The laser diode that you linked to is the read diode, not the write diode. Read diodes are (typically) Red, and are generally terrible for even low power laser pointers. It does, however have supreme consistency, and is a very clean beam.
Most DVD writers use a 405nm Violet laser to burn discs. 405nm lasers are excellent for engraving, as they are easily the most focus-able wavelength of laser you'll find on the market today.
Power is another concern. Especially with the 405nm lasers, you NEED eye protection. So long as you aren't looking at the dot directly, you will not damage your eyes (but accidentally looking at dot is possible). However, you will need the protection to focus the dot. Generally, you will want something that can be used consistently without overheating as far as power goes.
- At 120mW you can burn Items, and the engraving will easily come clean off.
- At 300mW you can start engraving non-black objects, and the engraving is somewhat texturable, and you can barely feel it.
- At 500mW you will need to put 3 INDEPENDENT safety mechanisms on your engraver for it to be legal in the UK and US. you'll have a wide range of things that you can engrave onto at this power level, you may want to have a fan running to cool the material.
- At 1000mW, you're at the higher end of the 405nm spectrum, and is probably your best bet for making a laser engraver. Just wear eye protection, for the love of all that is your eyes. This will engrave close to any material, including unpolished metals, but not glass. Exceptional cooling is needed for this type of diode.
Best of luck!
Will the diode likely be destroyed with just DC current from two 1,5V batteries and no driver?
Bare laser diodes are fairly sensitive to over-voltage and over-current conditons. They can also be quite sensitive to ESD.
Two series AA cells (for example) might have enough internal resistance to keep from burning out a laser like yours (fairly high power). Two D cells might not. YMMV.
Is the point of the driver to only provide a steady current? Could not a suitable resistor do the same trick?
A good driver will also ensure there's no current or voltage spikes on power up and shut-down, and protect against ESD.
What is the point of the third pin on the laser diode?
Many laser diodes are packaged together with a photodiode to monitor the light output (usually from the "back facet" of the laser). This allows hooking up the laser driver in a control loop to achieve constant power output, even if the laser temperature changes, for example.
Typically the 3rd pin is a connection to the photodiode. Usually the laser and photodiode share a common pin (either "common anode" or "common cathode") and the laser datasheet will tell you which way your device is wired.
Is the light supposed to be spread out like that from a laser diode? I also bought a bag of cheapo 5mw laser diodes, that are mounted in a small brass housing and appear to have a simple driver attached. Would this housing be enough to focus the beam?
Bare laser diodes tend to emit light in an cone of 30 degrees or more half angle. This angle can be very different measured "in-plane" and "perpendicular" to the top surface of the laser chip.
Some laser diodes are packaged with lenses to collimate the beam so that it has less spread.
The datasheet for your device will tell you the expected emission angle.
Finally, in the case that I do need a driver to set this up correctly, would something like this do the trick?
The driver you linked looks well matched in terms of current and voltage capability.
Whether it provides adequate ESD protection, soft-start, etc., is not clear from the E-Bay listing.
Final Note: 380 mW is more than enough laser power to cause permanent eye damage in case of an accident. Be sure you understand the risks and choose appropriate safety precautions before working with this device and work safely.
Best Answer
Fabry-Perot laser diodes are lasers whose mirrors are simply the flat cleaved surfaces at the ends of the laser chip.
Distributed feedback (DFB) laser diodes are lasers that have a grating structure in the cavity that produces multiple reflections throughout the cavity. This leads to narrower linewidths than are produced by FP lasers.
(Image source: Laser Focus World)
Another type you didn't ask about is the Distributed Bragg reflector (DBR) laser. A DBR typically has two separate grating regions, on either side of the gain region. They're usually distinguished from the DFB because the grating doesn't overlap the gain region, although there is some grey area and the terms are not always used consistently.
(Image source: US Patent #6638773)
Where FP, DFB, and DBR types describe how the longitudinal reflections that provide laser feedback are produced, the designation gain-guided describes how the mode is confined in the transverse dimensions. In a gain-guided laser there is no waveguide patterned between the reflective structures (end facets or DBR regions). Instead, we rely on a narrow region where current is injected to maintain the transverse mode.
This works mainly because any transvese modes that don't overlap the injection region will see much lower gain and so won't lase.