Wide/thick beam laser module

[ricko_uk]

Hi,
I have been trying to find a wide beam laser module with beam diameter around 15 to 20mm wide.

Something like what Big Clive had in his video here:

But the ones I found seem to have the beam distorted (like one of those shown in that video).

I can go up to £ 50 (maybe £ 80 or £ 100 if it is really something with amazing tech specs). Does anybody know where I could find one?

Thank you

[moffy]

Could you please define why 'distorted'/slightly irregular is not acceptable, do you have an end use that requires certain specifications? Laser diodes are usually rectangular in the emitting area so won't tend to scale up to a nice even circle easily. Gas lasers like HeNe tend to have a much rounder emission spot and would scale to a circle better and I would expect the center to have a higher intensity than the edges.

[ricko_uk]

Thank you @moffy,

because for some experiments I want to try to project an image (through a mask) and if I limit the area to a smaller size it would be too difficult to keep the image resolution. Similar to the setup of the bottom right image in the attached picture.

Obviously I can buy professional equipment but that would cost hundreds of pounds or possibly thousands. Those low costs wide-beam lasers already have the collimator optics in there.

Thank you

[ejeffrey]

Laser diodes have significant astigmatism.  You can circularize them with prisms or cylindrical lenses.  It's not going to be perfect and even if it was the beam is going to be strongest in the center and fall off at the edges (ideally gaussian, in reality a lot messier).  If you want uniform illumination of a mask you need to over-expand the beam so that you are only using the center, or use a graded attenuator to flatten out the profile.

[moffy]

So you want a largish beam with even intensity across the width of the beam. Do you need laser coherence and or any particular frequency of light?

[Alex Eisenhut]

because for some experiments I want to try to project an image (through a mask)

Thank you

I have a dollar store laser cat toy with different images, like that?

[ricko_uk]

Thank you all,

@moffy
Yes I need laser coherence. The frequency ideally around 630 (620 to 660 is ok) but it is less crucial. Any suggestions or tips?

@AlexEisenhut
more like using a mask, I think they work differently but I'm not sure. But please do share any thoughts, ideas or suggestions you might have.

@ejeffrey
any suggestions on how to do that without expensive setups

Thank you

[LaserSteve]

Your choices are,  Buy a HENE laser and an up-collimator.  Buy a circularized diode laser and an up collimator.  Improvise, learn a bit about laser  optics, various techniques with Lenses,   and buy neither.

If your just projecting with low coherence requirements, buy a multiimode diode and clean up the beam.

+Thick or FAT beam inexpensive  Asian lasers are for meeting an eye safety specification in low power night club
 effects.  Makes it easier to hit the 2.54 mW/Cm^2  eye safety limit.

Change your search to "FAT beam"  and things brighten up...

The Below is Steve's massive cram course in where to look for diode technology, with Google keywords, links,  and poorly organized because I do not have much time to explain this evening:  There is no such thing as a circular laser diode with a clean TEM mode in production, inexpensively. 

There are cheap imitations, but if you want a TEM00, purely circular mode, your looking at Gas or Solid State lasers.
DPSS green Lasers using Nd:YAG or ND:GVO4  at 532 nm are usually closer to an M^2 of 1  then anything red diode and normally inherently circular, if you want low cost.

Laser diodes emit an ellipsoid, and a noisy one at that.  Single  mode diodes are the easiest to work with, but power clamps at around 150-180  mW for the red ones.

Just because the beam is circularized, does not mean it will have a uniform power profile across the beam, by any means.  The term is "transverse mode structure"

Fiber coupling, circularization using implanted lenses in the diode housing, spatial or external geometrical optics may approximate a circular beam with various properties.  Often we stack diodes in array forms to get nearly uniform non-circular  beams, using polarization combining or "Knife edging" mirrors. That is beyond the scope of this post.
 

Circularized laser diodes or fiber coupled diodes  come from Power Technology, Coherent, Blue Sky Laser or Lasertree...


If you need much more serious performance, ie interferometry or lithography, , as you really are describing a range of performance:

Diode lasers in a temperature controlled mount, and perhaps with Littman Metcalf grating feedback or an internal Bragg grating are OK for holography and interferometer.
Most people build their own.


Usually we just use a normal single mode diode and masking between relay lenses, anamorphic (cylindrical lens pairs or prism pairs )  or a spatial filter for "near Circular". A popular method is a pinhole or razor blades on a magnet as a mode limiter in front of a raw diode package and a large diameter F1 lens as a pseudo-collimator.

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.thorlabs.com/images/TabImages/Elliptical_Beam_Circularization_Lab_Fact.pdf

As you mention masks, and we have no idea how stable a beam you need, well, I'll cover all that.

Everything you wanted to know about screening diode laser sources for simple holography or interferometry is on W's page, and if you need frequency stability there are plenty of articles on Littman Metcalf grating feedback ranging from gluing a piece of microscope slide in front of the diode as an etalon, to elaborate temperature and grating feedback with variable air pressure applied to the diode case for minute shifts in wavelength.  For purely projection applications, this may not matter, but I'll cover stabilization anyways.  Some times for pure projection applications we destabilize the laser and force it to change modes for a homogeneous beam on a long time scale. That too, is beyond the scope of this post.     

http://hololaser.kwaoo.me/argonlaser.html See his pages on single mode diode lasers, especially the mode hop detector with the photodiode.

keywords:  VBG diode laser, diode laser holography,  volume Bragg  grating, Littman Metcalf, circularized diode laser, spatial filter, adjustable collimator., EDCL ,  cylindrical lens pairs, anamorphic prism,  FAC lens, up collimator, adjustable collimator. 

Nine times out of ten when someone tells me they need a very fancy red diode, I have them buy a single mode red, a simple, cheap,  current mode  driver, and appropriate hobby grade glass collimating optics already in a brass mount, then stabilize it with a TEC or current modulation. .  They report back success without buying fancy hardware or making their PI broke.  Just watch for back reflections caused on the optical table.  Then once in a while someone really needs an amplitude or frequency stabilized HENE laser or a diode with Internal VBG, but those are rare individuals.

If you have infinite budget just get a new or used Coherent Obis or something from Power Technology Inc. optimized for transverse mode.  Then upcollimate it.

Again, most people find they can quickly build what they need from Hobbyist and Ebay parts.

DTR lasers comes to mind for the US, and Roithener Laser Teknik for Europe.

If life gets really tricky, articles like  https://physics.byu.edu/docs/publication/597 o
OR:

http://www.submm.caltech.edu/kids_html/DesignLog/DesignLog179/MillerMUSICReadoutDocs/HEMT%20Power%20Supply/Libbrecht%20and%20Hall,%20A%20Low%20Noise%20High%20Speed%20Diode%20Laser%20Current%20Controller.pdf

will help..

One should experiment with low power red diodes and hooking up drivers before trying one of these surplus raw parts:

https://www.mi-lasers.com/product/5mw-635nm-circulaser-laser-diode-5-6mm-dia-2/

Or if your really just projecting:



https://youtu.be/A5sjyEGFOhE

Good luck...

Steve


 ,

[ricko_uk]

Thank you @LaserSteve, lots of useful info.