Well, you are asking a lot, gotta tell you that. 400mW requires A LOT of power and more important, A LOT of heat dissipation. Hence the huge size of the Hercules. The smallest you can get ~400mW in that I know of would be one of the optotronics RPL lasers. They are significantly smaller than the Hercules and run on a single 18650 li-ion rechargeable battery.
If you are interested in such a laser, I can sell you a Prometheus 400mW - they are RPL equivalent lasers made with the same parts by the same manufacturer. I sell them for less, but I technically can't call them RPLs, so they're the Prometheus series
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If you're looking for smaller than that, unfortunately you're gunna have to compromise. I think you want a pen-size 400mW greenie, but unfortunately that's not possible. The strongest pen-size greenies on the market are the 150-175mW CNI black/gold lasers like those sold by novalasers or myself.
Sorry for the bad news :-/. Feel free to send me a PM, e-mail (pseudonomen137@gmail.com), or give me a call (+1 972 5356177) and we can discuss your needs and possible options. Honest I'd love to personally get you a good deal on one of my own products, but even if it means referring you to another company, I'll try my hardest to find you a deal.
