I have always been a fan of Light Amplification by Stimulated Emission of Radiation.

Laser pointers are like flashlights, but cooler. The ability to place a pin-point light source of monochromatic light on any surface from a great distance is just super neat, to me. And the mechanics behind the operation of lasers is fascinating. Even more interesting: we've come up with about a dozen different ways of producing laser light, each with differing uses, properties, pros and cons.

Background

As a kid, I thought all lasers were just red. Most toys with lasers in them used some form or another of the classic 635nm red diode laser module with <5mw output power for child eye safety. The first time I saw a non-red laser was at some science presentation during a class field trip to the local Natural History Museum; I don't remember what the woman was presenting about, but she had a brilliant 532nm GREEN laser pointer that she used during her presentation and much like the beam itself, that was all I was focused on the entire time.

After I realized that it wasn't all just Hollywood magic, acquiring laser pointers in various colors and became a goal of mine; I wanted to collect all of the pretty flavors of lasers. I even made a few laser pointers from modules I got out of broken toys and electronics, and random scraps. I thought they were the closest thing to a sci-fi prop a kid could have, IRL.

The Cyan Laser Pointer

As I've gotten older, stuff like this has become less important to me, but occasionally, when some new technology becomes available I still can't help myself. Recently, 488nm cyan laser pointers, while still uncommon, have become affordable (<$50). I've gotten a few different 405nm 'blue' laser pointers before, but that wavelength is closer to the ultraviolet, is on the edge of the visible spectrum, and appears closer to purple than blue. Apparently, the new cyan lasers are DPSS (Diode-Pumped Solid-State) lasers that work similarly to green lasers in that they have a diode laser that pulses IR light very fast and pumps a YAG crystal lasing medium which re-emits the laser light in the visible spectrum as cyan light. Intrigued, I got a relatively inexpensive cyan laser pointer off eBay from a Chinese seller, but I was not expecting a certain flaw in the design.

As with larger laser pointers I have bought in the past, I was expecting this new one to accept either several AAA batteries or a single 18650 rechargeable lithium battery. The eBay listing did not mention the battery type accepted so I had assumed it would be one of the two since both are pretty standard in these types of devices. This was not so with the rare cyan laser pointer.

It had been designed to accept some equally-rare battery that was slimmer and shorter than an 18650 but much fatter and slightly longer than a single AA battery. I still do not know what type of battery it was supposed to take since one was not included with the device (though it really should have been, given that the type was not obvious or common) and the seller would not respond to my messages.

After connecting it to a power supply to see that it actually worked, I was impressed by the beautiful blue-green beam enough that I wanted to make it work. I decided to modify the laser pointer housing to accept a standard 18650 battery that I had laying around the house; a relatively standard rechargeable battery among flashlight and laser pointer enthusiasts.

The diameter of the battery compartment in the original housing needed to be widened by only about 2mm but it needed to be much deeper for the longer 18650. Another thing I didn't like about the original design was the lack of a momentary push button that could be easily thumb-operated. The original housing was probably adapted from a simple flashlight design where one would only want to turn it on or off for long periods of time, thus it only featured a single toggle-style push button on the end. I like to be able to operate a laser pointer in short bursts as I use it to, well, point things out; I don't want it on constantly as that doesn't do me any good. I had some nice metal SPST momentary push buttons laying around from another project, so I decided to target one of those as they were quality and tactile.

I decided on a 3-step approach to the project:

1. Modify the battery compartment on the lathe.
2. Design and 3D-print an extension tube for elongating the battery compartment and adding a switch housing for a momentary push-button.
3. Reassemble the original laser pointer with the modified printed part and push-button spliced in the middle.

Machining

Luckily, this project only needed some light machining and since all of the features are round that means it's lathe time. I performed 3 main operations: a parting operation to cut the housing in two, a facing operation to even up the cut surfaces, and a boring operation to widen the internal diameter of the battery compartment:

After the machining was complete, I was able to fit an 18650 battery all the way through the battery compartment:

Modeling

With the original housing machined to spec, I took measurements of all of the parts and modeled all of the components that I planned on using in CAD and assembled them virtually. Through a process of trial and error, I came up with the following design:

I would print the yellow part in the diagram and reassemble the laser pointer, soldering the new momentary push-button in-line with the cathode contact to the battery compartment and the laser module's VCC pin. A length of wire would travel through a bypass channel printed into the part and make electrical contact with both the laser module half of the original housing and the battery compartment half, completing the ground circuit to the anode of the battery compartment; this would also leave the original toggle-button end-cap in the circuit, allowing it to be used as an arm/disarm switch.

I was unable to get the final design done in one go this time and went through a couple of prototype phases. I printed all my prototypes and the final version in PETG since it has good layer adhesion and durability properties, but is also available in nice bright colors.

Assembly

Fully assembled, the new laser pointer is much improved, accepting the 18650 battery and making good use of a thumb-switch. I also printed a little TPU cap to slip onto the end with the laser aperture when not in use; it will hopefully keep dust out of the laser pointer body and off the optics:

The form more closely meets the function with the newly added button on the side. I added ridges for grip and a serrated end for styling. The button is slightly raised while the body surrounding the button has a depression all the way around to provide a place to naturally rest the index finger. The final assembled device feels nice and solid in the hand:

The biggest challenge of this project was soldering the new switch into the plastic housing since a fine tip soldering iron was needed to operate without melting the housing itself. The ground connection wiring was also fiddly.

I am very satisfied with the way this short project came out and hope the device will hold up to some wear and tear. I sometimes take things like this on outdoor excursions to help with astronomy and also to point features out while hiking and climbing, so we will see if the design is rugged enough.

Thanks for reading!
~Joseph

Links

• I used this site to find the right RGB color codes to correspond to different wavelengths of light while writing this post.