Is it possible to communicate with flash through the usb connection and use a rf receiver on the same arduino?is it easy? and how?
What is your "RF receiver" receiving? Async serial data? Button pushes off a car-alarm-style remote?
a signal saying a laser switch has been triggered from a rf transmitter http://www.littlebirdelectronics.com/products/rf-link-transmitter-315mhz
If all you're sending is a logic level, it's dead easy: just look at the examples for hooking up switches and logic signals to digital pins.
If you're going to put a microprocessor at the other end, and have it send ASCII data, it gets a little trickier, because the Arduino only has one hardware UART. There's the software serial library that "bit-bangs" async data, but it's not as good as a real UART, especially for most receiving uses. If your application isn't extremely cost-sensitive, I'd recommend an Arduino Mega, for the simplicity (and improved reliability) of multiple hardware UARTs.