If the data is critical to you, turn off the machine it is in immediately and don't do anything further with the disk. If you're serious about this data, don't risk using any programs programs that claim to recover data cheaper than a data recovery company can - you might just inadvertently trash the disk and anything recoverable on it.
Contact a data recovery company and explain your situation. They aren't cheap, but they are usually very swift and can often recover 100% of the lost data.
Going forwards, you might consider getting another external hard disk to use as a backup drive, so situations like this won't be as disastrous in the future.