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The main objective of this work was to determine the extent to which lasing on the overtone suppresses the gain on the fundamental transitions P1(4-9) and P2(4-9) as a function of media saturation on the overtone. This was accomplished by a comparison of the residual fundamental gain (RFG) data obtained at three different levels of media saturation with the corresponding zero power gain (ZPG) data. Comparison of the residual fundamental amplification ratio (RF-AR) data with the zero power amplification ratio (ZP-AR) data indicated that the gains of the low J lines P1(4-6) and P2(4-6) were suppressed more than the gains of the high J lines even through their upper or lower levels were not directly involved in overtone lasing. Analysis of the HF mole/mass ratios calculated by a rotational nonequilibrium computer model, ORNECL, showed that the fundamental gains are determined by three independent mechanisms when lasing occurs on the overtone. The first mechanism is the `direct lasing effect' that depopulates the v equals 2 states and populates the v equals 0 states that are directly involved in overtone lasing. The second mechanism is the `rotational relaxation effect' that reduces the rate at which the low J v equals 2 states are populated and increases the rate at which the low J v equals 0 states are populated. The third mechanism is the `collisional deactivation effect' that reduces the rates at which the HF(O,J) and the HF(1,J) states that are not directly involved in overtone lasing are populated by the various collisional deactivation processes that transfer molecules from the high J v equals 2 states (that are involved in overtone lasing) to these lower energy states. Further analysis of the HF(v,J) concentrations and the ZPG and RFG calculations indicated that rotational relaxation is the primary mechanism responsible for the suppression of the low J lines whose upper and lower levels are not involved in overtone lasing.
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