J.P.D. Martin

Site selective excitation, upconversion and laser operation in Er3+:LiKYF5

Abstract The energy level structures of Er 3+ ions occupying two, almost identical, low symmetry Y 3+ sites in LiKYF 5 have been determined using site selective laser excitation and luminescence. The positions of the (2 J +1)/2 Stark levels of 10 of the lowest energy multiplets were obtained. Upconversion fluorescence in the green, blue and violet while exciting the 4 I 15/2 → 4 F 9/2 transition was observed and modelled via excited state absorption and energy transfer processes populating the energy levels of the 4 S 3/2 , 2 H 9/2 and 2 P 3/2 multiplets. Room temperature upconversion laser operation in the green at 550 nm has also been achieved by pumping the 1% Er 3+ :LiKYF 5 gain medium with laser diodes at 651 and 800 nm.

Laser spectroscopy and hole burning of europium laurate and europium-doped lanthanum laurate

Abstract Laser spectroscopy and hole-burning measurements have been made on samples of europium laurate and europium-doped lanthanum laurate. The lanthanide laurate soaps are lanthanide salts of long chain (C 12 ), saturated fatty acids in which 2D layers of hydrocarbon chains arise, forming either lamellar crystals or smetic liquid crystals depending on their thermal history. In this study, solid samples of metastable liquid crystals were prepared by different cooling rates which resulted in a variation of the local disorder about the europium ions. Two symmetrically distinct europium sites have been identified within slowly cooled europium laurate.

Spectral hole burning and Raman heterodyne signals associated with an avoided crossing in the NV centre in diamond

Abstract The nitrogen-vacancy centre in diamond exhibits an avoided crossing of ground state electron spin levels in a magnetic field of ∼1028 G applied along the 〈1 1 1〉 direction. In this paper, the magnetic field dependence of Raman heterodyne signals and the optical transmission at 638 nm in the vicinity of the avoided crossing are reported. It is discussed that the optically induced spin polarization of ground state populations produces anomalous fine structure hole-burning behaviour.

Hyperfine coupling between crystal-field levels in the tetragonal centre of CaF2:Ho3+

Presents and discusses the high-resolution optical spectrum associated with 5I8(A1) implies 5F5(E), 5I8(A2) implies 5F5(E) transitions of a tetragonal Ho3+ centre in CaF2. The lowest crystal-field levels in the ground multiplet are two singlets separated by approximately 1.7 cm-1. With the closeness of the states, the hyperfine interaction gives rise to strongly mixed wavefunctions and anomalously large pseudoquadrupole splittings. The mixing also results in an enhanced magnetic moment associated with the hyperfine components of the singlets and the magnitude is found to depend on the hyperfine level. Consequently, there are separate superhyperfine resonances associated with each of the four non-degenerate hyperfine levels and these resonances were observed by ODNMR techniques when holeburning in the various optical hyperfine lines. More than 30 superhyperfine resonances were detected and they are assigned to interstitial and groups of near-neighbour F- ions.

Raman heterodyne detected magnetic resonance: I. CW and coherent transient measurements

We report cw and coherent transient studies on electronic and nuclear magnetic transitions of the nitrogen-vacancy centre in diamond using an optical-rf double resonance technique: Raman heterodyne detection. Emphasis is placed on the coherent transient measurements to illustrate the versatility of the detection technique, which is not only very sensitive but is also ideal in this case since it is based on a coherent process. In this paper we show that Raman heterodyne detection can be used to obtain a wide range of signals including nutation, spin echo, rotary echo and spin locking in a single system. Finally an example of using coherent transients to test the validity of the Bloch equation is given.

Probing a doubly driven two-level atom

A two-level system is driven by two strong fields, one on resonance and one close to resonance. There is a resonance-like response of the coupled atom-field system when the detuning of the second field is an integer fraction of the Rabi frequency of the resonant field. These subharmonic resonances are monitored by a transition to a third level and give a characteristic spectrum dominated by a series of doublets.

Zero-field hole burning and transient effects in LaCl3:Ho3+

Abstract Two laser spectral hole burning in the hyperfine lines of the 646.9 nm transition of 0.0018% Ho3+:LaCl3 is presented and discussed. It is shown that the hole burning in this centre can be described by a simple rate equation model where the optical pumping competes with electron-electron and nuclear-nuclear spin flips. We also illustrate using the rate equation model the temporal development of the holes and antiholes and finally present values for the ground state hyperfine and quadrupole interaction strengths, obtained from optical/microwave double resonance measurements.

Spectral hole burning in the hyperfine lines of LaCl3:Ho3+

Two laser spectral hole burning in the hyperfine split 649.9 nm ( 5 I 8 - 5 F 5 ) line of a 0.1% Ho 3+ doped LaCl 3 crystal at 2 K is presented and discussed. The process of hole burning in this centre is thought to arise from optically induced spin flips which under CW conditions complete with the relaxation processes causing electron-electron and nuclear-nuclear spin flips. In support of this mechanism, we also discuss a simple rate equation model which describes the interaction between the optical pumping and relaxation processes

Zeeman measurements of Pr3+ centres in CaO and CaF2

Abstract Three Pr 3+ centres in two different crystal hosts have been studied by site selective laser spectroscopy and Zeeman spectroscopy with attention directed at the 3 P 0 , 3 P 1 and 1 I 6 crystal field level assignments. The 3 H 4 → 3 P 0 excitation line is readily identified in each case. For a tetragonal and a trigonal centre in CaF 2 there is, in each case, a further weak excitation line higher in energy which exhibits a large Zeeman splitting. The associated excited levels are attributed to 1 I 6 states. For the Pr 3+ centre in CaO there are two lines adjacent to that associated with the 3 P 0 state and although they do not exhibit linear Zeeman splittings, there are quadratic Zeeman shifts due to large off-diagonal terms. Again the related levels are attributed to 1 I 6 states. The centre is shown to have orthorhombic symmetry and the energy levels for this centre are determined.

Raman heterodyne detected magnetic resonance: II. Magnetic transitions of NV centre at level anticrossing region

In the preceding paper [1] we reported both cw and coherent transient measurements carried out in EPR and NMR transitions within the3A ground state of the nitrogen-vacancy centre in diamond using the Raman heterodyne detection technique. In this paper we use these measurements to characterise the nuclear magnetic transitions near a level anticrossing situation. The level anticrossing causes a mixing of the electronic spin and nuclear spin wave functions which results in a greatly enhanced NMR transition moment. The amount of mixing not only affects the dipole moment but, correspondingly, the characteristic relaxation times. In this paper we report the measurement of these parameters in the nitrogen-vacancy centre as a function of applied Zeeman field strength and analyse the results using the spin Hamiltonian formalism. Furthermore, combined with the particular features of the Raman heterodyne technique, such a system represents an ideal testing ground for the nonlinear behaviour of strongly driven transitions. Some results are illustrated, including dynamic Zeeman splitting and gain without inversion.