Analysis of hyperfine interactions in NMR studies of Pr skutterudites

The splitting of NMR signal, which is analyzed in terms of the invariant hyperfine coupling between the nuclear spin and the multipolar moments of magnetic ions, gives important information about the multipolar ordering. The NMR splitting of P nuclei is analyzed for the low-temperature phase of PrFe₄P₁₂, whose nature has been controversial. Two scenarios are examined: one is a modulation of the hyperfine coupling caused by the antiferro-quadrupole (AFQ) ordering; another is the hyperfine coupling due to a monopole-type ordering.     

Control of the photodissociation of CsCl

A femtosecond UV laser pulse is used to resonantly excite CsCl molecules from the ionically bound ground state to the first excited repulsive state. The excitation leads to the dissociation of CsCl. After a certain time delay a visible (VIS) femtosecond laser pulse interrupts the dissociation process by resonantly de-exciting the molecule back to the ground state. According to the Tannor–Rice control scheme, the fraction of dissociated CsCl molecules is controlled by changing the delay time between the two fs laser pulses. The processes involved are investigated theoretically and experimentally. Based on the results, a self-learning system has been realized, which is able to control the dissociation without any a priori knowledge of the molecule. Received: 2 December 1999 / Published online: 24 July 2000     

Magnetic properties and magnetic entropy change of amorphous and crystalline GdNiAl ribbons

The structure and magnetic properties of amorphous melt-spun and subsequently crystallized GdNiAl ribbons were investigated. An amorphous phase was formed after the quenching process by melt spinning with a copper wheel having a surface speed of 30 m/s. A hexagonal phase with lattice parameters a=7.023 ? and c=3.916 ? was formed in the GdNiAl ribbon after annealing above its crystallization temperature. Magnetic entropy change was calculated directly from isothermal magnetic measurements. The results show that both the amorphous and annealed samples have a high magnetocaloric effect, indicating that these alloys can be considered as candidates for magnetic refrigeration applications. Received: 14 August 2001 / Accepted: 18 September 2001 / Published online: 23 January 2002     

Iodine hyperfine structure and absolute frequency measurements at 565, 576, and 585 nm

The hyperfine structure splittings of the P(10)14-1, R(15)14-1, and R(99)15-1 transitions at 585 nm, P(62)17-1 at 576 nm, and P(80)21-1 at 565 nm in ¹²⁷I₂ are measured by heterodyne spectroscopy using two dye lasers. In addition, the absolute frequencies of the hyperfine components P(10)14-1 a₁₅ and P(80)21-1 a₁₀ are determined using a self-referenced frequency comb. These frequencies are used in an experiment testing relativistic time dilation by laser spectroscopy on a fast ion beam.     

Sensitive birefringence measurement in a high-finesse resonator using diode laser optical self-locking

We demonstrate a new method to measure weak birefringence of dielectric mirrors with excellent spatial resolution and sensitivity (<10^-7 radians). We exploit a well-known optical feedback scheme for line-width narrowing and frequency locking of a diode laser to a high-finesse cavity. Feedback comes from the intracavity field which builds up at resonance, selected by its change in polarization with respect to the incident field. This change, due to the residual birefringence of the cavity mirror coatings, was already exploited for birefringence measurements using an active laser-locking scheme. Here we measure the optical feedback rate as a function of rotation angle of one of the cavity mirrors (around the cavity axis). A stable feedback signal is obtained since the laser, as soon as it locks to a cavity resonance, effectively behaves as a monochromatic source. By fitting the data with a theoretical expression, we determine quantitatively the local birefringence vectors of both mirrors, which are around 10^-6 radians. Our scheme is simple, works with cavities of very high finesse (F∼10⁵), and is promising for measuring birefringence in gases induced by external fields. Received: 18 July 2001 / Final version: 14 March 2002 / Published online: 8 May 2002     

An all-solid-state tunable 214.5-nm continuous-wave light source by using two-stage frequency doubling of a diode laser

3 and β-BaB₂O₄ crystals. The power of the generated 214.5-nm light amounts to more than 100 μW. This light source will be used for laser cooling of Cd⁺ ions. Received: 4 August 1997/Revised version: 28 October 1997     

An all-diode-laser-based, dual-cavity AgGaS2 cw difference-frequency source for the 9–11 μm range

2 ) nonlinear crystal is reported. The device uses a standing-wave dual-resonator scheme to enhance both near-infrared lasers. For 7 mW of 778.2-nm and 275 mW of 842.5-nm input powers, 40 nW of 10.2-μm radiation is generated by a preliminary setup. A μW-level range output power is expected after optimization of the device optical components. This compact tunable source will allow Fabry–Pérot high-resolution Doppler-free spectroscopy of spherical molecules, such as OsO₄ or SF₆, in the 9–11 μm range as an alternative source to frequency-stabilized CO₂ lasers. Received: 17 March 1998     

Anti-ferromagnetic ordering and crystal electric field in Ce:GSAG and Ce:LLGG garnets

The magnetic susceptibility of Ce:Gd₃Sc₃Al₃O₁₂ (Ce:GSAG) and Ce:La₃Lu₂Ga₃O₁₂ (Ce:LLGG) has been studied in the temperature range from 15 to 293 K. Both the Ce-doped garnets Ce:GSAG and Ce:LLGG show anti-ferromagnetic ordering at 18 and 27 K, respectively. Crystal electric field split energy levels have been used to calculate the magnetic susceptibility following Van Vleck's model. The calculated susceptibility values reasonably agree with the experimental susceptibility data of Ce:LLGG but differ for that of Ce:GSAG system. Contribution from long-range ordering between Ce and Gd ions for anomaly in Ce:GSAG system is speculated.     

A rubidium-stabilized ring-cavity resonator for optical frequency metrology: precise measurement of the D1 line in 133Cs

We have developed a ring-cavity resonator that can be used to measure the absolute frequencies of optical transitions with an uncertainty below 40 kHz. The length of the resonator is calibrated against a reference laser locked to the D₂ line of ⁸⁷Rb, the frequency of which is known with 6 kHz accuracy. We demonstrate the power of this technique by measuring the absolute frequencies of various hyperfine transitions in the D₁ line of ¹³³Cs. Our results agree with earlier measurements using the frequency-comb technique, and have similar accuracy. Measurement of the D₁-line frequency could lead to a more precise determination of the fine-structure constant. We also report a precise value of A=291.918(8) MHz for the hyperfine constant in the 6P_1/2 state.     

Effect of ionization-recombination process on fluorescent and laser properties of complex organic molecules in buffer gases

It is shown that the stepwise ionization of active organic molecules under UV pump radiation is responsible in a large part for poor lasing properties of dye-vapour active media as compared with liquid ones.