Old 11-27-2010, 06:08 AM #1
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Talking 25mm DPSS green modules for DIY- Information thread.

With most DIY green builds on this forum, most use the standard 12mm brass modules. Even those are physically limited to only 150-200mW (depending on the make and model of the module), these modules are the only ones seen here. Even kit sellers don't offer DIY green kits for anything other than the standard 12mm modules. But what if you want to go higher, or want better stability?

Behold, the 25mm green module. A de facto form factor (no 'proper' specifications as found with 12mm modules), these are commonly found in higher-end portables (such as the RPL and PGL-III* units). The modules themselves are also modular, consisting of a detachable laser cavity (left) and the driver block (middle). The 25mm designation refers to the diameter of the laser module holding the cavity, and although more or less consistant, may vary.



The laser cavity (left) is often detachable and interchangable with other drivers (which may offer features such as APC or thermal protection), while the driver block (otherwise known as a pill) features a clicky on-off button and an emission indicator LED. The positioning of the switch and LED is consistant across all modules, allowing modules to be easily exchanged between hosts quickly.

The laser cavity itself has a C-Mount pump diode which attaches to the base of the cavity for optimal heatsinking. The cavity components (gain medium and KTP) are also mounted on seperate copper or brass disks, which reduces the effects of thermal stress and allows for greater stability at higher powers. Unlike 12mm modules, there is often an independant output coupler, which is mounted on a seperate disk, away from the cavity components. A combination of these factors (larger crystals, seperate crystals and powerful pump diode) allow for greater stability and hgher operating powers.

Perhaps the best part is the fact that it still runs off a single 18650 battery. Even when using a 3W pump diode, current draw is still within acceptable limits and can still be adequately supplied from a single 18650 battery.

As there is no fixed dimensions for these 25mm modules, the diameter and length of the laser cavity may vary slightly as a result, with some cavities being significantly longer than others. The diameter can also vary, often by 1mm. Although not important, this can affect heatsinking and performance (despite this, there is often an air gap between the module and the host in many portables.



The retaining ring (wider raised part on the driver block), however, is consistant in size. As a result, the same driver blocks an be made to fit any host that once used a 25mm module.

The spring on the rear of the driver block is the negative contact, while the aluminium body of the driver block is the positive contact. Electical contact is often acheived via the screws used to secure the driver block to the host, especially at currents where direct contact is not enough and where a proper contact is required between the module and the host.

The majority of these modules also require a final output lens- the output from the module is still somewhat divergent. This lens is usually a long focus length lens, fitted slightly behind the aperture. Although an extra external lens may be more hassle to work with, it allows the modules to be focusable.



In the above photo (taken from O-Like), you can see the mount for the final output lens on top of the module. Normally, the module alone looks like this:



Although it may seem like a large amount of work to DIY a laser with a 25mm module, it is the only option, especially at higher powers (>200mW) or where stability is required. Once established, however, they should become much easier to work with (especially when all the measurements and technical data is readily available).

For the few who dare, a pump diode replacement may even be fesible- considering that the drivers can handle 3W pump diodes, while the crystals themselves much more.

It takes a lot to go out there and try something new- but the returns will be well worth it, both in terms of personal gain (have your own custom 300+mW green laser) and for the community.

Here's a list of sellers known to carry 25mm modules:

O-Like- available in powers up to 400mW. These modules come with an external final output lens which is mounted on top of the laser cavity. This lens can be unscrewed and removed.

OdicForce- 250mW, requires final output lens

LVIYLASER~- Power unknown, requires final output lens

Viasho- You will need to contact them directly, they may supply modules (both 532 and 473) to the general public.

CNI*- A variety of models available up to 800mW, requires final output lens and driver. Available in both blue and green.

*Although the PGL-III and PGL-III-C series use a propreiatary driver board and driver mount, the module used conforms with the 25mm form factor. As a result, it is possible to take the modules from PGL-III and PGL-III-C units and mount them onto standard 25mm driver mounts. The drivers are held in place with a plastic retainer, and a custom metal retaining ring holds the module in place. The bare 25mm cavities are available for order direct from CNI, under the product line PGL-H. As with most other modules, these will require a final output lens.

~So, I figured these guys aren't exactly liked around these parts. But still, worth a mention, as not many stores (reputable or not) carry these.


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