1 Study of paramagnetic properties of Fe 3+ ions in sapphire for the realization of a cryogenic whispering gallery maser oscillator E. Rubiola on behalf of K. Benmessai, P.-Y. Bourgeois, M. Oxborrow*, N. Bazin, Y. Kersalé and V. Giordano FEMTO-ST Institute, dept LPMO, Université de Franche-Comté, Besançon, France * National Physical Laboratory, Teddington, UK Outline Introduction = WG resonator = WG maser Experiments Conclusions download from http://www.lpmo.edu/~pybourgeois/download/cpem-2006.pdf
Introduction – WG resonator and oscillator WGM m,n,l Low dielectric losses: Q 0 = 1 / tan δ Q L = 2x10 5 @ 300 K Q L = 3x10 7 @ 77 K Q L = 10 8 – 10 9 @ 4 K
Introduction – Whispering gallery mode maser oscillator Resonator @ 4.2 K Fe +3 Gallery mode @ 31.2 GHz Pump Maser @ Storage 12.04 GHz ν 12 = 12.04 GHz WGH 17,0,0 Energy recycling Sapphire Zero dc magnetic field Absorption Line shape of Fe 3+ WGH 17,0,0 low losses Fast relaxation Pump Fe 3+ =[Ar]3d5 BW = 27 MHz @ 31.2 GHz 6 S 5/2 Population inversion 12.038 Frequency (GHz) ν 12 = 12.04 BW » 50 MHz
Experiments – Whispering gallery mode maser oscillator Pump Maser 31.2 GHz , 2 dBm 12.04 GHz , –54 dBm Output power –54 dBm (H-maser –90 dBm) T = 8 K Simple system, as compared to the sapphire oscillator All the oscillator is at cryogenic temperature Theoretical expectation σ y = 1.5x10 -16 τ –1/2 (T=4 K, P=10 nW)
Experiments – Maser stability Low pass ν maser ν maser - ν LO RF Counter 50 dB LO Ref ν LO Ref Local Oscillator Hydrogen Maser Results Temperature control at 8 K No power control, no Pound servo ! H maser Short term limited by H-maser stability σ y ( τ ) σ y (30s) = 2.5x10 –14 t>100 s: random walk τ (s)
Experiments – Paramagnetic parameters : N,T 2 and χ 0 χ 0 dc magnetic susceptibility χ ’ ac magnetic susceptibility T 2 spin to spin relaxation time N ions concentration g Landé factor (g » 2) β Bohr magneton Two sets of measurements: ν ESR = 12.38 GHz » ν 17,0,0 PUMP off: identification of the WGH m,0,0 mode (9<m<20) ν m,0,0 PUMP on: frequency shift measurement ν m,0,0 sat
Experiments – Paramagnetic parameters : N,T 2 and χ 0 ~ after data fitting: For each WG mode: pump off => identify the mode pump on => measure Δν In the literature the ESR width is about 27 MHz => T 2 = 10 ns N HEMEX = 2 ppm REF: Trace element studies in HEM™ sapphire LIGO report M030336-00-M
EXPERIMENTS: Spin-lattice relaxation time T 1 CSO at WGH 18,0,0 frequency = 12.65 GHz Q L ~ 30 x 10 6 over-coupled mode Vosc T 1 = 10 ms @ 8 K
Conclusions 9 Implementation Simple, as compared to CSO The whole oscillator is inside the cryostat No pump power control, no phase control Temperature control at the 8K turnover Available power –54 dBm (40 dB higher than the H-Maser) Short-term stability σ y (30s) = 2.5 × 10 –14 achieved σ y ( τ ) ⋲ 1.5x10 - 16 τ –1/2 expected, at T=4K & P=10nW Paramagnetic properties spin-lattice relaxation time T 1 = 10 ms at 8 K (law: 1/temperature) spin-to-spin relaxation time T 2 = 2 ns qualitative agreement with T 2 = 10 ns in the literature χ 0 = 1 × 10 -9 N = 12 ppb [while N(HEMEX) = 2 ppm] => only a small fraction of the Fe 3+ ion mase download from http://www.lpmo.edu/~pybourgeois/download/cpem-2006.pdf
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