This paper describes a novel approach for the suppression of contamination enhanced laser damage to optical
components by the use of fluorinated coatings that repel organic contaminates. In prior work we studied laser damage
thresholds induced by ppm levels of toluene under nanosecond 1.064 μm irradiation of fused silica optics. That work
showed that moderate vapor-phase concentrations (< 15%) of water and alcohols dramatically increased the laser
damage threshold. The data are consistent with the hypothesis that water and alcohols interact more favorably with the
hydroxylated silica surface thereby displacing toluene from the surface. In this work, preliminary results show that
fluorinated self assembled monolayer coatings can be used to accomplish the same effect. Optics coated with
fluorinated films have much higher survival rates compared with uncoated optics under the same conditions. In addition
to enhancing survival of laser optics, these coatings have implications for protecting spacecraft imaging optics from
We have characterized the thresholds for contamination laser induced damage (C-LID) process using toluene as a model
contaminant by varying oxygen and toluene concentrations. In the presence of 300 ppm toluene and nitrogen, the
damage threshold is (7.8 ± 1.9) × 10<sup>3</sup> laser pulses, in synthetic air the damage threshold is (18.0 ± 2.1) × 10<sup>3</sup> laser pulses.
We have found several high vapor pressure molecules that effectively inhibit the (C-LID) process and greatly extend the
lifetime of fused silica optics under high power laser irradiation. With the addition of ~4000 ppm of water, methanol or
ethanol, the lifetime exceeds 1 × 10<sup>6</sup> laser pulses with no damage observed. Possible mechanisms are discussed.
Contamination-enhanced Laser Induced Damage (CLID) occurs when molecular or particulate contamination, present on or in the vicinity of an optical material, leads to accelerated laser power degradation and premature failure. The physical mechanisms that cause CLID are not sufficiently understood to predict the extent to which a contaminant will cause damage. Although standard computational methods can be used to predict the amount of contamination on an optic, the effects of those molecules or particles on laser performance has not been sufficiently quantified. This paper will describe an approach for managing CLID that relies on laboratory studies to understand the relationship between contaminant type or quantity and CLID thresholds. That insight can then be used to guide the definition of cleanliness requirements and the design of material screening tests. Initial efforts to study how mass transport, the movement of contaminants in and out of the laser beam, affects damage rates will be discussed as well.
We have been investigating kinetics issues associated with the development of a new chemical laser in the green based on the b-X transition of NF at 529 nm. The proposed scheme involves energy pooling of NF(a<SUP>1</SUP>(Delta) ) with I<SUP>*</SUP>(<SUP>2</SUP>P<SUB>1/2</SUB>) to form NF(b<SUP>1</SUP>(Sigma) ). The kinetics of NF(a) and NF(X) have a strong impact on the relative populations of NF(X) and NF(b) and therefore play a central role in this system. We have measured the rate coefficients for the reactions of NF(a) and NF(X) with several relevant species including O<SUB>2</SUB>, NF<SUB>2</SUB>, N<SUB>2</SUB>F<SUB>4</SUB>, and I<SUB>2</SUB>. We have also carried out a series of measurements on the energy pooling of I<SUP>*</SUP> with NF(a) by photolyzing mixtures of HI and NF<SUB>2</SUB> at 193 nm to produce H atoms and NF(a). Using a flashlamp-pumped I<SUP>*</SUP> laser, we optically prepared I<SUP>*</SUP> to create a steady-state ratio of [I<SUP>*</SUP>]/[I] during the 30 microsecond(s) laser pulse. This greatly simplifies the kinetics and allows us to extract rate constants for: NF(a) + I<SUP>*</SUP> yields NF(b) + I, NF(b) + I yields NF(a) + I<SUP>*</SUP>, and NF(b) + I yields other products.