/encyclopedia.html

ULTIMATE DIY PROJECTOR REFERENCE

http://nqlasers.com/scannerreference...itle=Main_Page

SUCCESS is the best revenge.
ElektroFreak is offline   Reply With Quote
Old 06-05-2012, 08:03 PM #15
Class 1 Laser
 
Join Date: Jun 2012
Posts: 57
Rep Power: 9
Videogamer555 is just really niceVideogamer555 is just really niceVideogamer555 is just really niceVideogamer555 is just really nice
Videogamer555 Videogamer555 is offline
Class 1 Laser
 
Join Date: Jun 2012
Posts: 57
Rep Power: 9
Videogamer555 is just really niceVideogamer555 is just really niceVideogamer555 is just really niceVideogamer555 is just really nice
Default Re: Why are diode lasers different?

Why is the beam more divergent in one axis than in the other (and thus forming an elliptical rather than circular beam)?
Videogamer555 is offline   Reply With Quote
Old 06-05-2012, 08:14 PM #16
Class 4 Laser
 
Join Date: Nov 2008
Posts: 5,728
Rep Power: 547
ElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond repute
ElektroFreak ElektroFreak is offline
Class 4 Laser
 
Join Date: Nov 2008
Posts: 5,728
Rep Power: 547
ElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond reputeElektroFreak has a reputation beyond repute
Default Re: Why are diode lasers different?

That has to do with the rectangular cross-section of the cavity. Due to the fact that one dimension (axis) is longer than the other, some of the light traveling within the cavity travels further in one dimension than it does in the other. Because of the effect of cavity dimensions described in my last post, the light that travels in the longer dimension will have lower divergence than light traveling in the shorter dimension. This results in an astigmatic beam, where one axis diverges faster than the other. With most other types of lasers, the cavity cross-section is symmetrical, often perfectly square or circular.

Here's a diagram that might help you visualize what's being described:


You can see that the beam is oval, like single-mode diodes. The cavity is the small rectangle with the V shaped dotted line in it, the length of which is marked by "D". The output facet of the diode is in the front and center of the area called "active layer". You can see that the thickness of the active layer is less than the width of the rectangle that marks the cavity. This is the difference in dimension that causes astigmatism.
__________________
Laser Resources (for n00bs and veterans alike!)

Sam's Laser FAQ (The Laser Bible)

http://www.repairfaq.org/sam/laserfaq.htm

RP Photonics Encyclopedia of Laser Physics and Technology

http://www.rp-photonics.com/encyclopedia.html

ULTIMATE DIY PROJECTOR REFERENCE

http://nqlasers.com/scannerreference...itle=Main_Page

SUCCESS is the best revenge.

Last edited by ElektroFreak; 06-06-2012 at 03:58 AM.
ElektroFreak is offline   Reply With Quote
Reply





Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On











Loading








Green Laser Pointers by Category Blue Laser Pointers by Category Red Laser Pointers by Category
Yellow Laser Pointers by Category Violet Laser Pointers by Category Orange Laser Pointers by Category
Top Laser Pointers by Power - 1 Watt+ Top Laser Pointers by Power - 500mW+ Top Laser Pointers by Power - 250mW+
Laser Pointer Database High Power Laser Pointers Laser Pointer Diodes






Privacy Policy | Advertising Disclaimer | Terms of Use


 


All times are GMT. The time now is 10:23 AM.


Powered by: vBulletin
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO
Privacy Policy | Advertising Disclaimer | Terms of Use
Copyright (C) 2017 Laser Pointer Forums, LLC