Inverse Lamb-dip

Lamb peaks (inverse Lamb dips) at the line centers of the absorbing transitions (Sect. 2.3). The line profiles of these peaks are determined by the pressure in the absorption cell, by saturation broadening, and by transit-time broadening (Vol. 1, Sect. 3.4). Center frequency coq, linewidth Aco, and line profile Pl(co) are measured as a function of the pressure p (Fig. 8.2). The slope of the straight line Aco p) yields the line-broadening coefficient [977], while the measurement of coo p) gives the collision-induced line shift. 

The absorption of the laser is proportional to the population difference AN = Ni — Nk. This difference has two maxima at laser output therefore exhibits two Lamb peaks inverse Lamb dips) (Fig. 9.2c) at the laser frequencies [Pg.477]

Most measurements up to now have been performed with He-Ne lasers on visible transitions [12.1] or on the 3.39 ym line [12.2] with absorption cells inside the laser resonator. In the infrared region CO2 lasers have also been used [12.3]. The laser output lL(tJ >) is monitored while the laser frequency w is tuned across the Doppler-broadened absorption line and the Lamb dip at the center of the absorption profile occurs as a peak in the laser output. The line profile and the center frequency wq of this inverse Lamb dip are measured as a function of pressure in the absorption cell. Figure 12.2 shows the half-... 

The Lamb dip in the distribution An(v ) of the population difference An = n - (92/92)1 2 appears not only in the inhomo9eneously broadened absorption profile a(v) but in case of inversion (An < 0) also in the 9ain profile -a(o)) of an amplifyin9 medium with an inhomo9eneous linewidth. If the frequency of a sin9le-mode 9as laser is tuned over the Doppler-broadened 9ain profile, the output intensity shows a dip around the center frequency wq [10.30]. This Lamb dip in the laser output can be used to stabilize the laser frequency to the center of the qain profile (see below). 

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