Mass Spectrometric Studies of Laser Damage in Calcium Fluoride

Both electron impact- and laser ionization-mass spectrometry have been used to probe the material spalled from CaF₂ surfaces by the fundamental(1.06μ) and harmonic (355 nm and 266 nm) outputs from a Q-switched Nd:YAG laser. We have identified a number of gas phase products, including Ca, CaF and tentatively, CaF₂, and have measured their translational and internal energy distributions.

Our results suggest that while the 1.06μ experiments can be adequately modeled in terms of a single damage mechanism (likely avalanche breakdown), the short-wavelength results suggest the onset of second mechanism, perhaps multiphoton absorption. This is consistent with both the observed bimodal velocity distribution following short-wavelength damage, and with the decrease in CaF vibrational and rotational excitation.