Lamb-peak

The power P co) depends on the spectral gain profile G a>) and on the absorption profile a (co) of the intracavity sample, which is generally Doppler broadened. The Lamb peaks therefore sit on a broad background (Fig. 2.16a). With the center frequency a>i of the gain profile and an absorption Lamb dip at coo we obtain. 

Fig. 2.16 Saturation spectroscopy inside the cavity of a laser (a) experimental arrangement (b) output power P (co) (c) experimental detection of the Lamb peak in the output power of a HeNe laser tunable around X = 339 pm, caused by the Lamb dip of a CH4 transition in a methane cell inside the laser cavity [221]...

Fig. 2.17 Lamb peak at the slope of the Doppler-broadened gain profile and the first three derivatives, illustrating the suppression of the Doppler background...

These derivatives are exhibited in Fig. 2.17, which illustrates that the broad background disappears for the higher derivatives. If the absorptive medium is the same as the gain medium, the Lamb peak appears at the center of the gain profile (Fig. 2.16b, c). 

Figure 2.46 illustrates the advantages of this technique. The upper spectrum represents a Lamb peak in the intracavity saturation spectrum of the neon line (l 2p) at A. = 588.2 nm (Sect. 2.3.3). Due to the collisional redistribution of the atomic velocities, a broad and rather intense background appears in addition to the narrow peak. This broad structure is not present in the dichroism and birefrin-gent curves (Fig. 2.46b, c). This improves the signal-to-noise ratio and the spectral resolution. 

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. 

Fig. 8.4 Line profiles of Lamb peaks of a HeNe laser at A = 3.39 pm with intracavity CH4 absorption cell (a) pure CH4 at 1.4 mbar (b) addition of 30 mbar He and (c) 79 mbar He [978]...

The combined effect of both kinds of collisions gives a line profile with a kernel that can be described by a Lorentzian profile slightly broadened by soft collisions. The wings, however, form a broad background caused by velocity-changing collisions. The whole profile cannot be described by a single Lorentzian function. In Fig. 8.4 such a line profile is shown for the Lamb peak in the laser output Pl(co) at... 

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]

Since such small splittings can only be observed if the width of the Lamb peaks is smaller than the recoil shift, all possible broadening effects, such as pressure broadening and transit-time broadening, must be carefully minimized. This can be achieved in experiments at low pressures and with expanded laser beam diameters [1117], An experimental example is displayed in Fig. 9.3. 

Fig.7.41a-c. Comparison of different techniques for measuring the neon transition ls2 — 2p2 at X = 588.2 nm (a) intracavity saturation spectroscopy (Lamb peak of the laser output Il cd) with Doppler-broadened background) (b) laser-induced dichroism and (c) laser-induced birefringence [7.72]... 

Fig. 13.2. Linewidth of the Lamb peak in the output power of a HeNe laser at A = 3.39 p.m with an intracavity CH4 absorption cell and different beam waists of the expanded laser beam, causing a different transit-time broadening [13.18]...

Figure 7.41 illustrates the advantages of this technique. The upper spectrum represents a Lamb peak in the intracavity saturation spectrum of the neon line (Is—>2p) at A = 588.2 nm (Sect.7.3.3). Due to the collisional... 

Figure 5 Saturation spectroscopy (A) experimental scheme (B) Lamb dip at the centre of the Doppler-broadened absorption profile (C) Lamb peak (D) difference of the transmitted probe intensity with and without pump.

Doppler-broadened background and yields Doppler-free profiles (i.e. the Lamb peaks) with higher sensitivity (Figure 5D). 

Fiq.l0.24a-c. Intracavity saturated absorption spectroscopy, (a) Experimental setup, (b) "Lamb peak" in the laser output, (c) derivative of a Lamb peak obtained by modulation of the laser frequency... 

If the center frequency o)q of the molecular absorption line is different from the center frequency of the gain profile G(o) - o) ) of the amplifying laser medium, the absorbing sample inside the laser resonator causes a Lamb peak at o)q in the laser output 1, which lies at the slo e of the gain profile (see Fig.10.27). This not only causes a slight shift of the Lamb peak... 

Fig.10.27. Lamb peak and its first, second, and third derivatives in the output Il(u>) of a gas laser with intracavity absorber, when the absorption frequency wq is placed at the slope of the laser gain profile...

F1q. 12,2, Halfwidth of the "Lamb peak" in the output of an He-Ne laser at X = 3.39 ym with an internal methane cell as a function of the CH4 pressure (lower curve). The upper curve shows pressure broadening in an external CH4 cell. The two different intersets are mainly due to the different laser beam diameters in the two cells, causing different time of flight broadening [12.4]... 

Fig, 13,8. Recoil shift of Bennet holes in the lower state population (b) and of Bennet peaks in the upper state population (a). Recoil doublet in the output of a laser with internal absorption cell, generated by the shift of the Lamb dip against the Lamb peak... 

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