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200mW 650nm Red Laser

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Patrick

Wed Feb 09 2011, 11:03PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

TheMerovingian wrote ...

It is due rayleigh (raman is way too low on intensity) forward scattering probably, dust particles appear as small point-like light sources. At these powers the scattering is very strong even at red wavelenghts. My 3.5mW red laser pointer for comparison has almost invisible beam. I would like to build one using a 405nm blue ray laser (they are 150mW nominal), the scattering is stronger at these wavelenghts. I can find one for 12 Euros here in italy.

It is my understanding the rayliegh effect is non-linear vs. freq, is that what you are getting at? I was led to believe that red, orange, yellow are weaky visible green, blue are best acted on by Rayliegh, given constant power.

PM me once you build a laser capable of downing Russian or Chinese fighter planes please.

dmg

Thu Feb 10 2011, 03:54AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627

You are right about rayliegh and blues... but.. with green lasers, although there is less energy per photon, it still appears brighter. as green is at the peak of our visable spectrum.
so a beam of the same divergance, diameter, and power, green VS blue, you will see green as brighter.
This can be seen with beam expansion optics, as most greens have a very narrow beam as its a DPSS system. (532nm diodes exist alright... just at the level of prototypes where anyone who isnt filthy rich can't afford one)

radhoo

Thu Feb 10 2011, 09:25AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Here is a short comparison, between a green 532nm laser and a blue 405nm laser. Both are low power laser pointers, rated at 5mW max.

The green beam is more visible on camera but also for the naked eye:

Regarding the energy level, it is clear the blue is more energetic (E = hc / Î»), here is a little experiment showing the photoelectric effect to demonstrate it:

The left photo shows the green laser illuminating the cathode of a vacumm tube. The right photo shows the blue laser. Notice the multimeter readings.

Patrick

Thu Feb 10 2011, 05:14PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

TY Radhoo, I need a green laser then.

TheMerovingian

Sat Feb 12 2011, 11:12AM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

Green laser is a bit more complicated. It is a solid state laser pumped from external source.

A 808nm diode pumps tje Nd:YVO solid state lasing medium giving approx 1028nm Ir radiation, then a multiphotonic crystal (KTP two photons in, one photon of double energy out) doubles the frequency to 514nm (green). Green laser diodes doesn't exist

dmg

Sat Feb 12 2011, 02:39PM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627

TheMerovingian wrote ...

Green laser diodes doesn't exist

Shun the non-belivers... shuuuuuunn shuuuuunnn...

Yes, currently all available greens are a DPSS system as you said. but green diodes most certainly exist.
they are just in prototype and lab stage. there was a company that developed and published a working prototype, but the name escapes me.
IIRC they are expeceting market introduction ~2012

Its mostly just the regular advancement of technologie, right now we have diodes capable of outputing 2W in a 5.6mm can. its only a matter of time before things get even more powerfull, amazing, and smaller.

(some odd reason, all the cameras ive got capture 445 as purple/violet. its a very pure blue IRL. white ballance adjustments dont help me much either)

Dr. ISOTOP

Sat Feb 12 2011, 03:28PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

TheMerovingian wrote ...

Green laser is a bit more complicated. It is a solid state laser pumped from external source.

A 808nm diode pumps tje Nd:YVO solid state lasing medium giving approx 1028nm Ir radiation, then a multiphotonic crystal (KTP two photons in, one photon of double energy out) doubles the frequency to 514nm (green). Green laser diodes doesn't exist

Vanadate lases at 1064 nm, not 1028 nm.
Building green is either loads of work or loads of fun, depending on your idea of fun

For low (~100 mW) you are better off buying a complete made-in-China system.
If you want serious power without spending enough money to buy a luxury car, you'll have to build your own system.
Big greens are typically pumped by one or more diode bars (a monolithic linear array of anywhere from 20-60 individual emitters), which are available used on Ebay for reasonable amounts of money. You want a bar with a wavelength centered at 808 nm, preferably the 808 +/- 3 nm sort.
There are two types of pumping geometry, side pumped and end pumped. End pumping with a diode bar requires a fiber coupled bar or a *very* (read: don't try building it at home!) complex system of optics. These lasers usually pump a small chip of Nd:YVO4. Advantages: more efficient, better control of beam structure. Disadvantages: requires fiber-coupled bar, not very scalable.
Side pumping uses diode bars pumping the a long Nd:YAG rod from the side, similar to the good old lamp pumped systems. One of the higher powered designs uses a optical waveguides (little pieces of glass that transmit light via total internal reflection) to close-couple the pump light to a water-cooled rod, and surrounds the entire cavity with a ceramic diffuse reflector to homogenize the pump light. Lower powered designs can simply use a 20 or 40W diode bar close-coupled to the rod. Advantages: cheap (no fiber coupling needed), very scalable. Disadvantages: less efficient, thermal issues are a bigger problem vs. end-pumping.
The green is produced by a nonlinear crystal, usually KTP (Potassium Titanyl Phosphate) or LBO (Lithium Borate). These are also available from Ebay. Note that the KTP or LBO has to be appropriately cut for SHG at 1064 nm - nonlinear crystals are *very* orientation sensitive. A random crystal from Ebay may not work. The crystal ends also should be brewster-cut or coated for AR1064/532.
The cavity optics are dielectric mirrors. There are three types of cavity - linear, L/V-fold, and Z-fold. The linear cavity is your typical laser resonator - rear mirror is HR1064, front mirror is HR1064, HT532. The order of elements in the cavity is HR-YAG-NLO-OC. This cavity does not scale well to higher powers and loses a portion of the beam as a backwards traveling beam.
The next type of cavity is the L-fold. The L-fold folds the cavity to lengthen it and recover the backwards traveling beam, leading to higher outputs. The Z-fold cavity, usually used for very high powers, uses an intracavity telescope to reduce damage in the crystal.
For maximum efficiency, you will also need a Q-switch, which greatly increases the SHG efficiency by increasing the peak power of the beam.
Done right, these systems have been known to produce 100's of watts of green.
Koechner's classic book Solid-State Laser Engineering is a very good place to learn more.
I found a few patents of papers that may be of interest (the Laserscope patents, and a couple papers on high-power side-pumped lasers). PM me if you want a copy.

TheMerovingian

Sat Feb 12 2011, 04:18PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

bwang wrote ...

Vanadate lases at 1064 nm, not 1028 nm.
Building green is either loads of work or loads of fun, depending on your idea of fun

Yeah. Sorry for mistake

bwang wrote ...

I found a few patents of papers that may be of interest (the Laserscope patents, and a couple papers on high-power side-pumped lasers). PM me if you want a copy.

Ok. Thank you

I forgot to ask. Funny applications for class IIIB lasers like the red one?

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