Laser welding is a technique in which a tightly focused laser beam is used to deposit enough energy to weld metal parts together. Because the entire
process can be automated, it is commonly used in many large-scale industries, including the manufacture of automobiles. In order to achieve the
desired weld quality, a particular pair of steel parts being joined must absorb energy at a rate of about 1.1 x 104 W/mm².
A common laser welding system employs a Nd:YAG laser operating at a wavelength of 1.064 µm. At this wavelength, this particular set of steel parts
will absorb about 80.% of the incident photons. If the laser beam is focused to illuminate a circular spot with a diameter of 0.020 in, what is the
minimum power (in watts) that the laser must emit to reach the 1.1 × 104 W/mm² threshold? (Recall that 1 W = 1 J/s.)
W
How many photons per second does this correspond to? (For simplicity, assume that the energy from the laser does not penetrate into the metal to any
significant depth.)
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