HeNe laser, radiance

Radiance of a HeNe laser. We assume that the output power of 1 mW is emitted from 1 mm of the mirror surface into an angle of 4 minutes of arc, which is equivalent to a solid angle of 1 x 10 sr. The maximum radiance in the direction of the laser beam is then L = 10 /(10 10 ) = 10 W/(m sr). This is about 50 times larger than the radiance... 

Qi) Radiance of a HeNe laser. We assume that the output power of 1 mW is emitted from 1 mm of the mirror surface into an angle of 4 minutes of arc, which is equivalent to a solid angle of 1 xl0 sr. The maximum radiance in the direetion of the laser beam is then L = 10 /(10 -10 ) = 10 W/(m sr). This is about 50 times larger than the radiance of the sun. For the speetral density of the radiance the comparison is even more dramatie. Sinee the emission of a stabilized single-mode laser is restricted to a speetral range of about 1 MHz, the laser has a spectral radiance density Zv = lxlO W- s/(m sr ), whereas the sun, which emits within a mean spectral range of 10 Hz, only reaches Ly = l xlO W- s/(m sr ). 

---