E R(nr) non-resonant reflection

1. Conclusion How tochange the interferenceconditionin the window? very easily, by changing the window temperature For 0.5 mm sapphire window andl=852nm: T  30°C  2 change of the interference (see Jahier et al, Appl Phys B71 (2000), 561 for the use of the "temperature tuning" of the windows for reflection-loss free vapour cells) The raw signal on the Cs D1 line (6S 6P3/2,, F'=2,3,4) amplitude-and-phase diagram amplitude-and-phase diagram F'= 4 F'= 3 The model and experiment agree very well(no fitted parameter!) on the size and the temperature dependance of the spectra. By using a "temperature tunable" window, one can detect at will - the real (dispersive) part - or the imaginary (absorptive) part of the atomic response. S/N is better near the reflection minimum. Changing from one regime to the other is obtained very easily, just by changing the window temperature by a few degree C. Possible application: temperature-tunable locking of a laser frequency on the zero of the derivative signal F'= 2 The experiment Irefl = |ER(nr)1 + ER(nr)2 + Eat|² 1 window 2 dilute vapour -The interference pattern is obvious - The atomic signal is small... (dilute vapour) Twindow 190-230°C off-resonance background subtraction 1 Cs vapour, 3x1014/cm3 852nm laser diode 2 sapphire window diaphragm (rejects fluorescence) - the atomic signal is more evident - (still a "wavy" offset pattern: the subtracted, off-resonance background has a non negligible dependance on the laser frequency) signal = Irefl , vs Twindow &laser Tside-arm=160°C The minimum reflection regime zoom at... derivative raw signal derivative -4p/35 -3p/35 model... ...and experiment -2p/35 -p/35 0 +p/35 +2p/35 +3p/35 +4p/35 SELECTIVE REFLECTION SPECTROSCOPY WITH A HIGHLY PARALLEL WINDOW: PHASE TUNABLE HOMODYNE DETECTION OF THE RADIATED ATOMIC FIELD A. V. Papoyan, G. G. Grigoryan, S. V. Shmavonyan, D. Sarkisyan, Institute for Physical research, NAS of Armenia, Ashtarak-2, 378410, ARMENIA J. Guéna, M. Lintz , M.-A. Bouchiat, LKB, Département de Physique de l'ENS 24 rue Lhomond, 75 231 Paris cedex 05, FRANCE (to be published in Eur. Phys. J. D) the hidden side of the selective reflection signal "ordinary" selective reflection (non-resonnant) reflection at the interface (resonant) atomic response The model ER(nr) IR = |ER(nr) + Eat|² E0 imaginary part of Eat ... is not detected!! ER(at) window n1=1 real part: interferes with non-res. reflected amplitude → detected signal Continuity equations at the two boundaries between the three media: - air, n1=1 - (sapphire) window, n2=1.76 - vapour, n3=1 Maxwell equations for the propagation of the backward atomic field in the vapour (without using the slowly varying envelope approximation) field envelope atomic polarisation ER(nr) non-resonant reflection Eat atomic response n2 window window n3 = n1 dilute vapour dilute vapour Observable = reflected intensity: IR = |ER(nr) + Eat|² |ER(nr)|² . {1+ 2Re(Eat/ER(nr))} How to detect the imaginary part?? Some proposals have been made: ► Brewster incidence (ER(nr)=0) ? (Akul'shin et al, Soviet J. Q. E. 19(1989), 416) the sub-doppler feature of SR spectroscopy is lost; ► multidielectric coating?(theor. work by Vartanyan and Trager, Opt Commun 110(1994), 315)  the coating may be damaged by the atomic vapour ► metallic coating?(Chevrollier et al, Phys Rev E63(046610), 2001)  considerable attenuation of the atomic signal, due to the required metal thickness assuming cell length >> absorption length (no backward beam coming from z=) then =ER(nr) (ordinary reflection from a parallel window , with  = n2kxthickness) = ER(at) (the atomic contribution) (where the tij's andrij's are the amplitude transmission and reflection coefficients) and the backward atomic field is generated by the vapour atomic polarisation: Defining the atomic response by and assuming the absence of saturation and non-linearity, we get (G, GD: homogeneous and Doppler widths): selective reflection with a parallel window (qualitative approach) depending on the relative phase between the two NR reflected beams, two opposite regimes are expected - close to a reflection maximum: No qualitative change: SR signal still displays real part of the atomic response - close to a reflection minimum: then: - Re(Eat) does not interfere with Erefl1 + Erefl2 → not detected - Im(Eat) interferes withErefl1 + Erefl2 → DETECTED! - the Im(Eat)x(Erefl1+Erefl2) signal changes sign around refl. minimum 1 2 Eat 1 2 2 1 ...and experiment model... The raw and derivative signals raw derivative raw derivative reflection minimum 194°C Im(Eat): absorptive j  0 mixed j = p/4 202°C Re(Eat): dispersive reflection maximum j = p/2 211°C mixed j =3p/4 220°C "ordinary" selective reflection "ordinary" selective reflection