Techhood of China

[Laser57]

If buying green laser diodes from Techhood in China, you might not get what you are paying for. I purchased a dozen "low hour tin pin NDG7475" diodes at half price which were really NDG700 diodes or something less, the divergence was also much greater than the NDG7475 would have produced. It took months until I tried to use one, the seller would not make the deal good as I took too long to find the dishonesty. Normally, at least, in the past they have been reliable, but not for these diodes anymore.

I had been buying from them for years, now very rarely and only for something they can't cheat on. I shouldn't buy a thing more after that stunt.

Edit: added tin pin description as this is how they listed them. This was awhile back, but I haven't forgotten.

[Laser57]

https://www.ebay.com/itm/266387712361

Received two lasers sold by Techhood in China listed as 591 nm, but they both measure 593.5 nm instead of what I ordered. The good news is they worked and both produced 30 mw of output power or more. When testing I found a very small amount of power peaking at about 811.3 nm which kept creeping to a longer wavelength as the module warmed I believe must be the pump diode leaking through.

The following isn't unexpected due to testing without a proper heatsink, but when powered at at 3.65 VDC (3.7 specified max) the two units I received both have unstable output after 30 seconds, reducing output power lower and lower as they warm. A good heat sink should solve the problem, temperature controlled active cooling certainly would.

Not the wavelength specified:

Appears Techhood might be listing all of their yellow lasers as what ever wavelength people might be searching for on ebay looking for hits and selling them all the same 30 mw yellow laser heads. Not a bad deal, I just don’t like expecting and paying for a specific wavelength and getting something different. However, to give the benefit of a doubt Techhood recently remarked to another buyer they don’t have a spectrometer to measure the output wavelength, so it is possible they were sold these as 591 nm. Regardless, the price is LOW for a yellow laser head like this and in my opinion, a good deal.


Above, the modules received from Techhood with 591 nm marked on the bag. Spring soldered to the driver board is negative polarity, the brass body positive.

[absolom7691]

I have had similar problems with Techhood. I ordered several RGB modules from them, listed as 450nm, 520nm, 640nm. What I got was 450nm, 505nm, 640nm. Mint green was not the color I was looking for in an RGB module and was useless for a projector. I like the color and am adding to my collection of wavelengths in my lumia but I'm annoyed that it was relegated to my lumia because the listed wavelengths didn't match what I received.

[Laser57]

Whether from negligence, dishonesty, or inability to know the difference? IDK, but if I were in the business of selling this stuff I'd never purposely do that. I spent a lot on the "NDG7475" diodes which were a far lower output device and different specs than advertised, you would think they would work something out with me to make it right after being a ten year customer, but nope, refused. I shouldn't have even bought these "591" nm devices based on that, but I did. I suppose if people are stupid enough to keep buying, they will keep selling to them. Still, I am happy with these 593.5 units anyway. It's a mixed bag with them, you just can't count on what they say they are offering being correct, in the past they were better.

[clickamouse]

I've bought several of these yellow jobbies, with mixed results.

I replaced the drivers with bigger Chinese jobbies (boy, do I miss Vladimir...) and heat sinked them in massive aluminum holders. I can get around 65mW this way; they are nice and bright when combined with 1W RGB diodes, due to eye sensitivity or something. Using these for lumia on a new project.

Interesting that the 30mw jobs are less expensive than the 5mW ones.
Beam is small and well collimated.

Very twitchy to get up and running - much fiddlement is required. Voltage and driver CV need to be just so to get any action.

And being DPSS, they are very sensitive to temperature, as we found out at 4:00am in Albuquerque during Balloon Fiesta:
https://illuminatuslasers.com/abq.shtml

We had to stuff heat packs into the projector to get it to work.
(This was an effect we called Sun et Lumiere; an audio-driven twitchy thang responding to NOAA-provided audio based on the solar wind. Long story, see website.)

Anybody know of a way to combine these other than knife-edge?

Nice to get another color into our projects, just wish they were more powerful and stable.

...Mike

[Laser57]

How many beams do you want to combine? I've seen PBS cubes used to combine stacks of four knife edged in one polarity and another four in the opposite polarity for a total of eight beams, but they are side by side anyway, only purely coaxial if two are used with a PBS cube and a rotator which I've done with green laser diodes. I'm probably speaking at too basic of a level, but I've been looking into beam combining options too. I suppose a rotator could be used for one of the stacks to make them appear as if four beams side by side when really eight total, if you were looking to combine that many.

[clickamouse]

I tried a cube, but being DPSS, I don't think the beam is polarized.
Didn't work.

...Mike

[Laser57]

IDK, I guess the specs would say. Researching online, all I can find is, it depends on several factors, need someone else to step in, getting beyond me.