There are 4 common types of diode laser lenses:
- 3 element
- G2 (short focal) (cutting)
- G7 (similar to 3 element lens)
- G8 (Used in VG-L7x)
The G8 has these specs:
- Optimal focal range: 30-100 mm
- EFL: 8mm
- NA: .2
- Best focal range 70-75 mm
- Smallest laser beam spot: 77 x 130 microns (0.0030315 x 0.00511811")
Briefly about a 3 element laser lens
A 3 element collimating lens w/ AR coating for 405nm – 465nm. It has M9/P0.5 threads that will work with a lot of standard diode housings available. This lens is good for correcting laser beams for long ranges.
Briefly about a G2 laser lens
This lens is the best choice for short ranges, as in an engraving machine. For long ranges please consider 2 or 3 element lenses.
Briefly about a G7 laser lens
The G7 is a second-best high pass single lens but it won’t increase the beam divergence as the G2 does. The G7 has a long focal length just like a 3-elements lens. It’s a well-balanced lens that has the advantage of 3 element lens (very good divergence) and G2 (in terms of power).
Briefly about a G8 glass collimation lens.
Broadband AR Coating 400nm-700nm
This lens is a long focal length single-element glass lens with a broadband AR coating. It has a 90% pass efficiency which is amazing for a longer focal length lens. It does an amazing job of cleaning up stray light around the projected spot with many common diodes caused by the small amounts of uncollimated light escaping the lasing cavity reflecting off things like the edge of the emitter, walls of the module or inner walls of the lens barrel. Like the G2 lens or countless other similar lenses being sold as G-2’s, it creates a reduced spot size while maintaining a 90% pass efficiency compared to the 96% pass efficiency of a G2 lens.
Comparison of Lens Performance
3-element lens (cleanest beam profile, best for low power lasers)
The 3-element lens has a long focal length, low divergence, and clean beam profile but it has a significant output loss.
Advantage Tight laser beam with the cleanest beam profile
Downsides 84% efficiency (1W diode = 700mw using this lens)
G2 lens (best for power)
The G2 is a single lens enabling the maximum true power of the laser diode for rapid close-range burning and engraving.
Advantage 94% efficiency, reduces the beam aperture
Downsides Increase the beam divergence (thickness) and the beam profile
G7 lens(Balanced Multi-Purpose Perfection)
This lens is a cross between the divergence and the power lens. With the G7, the beam divergence won’t increase as it does with the G2 and you will still get very close power of the laser diode.
Advantage 91% efficiency, long focal length and increases beam aperture.