Problem 63. 64 Martian CO, laser. Where sunlight shines on the atmosphere E = 0.289 eV of Mars, carbon dioxide mole- cules at an altitude of about 75 km undergo natural laser action. The energy levels involved in the action are shown in Fig. 40-26; population inversion occurs be- tween energy levels E, and E. (a) What wavelength of sunlight E = 0.165 ev E =0 excites the molecules in the las- Figure 40-26 Problem 64. ing action? (b) At what wave- length does lasing occur? (c) In what region of the electromag- netic spectrum do the excitation and lasing wavelengths lie?

Check Your Understanding A sodium atom nukes a transition from the first excited state the wound state, emitting a 589.0-nm photon with energy 2.105 eV. If the lifetime of this excited state is 16108s, what is the uncertainty in energy of this state? What is width of the corresponding line?

Give an example of a physical entity that is quantized. State specifically what the entity is and what the limits are on its values.

The rate at which solar wind particles enter the atmosphere is higher during the day than at night, yet the intensity of the auroral emissions remains high well after the Sun has set. Can you suggest a means by which the atmospheric molecules might be able to radiate long after the period of collisions with charged particles has ended? (Hint: How long does it take a typical atom to radiate from a normal allowed energy state? How could this time be lengthened?)