Review of cheap $35 532nm Laser

[andy]

Wanted to offer this review of a cheap laser. I got it off Amazon, however I found similar units on Alibaba Express (probably where the Amazon sellers get them).

To Luc's comment about scalability of using this, I see Alibaba suppliers claiming 1million+ units per month production ability. That said I'm sure these units will come and go and so it's a moving target if you are buying them one at a time. But anyway wanted to go into detail of this one:

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Unit Description

Here is the listing:

The listing says "12V Green Diode Lasers 532nm Laser Module Dot with TTL 0-30KHZ & Fan Cooling - Long Time Working"

* Wavelength: 532nm, Output power: 95-120 mW
* Operating voltage: DC 12V, Operating Current: <500mA
* Modulation frequency: TTL 0-30 KHZ
* Reverse polarity protection: Yes, with automatic identification of positive and negative
* Laser Module Size:74 x 30 x 30mm , Circuit Board size:71.5 x 35 x 20mm

The unit I received had the circuit board attached to the unit through a screw, but otherwise looks the same.

Controlling power

The reviews were helpful for example this one:

or you folks that are wondering about controlling this PWM, you don’t need a schematic. Look at the board Silk screen next to the Red and Green connectors on the fan power side. This unit is designed to handle two lasers, a Red one plugs into the Red connector that is next to the Green one the Laser power cable is plugged into. The two empty Red and Green connects ( next to fan connect) are the TTL inputs. Looking down on top of those two empty sockets, with the notch side away from you, the right pin on both of these is Ground. The other pin, on both has a pull-up resistor to turn both lasers full on, when NO TTL signal is there. When your TTL signal is present, the left pin of that connector will be pulled low or high to the 5V TTL signal, and if it’s low, laser turns off, if it’s high the laser will be on. The TTL will in effect be turning laser off and on, according to your TTL control

I tested with a signal generator (One titled "1HZ-500KHZ DDS Functional Signal Generator, Seesii DDS Function Low Frequency Signal Generator Sine/Triangle/Square/Sawtooth Waveform") and it seemed to work! I was a little confused about how the ttl works, it seem that the power of the signal is what controls it not the frequency at least in my testing. The laser board also has a little LED which shows the TTL signal and strobe to match the rate if you turn it low enough.

Frequency output

I got this result with an exposure time of 50ms.

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Power output

I don't own a laser power meter, but I disconnected the fan and measured 1.5 - 1.6 watts of wall power. This translates to roughly 100-300mw of power depending on the efficiency of the laser. I wish I could be more precise then that, but that at least roughly matches the description

Safety other warnings

Some of the reviews mention this, and there are youtube videos on this topic but there are warnings that these very cheap lasers lack an IR filter. So it's important for safety to have laser safety goggles that block IR (800+ nm)

My conclusions

Certainly you aren't looking at a precise scientific instrument with these ones, but I am interested to see how far you could get with it. If you don't need precise resolution with spectra, something like this might work.

I am a little worried about promoting these in that low cost instruments are often purchased by kids, students, schools, novices, and other environments that may not understand the safety of high powered lasers (especially that IR blocking comment above).

I will update later if I end up trying this to get raman spectra.

[Luc]

Nice report Andy!

If you start digging into the world of laser for demanding applications like Raman or interferometry, you will want to invest in a high-resolution spectrometer like the one I built : https://www.thepulsar.be/article/high-r ... ectroscopy

With it, you can investigate the current (and temperature -- if available) settings that will give the best performance. I'm currently looking into that with the CPS532 from Thorlabs (just made some preliminary experiment yesterday!). In the case of Raman, a spectral width of ~0.2 nm start to be limiting and most cheap lasers are in the range 1-2 nm. When I talk about scalability it's more in that regards btw because these lasers are absolutely not tuned for narrow linewidth operations. By accident, you may buy one that is super sharp but 100+ (I'm putting some random number) that will be terrible.

Short story but I was talking with people from university of Liege and the best affordable Raman laser they found was a 30€ one from a laser show at some hard discount shop nearby -- ultra narrow band! That doesn't mean, however, that all of these laser show gadget were that good obviously. But "yes" it is possible to get very good performance for a tight budget!

It's a very tough question for a project that people can replicate; because it's possible to get something that is cheaper but that requires more tuning and not everybody is comfortable with that as some people just want the thing to work out of the box. Nonetheless, I'm now 100% convinced that we should answer both needs (cheap & out of the box versions).

Maybe I could make a CAD w/ baseplate & assembly instructions for the high performance spectrometer setup ?