4-86 In a vacum chamber, a thik slab is placed under an array of laser diodes with an output constant pulse. A thermocouple is inserted inside the slab at 25mm from the surface and the slab has an initial uniform temperature of 20 degrees C. the known properties of the slab are k=63.9 W/m K and alpha=18.8*10^-6 m^2/s. If the thermocuple measured a temperature of 130 degrees C after 30 seconds the slab surface has been exposed to the laser pulse, determine (a) the amount of energy per unit surface area directed on the slab surface and (b) the thermocuple reading after 60 seconds has elapsed.