There is a product called Window Security Film which is a thin (a couple mm) film that adheres to the window and makes it exceptionally difficult for someone to break. Many lock smiths/security companies can install it. Here's a video of it in action: http://www.youtube.com/watch?v=vYdVK3BqPfk
One of the biggest "problems" with it however is that because it's invisible, people will still try to break the glass. For this reason, often it is installed along with window bars since this provides a visual deterent, but they are pretty ugly for residential installs.
If it is in a frame 1/4" glass will be sufficient. Your options for glass will be tempered glass or laminated glass because of it's proximity to the ground.
Tempered glass will break into very small pieces like a car window for a door. Tempered glass is stronger than normal glass.
Laminated glass will break like a car windshield. It breaks normally but it is two pieces bonded together with a plastic. The plastic prevents most injuries as well as the mess from breaking. Laminated glass is more often used for safety/security applications.
Although 1/4" is suitable for the application, I myself am always weary installing it as an interior partition. My family business has built all glass offices in buildings and we use 3/8" tempered glass. 3/8" Tempered is extremely difficult to break. When you get up to thicknesses that large as far as cost goes the difference between 3/8" and 1/2" thick glass isn't very significant.
If you go with a thicker size be sure that your trim is strong enough to withstand an impact of the weight of the glass, the weight of a person, and the velocity they are traveling. This is due to the fact that it is more likely to break from breaking out of its frame and falling down, especially in wood.
If the beams are not structural I would recommend you use a router to create a slot in each beam deep enough to slide the glass in far enough to place it where it needs to go and then slide it back towards the other beam into the slot you created there. This is commonly done with metal storefronts and is called a flush glaze.
Best Answer
This is a 'Glue Chipped' glass rather than a pattern. Each pane of glue chipped glass is effectively unique due to the process. First the glass surface is sandblasted. Then glue is applied, which adheres to the sandblasted surface. When the glue is removed it pulls away some of the glass surface leaving a uniquely 'chipped' finish. Double chipped glass undergoes the procedure twice but requires a thicker glass because chipping will obviously weaken the strength.
Glue Chipping was often used to create signage for shops and bars by using a pattern stencil during sandblasting. Geometric designs were also created this way.
Some more examples and info on my blog here - (I / we dont sell old glass btw, its content only, and my own research) https://sashwindowspecialist.com/blog/usa-old-textured-window-glass-id/
Simon