How to identify Lasers?

Each diode has its own Po/If (output power to forward current) operational curve and also has its own lasing threshold minimum current. You need a current source tailored to the specific diode you will be using.

I see... and is there any special need to have this external round case?

This diode laser does not seem to have it:

New Mitsubishi 645 655nm 350 500mW High Power Red Laser Diodes LPC 836 1 Pcs PCK | eBay

Its only a protection case (as some pictures in google say) or it might help with something else like heatsinking?

Yes, all but the lowest power diodes have to be pressed into special heat sinking modules or thermal destruction will happen quickly. Most diodes over 30mW or so can't handle more than a few seconds outside of a Heatsink.

But this laser that i've posted is a 350mW and it does not have that round silver protective case around the diode. I think I've misunderstood what you've said.

You should never run any diodes without press in modules. It is not a complete package ready to be powered as is.

Are we talking about the same thing?

I see that there are two basic types of laser diodes which do not come with driver (I will build my own driver). These are:

2X DL 4247 162 Sanyo Laser Diode 650nm 10mW for CD Recording | eBay

and

New Mitsubishi 645 655nm 350 500mW High Power Red Laser Diodes LPC 836 1 Pcs PCK | eBay

the only difference between them is this silver round case on the top. Does it make a huge difference? Can any of these two be powered as they come (without heatsink) or none of them can?

None of those can.

The diodes need to be pressed in to an Aixiz module and then the module needs to be inserted in to a mating Heatsink.

DTR here at the forums has a web store where he sells diodes professionally pressed into modules with an array of lenses and leads attached for modest prices (better than eBay!). I'd go with him as a source. Just google "DTR Laser" to find his shop.

I see.... but I think all diode lasers that come with this module also come with drivers, aint they? And some of them are pretty difficult to remove its driver without damaging it. Is it possible to find lasers inside those modules without drivers? Or should I buy parts individually and then assemble them at home (is it possible?)? Or even buy all together and remove the driver?

What would you do?

DTR sells diodes pressed into modules without drivers.

You have the option to get a driver directly soldered to the diode.

DTR sells them with drivers or without drivers, so you can buy just the diode professionally installed into a module with a lens and lens-holder if you wish.

If I am going to build a 5mW laser, can I simply buy this diode:

2X 5 6mm 635nm 5mW Orange Red Laser Diode DL 3148 034 Sanyo Brand New | eBay

and then buy one of these two:

1pc New 5 6mm T018 18x45mm Industrial Laser Diode House Housing Case Lens | eBay

or

30mm Chrome Laser Diode Housing with Focusing Lens for 5 6mm Laser Diode UK | eBay

And assemble them? This way the final cost would be something around US$ 20,00 at most. Will it miss anything so I could turn it on without damage?

(i am not sure about the first case which is black. It doesnt seem to dissipate much heat...)

FelipeRibas said:

If I am going to build a 5mW laser, can I simply buy this diode:

2X 5 6mm 635nm 5mW Orange Red Laser Diode DL 3148 034 Sanyo Brand New | eBay

and then buy one of these two:

1pc New 5 6mm T018 18x45mm Industrial Laser Diode House Housing Case Lens | eBay

or

30mm Chrome Laser Diode Housing with Focusing Lens for 5 6mm Laser Diode UK | eBay

And assemble them? This way the final cost would be something around US$ 20,00 at most. Will it miss anything so I could turn it on without damage?

(i am not sure about the first case which is black. It doesnt seem to dissipate much heat...)

Click to expand...

Yes that will work, however the silver colored module requires the use of a diode press tool to press-fit the diode into the diode housing part of the module. There is also less heatsinking with the silver module, but at 5mW it shouldn't be a problem.

What is your intended application, btw? Is there a reason you need such a fast rise time? 0.5nS rise time would indicate a general rule of thumb eye-balling of <200MHz modulation bandwidth. That is seriously up there in speed. Not saying that such a rise time would be hard to find in a laser diode that is properly selected, but it just makes me wonder about your application.

I'm about to graduate in computer engineering. So I have to make a final work with all I've studied. This will probably be a robot with some intelligence. And part of this work will be sensing the environment. At first I think I will build a ultrasound system working together with a laser system.

But before all that I will try to do what I wrote in another topic here: rage finder with laser. This could be accomplished with laser modulation (laser pulses) and sensing its reflection. Then I could find this distance with the difference between the laser signal and the response signal. I know this is a very short difference since light travels too fast, but it can be amplified. The problem is with signal accuracy. Since the voltage-controlled oscillator output frequency has an accuracy of +- 3%, then I have to work with very high frequencies to have a good result. Since light time will be anything around nanoseconds, then it would be nice to have this fast response from the diode.


Those problems with the silver colored module will also exist with the other module? What is the maximum power I should use with those modules as is?

As is I would not go over 10mW for those types of modules, but the silver one is designed to be placed inside an industry standard 12mm ID heatsink, the black one is a standalone unit.

For laser rangefinder you're going to need higher output powers as the losses from atmospherics, real-world misalignments, and optics add up to be tremendous. Unless you use a VERY high Q optical filter on the receiver ($$$$) you need to use a very high signal to noise ratio to negate the influence of background light. I found this out when I build the laser communication system for amateur radio; anything further than 40meters needed more than 20mW to get a good S/N ratio, and I didn't even have to worry about a bounce mirror or retroreflector and its inherent losses!

Btw, why use a VCO when a simple crystal oscillator will have much more accuracy and less drift? You can even get temperature stabilized crystal oscillators relatively inexpensively on the surplus market. Working with super high frequencies has the added challenges of handling stray inductances and capacitances on the electrical side of things. You may find that the wire-to-wire capacitance of your driver or LD leads dramatically increases the rise time.

I see. Yes, higher frequencies will be much harder to deal with from all points of view. But it may be the only way to do this. I bought a phototransistor with high sensitivity and its peak sensistivity is around 650nm. I dont think ambient light would be a problem since that's why I am modulating the signal. Then I should treat the response signal with filters to find what I'm looking for. Since the current of the phototransistor will vary and its magnitude will be in uA, I will also have to build a good amplification system.

BTW, if I could sense objects within 10m of distance it will be already wonderful!
Do you think this could work?