I do not know what type motor your RAS uses, but there are two types of electrodynamic braking possible depending upon motor type.
If it is permanent magnet motor then it will generate power when unpowered and you can short the lines (experiment with low value power resistors first as a dead short may result in too much braking torque). You may be able to do the same for a universal motor but it would require that the field retain sufficient magnetism to generate power, otherwise power will have to be provided to the field coils (to magnetize them) to allow the motor to generate power so that it can be stopped.
If it is an induction motor then it can be braked by passing a current limited low voltage DC current into the unpowered motor. The rotor will then attempt to align with the now stationary magnetic fields in the stator, creating a braking force within the motor. Start off with a modest voltage and current to begin with and stop the current as soon as the blade comes to a stop. If you are too aggressive or leave the current flowing uninterrupted you can either overheat the stator windings or, if far too much current is used, you can create such a strong braking force that the motor or equipment is damaged from the sudden braking force.
You would have to experiment with the above to find out what works for your setup, but only attempt such if you are competent working with electrical as you will be tinkering with exposed line voltage (120/240) while experimenting. You must also ensure that things are properly interlocked so as to ensure that the braking system can never be activated while the motor is energized.
You could also experiment with Lorenz braking using an electromagnet with the two ends of the magnet wrapping around to each side of the blade. However, a typical saw blade may be too thin to accept the heat from the induced eddy currents without overheating.
Or you can simply keep a block of hard scrap lumber around to make one last "cut" after powering off to stop the blade, just do so safely.