You want to know how to grow herbs, peppermint herb, indoors at your desk. Great, here is how you can do that. Get yourself a desk lamp that will take a standard size bulb and buy a LED Daylight (~5400Kelvin) bulb, or a CFL Daylight (>-6000K) bulb. Get the biggest bulb the lamp wattage will allow. A Daylight bulb will be the best, but a cool blue light in the 6000K range will work too. As for disturbing you, put the lamp behind you and out of the direct line of sight of peoples line of sight. Also, avoid bounce light getting directly in your eyes since that causes eye strain too, you can always cover a surface with flat black paper or paint to reduce reflectively light. I assume you have a cubical wall to help block some of the light. When choosing the light get one that is height adjustable and taller than what you want to grow, mints tend to grow tall.
As for a dimmer switch that is counterproductive to your purpose, however, you could get a timer-switch and have it turn on when no one is in the office.
Remember to pinch/trim you mint religiously to make it thick and bushy, not tall and spindly. It will respond to this attention in a good way. That way it won't get out of control either. Also if you are illuminating the mint from the side turn it 90 degrees every few days to distribute the growth around the plant evenly; better yet just turn it anyway the plant will be much fuller if you turn it regularly.
The essential oil idea is good for home, but people will not appreciate strong synthetic smells in the office. Although you could use oil on a piece of paper on your desk to accomplish the same thing one drop will go a long way. There are many studies that say citrus and mint smell help productivity.
