Takao Muramoto

Observation of multiple optical hole burning in ruby

Abstract Direct observation of optical hole burning in ruby is made by using a Stark-field sweeping technique. In addition to the main hole at the laser frequency, new side holes at the shifted frequencies are observed. The origin of the side holes is considered to be due to the population redistribution of resonant ions in the ground state 4 A 2 by spin-spin cross relaxation and that in the excited state Ē( 2 E) by spin-lattice relaxation. Differences from the observation by Szabo and the applicability to high resolution spectroscopy are discussed.

Sharp resonant trapping of fluorescent light R1 in ruby

Abstract Sharp decreases of R 1 in ruby are observed as a function of applied magnetic field between 4.2°K and 77°K, which can be ascribed to the resonant trapping in a localized region. Thermal broadening of E ( 2 E) is also studied below 77°K.

Coherent transients observed by Stark switching in ruby having narrow optical hole burning

Abstract By using the Stark switching technique we observed new coherent transient signals in ruby at low laser intensities, which are unique in solids where T 1 ⪢ T 2 . It was confirmed that the existence of narrow optical hole burning before the switching plays an essential role in giving rise to the signals. The effects of the multiple optical hole burning were also observed in the time domain. Assuming the existence of the holes, the signals can well be interpreted by linear system analysis.

Optical nutation echoes in ruby.

We observed the optical nutation echoes, i.e., the optical analog of rotary-spin echoes, in ruby. The experiment was carried out using a Stark switching technique. The inversion of the effective field in the rotating frame was achieved by applying a small short Stark pulse (phase-shifting pulse) whose amplitude ΔE and width Δt satisfy the condition that ΔωΔt is equal to an odd multiple of π where Δω is the frequency offset produced by ΔE. A train of nutation echoes was also observed by applying successive phase-shifting pulses. The observed nutation-echo-envelope decay time was 12 µs which is nearly equal to 2T2 consistent with the theoretical prediction. Radiation-locking and radiation-locked echo experiments were also performed by using similar phase-shifting techniques.

Stimulated Photon Echo Modulation in Ruby

A stimulated photon echo modulation varying in T (separation between the second and third pulses) due to the superhyperfine interaction between a Cr ion and neighboring Al nuclei has been observed in ruby by using a Stark switching technique. The modulation was observed for a time much longer than T2, and much higher resolution was obtained than by two-pulse photon echo experiments. An apparent disagreement between theoretical and experimental modulation patterns was noticed in the region where T>T2.

Observation of Various Photon Echoes and FID in Ruby by Stark Switching Technique

Two-pulse photon echoes, stimulated photon echoes, radiation-locked photon echoes and optical free induction decay (FID) were observed in ruby by using Stark Switching technique and their characteristics were examined. Modulation of FID was found in the off-axis case.

Absence of spectral diffusion in a dilute ruby

Abstract Spectral diffusion in a dilute (0.0034 wt%) ruby in high magnetic fields (∥ c axis) was examined by monitoring the time evolution of a narrow optical hole (width ≈0.8 MHz). It was found that the spectral diffusion due to spin flips of the neighboring Al nuclei is absent or these nuclei form a frozen core.

EPR in Optically Excited State \barE(2E) of Cr3+; Al2O3 in the Case of H⊥c3

EPR in \bar E ( 2 E ) of Cr 3+ in Al 2 O 3 for H ⊥ c 3 (θ=90°) is investigated by an optical detection and | g ⊥ | is precisely determined to be 0.0515±0.0001, which agrees fairly well with the calculated value of 0.061. The signal intensity as well as the line width varies in complicated manners depending on θ near 90°. Mechanisms of the optical detection are discussed and it is shown that the observed signals at θ=90° can be attributed to the spins whose c 3 -axes are misaligned by random strains. The θ dependence of EPR signals is also explained by assuming the presence of misaligned spins. A pair of dips was observed in the EPR line and is interpreted as the results of the cross relaxation due to one spin flip in \bar E ( 2 E ) accompanied by the flip of two spins in 4 A 2 .

Cross relaxations in ruby detected by optical method

Abstract Various cross relaxation signals in ruby are observed by monitoring the fluorescent light intensity versus magnetic field. Those between E (2E) and 4A2 are investigated in some detail. Signals due to level crossing and exchange coupled ion pairs are also observed.

Sharp Changes of Fluorescent Light in Ruby as a Function of Applied Magnetic Field

A large number of small but sharp changes (increases and decreases) of the R 1 fluorescence in ruby are observed as a function of applied magnetic field between 2 K and 77 K. At liquid helium temperatures, these signals have linewidths much narrower than the inhomogeneous linewidth (∼0.1 cm -1 ) of the R 1 line. All of these signals appear at the fields where the Zeeman splittings in the excited state \bar E ( 2 E ) and the ground state 4 A 2 satisfy an energy-matching condition for simultaneous transitions of two or more ions. Two distinct mechanisms are found to be responsible for the signals: spin-spin cross-relaxation between \bar E ( 2 E ) and 4 A 2 , and resonant self-trapping of the R 1 line. From the temperature dependence of the linewidths of the signals, thermal broadening of \bar E ( 2 E ) is measured below 77 K. Similar signals are observed in the N lines due to energy transfer from isolated ions to pairs.