Effects of Collisions on the Saturation Behavior of the 6328 ≫ Transition of Ne Studied with a He-Ne Laser

The power output of a single-mode 6328 ≫ He-Ne laser is studied as a function of cavity tuning and for different values of gas pressure. A theory due to Szöke and Javan is used to interpret the results. Two parameters $\gamma$ and ${\gamma }^{\prime }$, which characterize a homogeneous line shape in the atomic polarization to third order, are determined as a function of the total pressure $P$. The results for two different gas mixtures are as follows (in units of MHz/Torr): $\frac{d\gamma }{\mathrm{dP}}=22\mathrm{}\pm 7$ and $\frac{d{\gamma }^{\prime }}{\mathrm{dP}}=58\mathrm{}\pm 13$ for an 8:1 ${\mathrm{He}}^3$-${\mathrm{Ne}}^{20}$ mixture; $\frac{d\gamma }{\mathrm{dP}}=12\mathrm{}\pm 4$ and $\frac{d{\gamma }^{\prime }}{\mathrm{dP}}=39\mathrm{}\pm 9$ for a 5.5:1 ${\mathrm{He}}^3$-${\mathrm{Ne}}^{22}$ mixture. Linear extrapolation of $\gamma$ and ${\gamma }^{\prime }$ to zero pressure yields the radiative linewidth ${\gamma }_N=13\mathrm{}\pm 12$ MHz. An asymmetry $\Delta$ in the frequency dependence of the power output is determined as a function of $P$, with the result that $\frac{d\Delta }{\mathrm{dP}}=2.3\mathrm{}\pm 0.6$ MHz/Torr. The shift of the minimum of the power dip is toward increasing frequency for both mixtures.