Hello,
I was hoping somebody with a bit more knowledge than myself could help me clear up some confusion / questions I have over 405nm laser diodes. Ever since I joined the laser hobby 3 years ago, I've always had this notion in my head that 405nm diodes were significantly more fragile and prone to death versus blue, red, and green diodes. I feel like I recalled reading this somewhere a while back, but I may be wrong. Some of this stems from the fact that out of the 3 lasers that I have ever had die on me, 2 were 405's. I've also noticed that the 405's often have a shorter rated duty cycle. So if there is any truth to this notion, would somebody be as kind as to explain to me why this is? And one final question, if you don't mind; are direct diode lasers capable of mode hopping, or is this behavior exclusive to DPSS and crystals? I ask because I have witnessed a visibilty/power fluctuation or two in my new Sanwu Guardian 1.6W 405nm, that resembles mode hopping. It only occurred when I pushed the laser too far past its duty cycle, and didn't result in any permanent change to my power output. Any help on these topics is greatly appreciated!
-Nick
Just long story short (I'm just about to get to sleep right now).
My WL Lunar 405 nm (over 500 mW) is quite stable single mode. Very beautiful dot. Due to wavelength very focusable. Nice beam compared to my Arctic. It is about round shape - not like those rectangular dot shapes blues and reds. Compared to 520 nm green (visible TEM33 - TEM22) it is much better beam.
In case of DPSS the modes looks a bit different due to completely different optical cavity design. Still my 405 nm is comparable to TEM00 of DPSS.
It is beautiful laser. I use it for kind of circulatory system of trees (how it was called by one of somehow close person to me) in my art (link in my signature). The wavelength gives you a lot of single photon energy to perform various fluorescence experiments (I created even full rainbows, just a bit of blue was missing).
It's visibility of beam and dot is somehow tricky. You almost see 500 mW like less then (for green) / around the same (for red) 5 mW (as I perceive it approximately), but the power is there. Just shine the dim dot far next to T-shirt (best are light colors, but even black one works somehow) washed in detergent and the fluorescent glow of T-shirt illuminates quite a large area (I use this effect to get some light during laserpainting exposure). Durability - no problem so far. I use this laser quite a long time without problems (in all kind of conditions). Stabile, no (significant) mode hopping observed. These diodes (as mentioned above by the others) are known to be stable. Power consumption is not nearly as my 589 nm DPSS (see signature) and far below 473 nm. I would compare it to be a little less than my red (signature as well) by feeling (but I would need to measure it). Duty cycle is more matter of good heatsink/host, mine is unlimited. WL Spyder host is quite large, but dwarf compared to JL Pro host. See my review of 473 nm - at the end, there is pic comparsion with other lasers I had in time of writing review. This laser is DPSS, and very inefficient one even in DPSS lasers (but it is color of the sky in nice beam) and produces a lot of heat even if of much lower power than my 405 nm. Even this large host heats a lot (405 nm is always almost cold). And 473 nm switch modes if it gets too hot, significant and clear DPSS style TEM01 (never happend such a visible change with my 405 nm). So If you see it like this you will end with 405 nm very efficient and stabile overall. I did not even noticed any significant power loss over the time (more than year of use). Still perfect. And I did with this laser a lot of stuff (used quite often)... What I read, reds were reported for COD (Catastrophic Optical Damage) problems even here on LPF (search for it). I've not seen any reports of 405 nm being burnt by direct window reflecion or so.
And the laser has awesome effects in adition. Especially I like diffraction patterns of seeing single dot as it appears there is a circle of dots around the real dot when shined on specific surfaces. Also you can observe leaving it traces (lasting about a half to one second) of extited fluorescent material (fluorescent paint). And if you have some photoluminiscent material (like those phosphorus stars you can stick on your ceeling and see them glowing after you switch lights off) you might even draw on them. Good to get pointer and play with it.
The wavelength is not good for pointing (you won't see the dot after some distance in order of 10 meters), but definitely great for other purposes where near UV light can be used.
Just keep the danger of low visibility and reduced blink reflex. In other words, even it seems weak, there is much more power than almost other visible wavelength of diodes available. It means take extra care, be safe and have fun with experiments. For pointing and far field experiments get more suitable wavelength.
DPSS lasers are another story. There are significant construction differences as you know, therefore certainly beam characteristics are different. I even posted (somewhere in Laserpaintig thread) some nice mode hopping intentionally induced with my WL EVO (532 nm DPSS). There were interesting things happening in the laser and I got even 4 separate beams. In diodes the modes look differently. There more less look like one beam, but just at closer look you will notice the mode hoping.
405 nm is definitely wavelength for laserists and very specific.
Sorry, for not adding links to give you reference posts (you can find them mostly in my Laserpainting thread somewhere), I'm too tired to do a proper post for you right now.
There is a lot to talk about to answer your questions in more complex way, but I think even this could give you some basic idea.
Edit: Here you can find the mode hopping of my WL Evo I talked about:
https://laserpointerforums.com/f48/radim-s-laser-painting-99824-8.html#post1478645
These experiments taught me a lot about DPSS technology in practical way. I think it is pretty cool as you can clearly see how slightly curved mirrors on crystal can cause more than one beam due to finding more than one (one stable lasing region is desired for TEM00) stabile lasing regions in the gain medium.
In diodes this region is much smaller and behaves differently than in solid state laser - you know, semiconductor stuff.
Do you see how complex devices lasers are here? Even of quite simple construction, the stuff happening there is fascinating (and can be easily understood once you get theory and observe it in reality).
Edit 2: Here the rainbows generated by 405 nm:
It is detail through "crystal" sphere, which refracted the light and allowed to distinguish the rainbow from bright laser paths. Note the rainbows are not laser light, but fluorescence on the organic material on tree surface. Note also missing blue next to 405 nm in the spectre - energy issue. (The green around is from another 532 nm laser.)
