A laser that produces a spot of light that is 1.25 mm in diameter is shone perpe

Question

A laser that produces a spot of light that is 1.25 mm in diameter is shone perpendicularly on the center of a thin, perfectly reflecting circular (2 mm in diameter) aluminum plate mounted vertically on a flat piece of cork that floats on the surface of the water in a large beaker. The mass of this "sailboat" is 0.25 g, and it travels 1.7 mm in 75.0 s. Assuming that the laser power is constant in the region where the sailboat is located during its motion, what is the power of the laser? (Neglect air resistance and the viscosity of water.

Explanation / Answer

The energy of a laser typically refers to the output of a pulsed laser and is related to the power output, where the energy (E) is the laser’s peak power (PPEAK) multiplied by the laser pulse duration (t): E = PPEAK x t. The average power of a pulsed laser (PAVG) is the pulse energy (E) multiplied by the laser repetition rate (Hz): PAVG = E x Hz For example, an Excimer laser might have a 10 ns pulse width, energy of 10 mJ per pulse, and operates at a repetition rate of 10 pulses per second. This laser has a peak power of: PPEAK = 10 mJ / 10 ns = 1 MW, and average power of: PAVG = 10 mJ x 10 (1/s) = 100 mW

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