Ions In Ruby Research Articles

On the Thermal Spectra of Ruby and Sapphire

The temperature dependence of the thermal spectra (in the range from 0.4 to 8 μm) of ruby and sapphire single crystals heated by a 10.6-μm cw electric-discharge CO2 laser has been experimentally and analytically investigated. The shape of the background of the spectral lines of impurity Cr3+ ions in ruby corresponds to the short-wavelength tail of sapphire thermal radiation. The Planck thermal spectrum of sapphire is interpreted in terms of the interaction between electrons and lattice ions in the conduction band.

Observing electron spin resonance between 0.1 and 67 GHz at temperatures between 50 mK and 300 K using broadband metallic coplanar waveguides

We describe a fully broadband approach for electron spin resonance (ESR) experiments, where it is possible to tune not only the magnetic field but also the frequency continuously over wide ranges. Here, a metallic coplanar transmission line acts as compact and versatile microwave probe that can easily be implemented in different cryogenic setups. We perform ESR measurements at frequencies between 0.1 and 67 GHz and at temperatures between 50 mK and room temperature. Three different types of samples (Cr3+ ions in ruby, organic radicals of the nitronyl-nitroxide family, and the doped semiconductor Si:P) represent different possible fields of application for the technique. We demonstrate that an extremely large phase space in temperature, magnetic field, and frequency for ESR measurements, substantially exceeding the range of conventional ESR setups, is accessible with metallic coplanar lines.

Strong coupling between whispering gallery modes and chromium ions in ruby

We report the study of interactions between cavity photons and paramagnetic Cr$^{3+}$ spins in a ruby (Cr$^{3+}$:Al$_2$O$_3$) Whispering Gallery mode (WGM) resonator. Examining the system at microwave frequencies and millikelvin temperatures, spin-photon couplings up to 610 MHz or about 5% of photon energy are observed between the impurity spins and high quality factor ($Q > 10^5$) WGM. Large tunability and spin-spin interaction allows operation in the strong coupling regime. The system exhibits behaviour not predicted by the usual Tavis-Cummings model because of interactions within the two-level spin bath, and the existence of numerous photonic modes.

Fracto-mechanoluminescence from ruby and Cr doped spinel in cutting, grinding and polishing processes

Red colored bright visible light fracto-mechanoluminescence was observed successfully from ruby (Cr doped Al2O3) and Cr doped spinel (Cr doped MgAl2O4) crystals in mechanical processes such as cutting, grinding and polishing. Fracto-mechanoluminescence spectra from ruby (peaking at λ=696nm) and Cr doped spinel (peaking at λ=693nm) perfectly agree with those of photoluminescence (PL) from Cr3+ ions in ruby and spinel crystals, respectively. In the grinding and polishing processes, peak intensities and peak wavelength of fract-mechanoluminescence from ruby and Cr doped spinel crystals varies with roughness (grain size, #) of the diamond disk. Fracto-mechanoluminescence is expected to be used in the in-situ evaluation of fracture of crystals in cutting, grinding and polishing for highly precise mechanical processes.

Baryscan: a sensitive and user-friendly alternative to Z scan for weak nonlinearities measurements

A new and efficient technique for measuring weak optical nonlinearities is reported. Like Z scan, its implementation is basic, both experimentally and theoretically, but leads to an improved sensitivity of λ/5.10⁴, which represents, to date, one of the highest observed enhancements. With this technique, which is based upon the use of a position sensitive detector, nonlinear properties are deduced by monitoring the barycentric position of a truncated pump-probe laser beam as the sample is moved along the optical axis. The technique is experimentally validated by measuring the pump-induced refractive index change and the underlying polarizability variation resulting from the excitation of the Cr(3+) ions in ruby.

Coherent population trapping in a crystalline solid at room temperature

Observation of coherent population trapping (CPT) at ground-state Zeeman sublevels of $Cr^{3+}$-ion in ruby is reported. The experiments are performed at room temperature by using both nanosecond optical pulses and nanosecond trains of ultrashort pulses. In both cases sharp drops in the resonantly induced fluorescence are detected as the external magnetic field is varied. Theoretical analysis of CPT in a transient regime due to pulsed action of optical pulses is presented.

Trapping of point-contact-generated 29-cm-1 phonons in ruby.

Trapping of 29-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ phonons by optically excited ${\mathrm{Cr}}^{3+}$ ions in ruby is studied at phonon occupations of up to order unity. The 29-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ phonons are supplied by transient excitation of a metallic point contact and subsequent conversion of the injected phonons to resonance. The growth and the decay of the trapped phonon population are markedly non-single-exponential quantities, particularly at higher phonon populations. A quantitative analysis of these effects is made on the basis of phenomenological rate equations of the ion and phonon populations. These equations make explicit allowance for the line shape of the E\ifmmode\bar\else\textasciimacron\fi{}${(}^{2}$E)-2A\ifmmode\bar\else\textasciimacron\fi{}${(}^{2}$E) phonon transition as well as for feeding and loss of resonant phonons by mediation of weakly exchange-coupled ${\mathrm{Cr}}^{3+}$ pairs. At the higher phonon occupations, the transition appears to be dynamically broadened by stimulated phonon emission, which reduces the trapping efficiency.

The Effect of Spin—Orbit Interaction on the Intensity of Transitions from 4A2 and 2E States in Strong Crystal Fields

AbstractThe effect is studied of spin—orbit interaction and low‐symmetry field on the absorption ratios of the wide bands of the excited‐state absorption spectrum and similar bands of the ground‐state absorption spectrum of d3‐configuration. The study includes calculations of the energy of the pure electron transitions and the analysis of the composition of the eigenfunctions of the Cr3+ ions in ruby, magnesium oxide, and emerald in the cubic field approximation and taking mixing of all terms of the double trigonal group into account. The results are compared to the experimental values of the ratios of the oscillator strengths of the transitions compared. It is shown that the ratios depend strongly enough on the crystal field parameters and the parameter of the spin—orbit interaction. The influence of the interaction under consideration on the lasing parameters is discussed.

Picosecond excite-and-probe absorption measurement of the 4T2 state nonradiative lifetime in ruby

In a picosecond excite-and-probe absorption measurement, a 527-nm picosecond pulse excites the 4T2 state of the Cr3+ ion in ruby and a 3.4-μm picosecond probe pulse monitors the growth and decay of population in the 2E state as a function of pump-probe delay. From the growth of population in the metastable 2E state, an upper limit of 7 ps for the nonradiative lifetime of the 4T2 state is determined.

Similarity of Ground‐ and Excited‐State Absorption Spectra of Cr3+ Ions in a Strong Crystal Field

AbstractA comparative analysis of the broad bands of the ground‐ and excited‐state absorption spectra of d3‐impurity ions iscarried out in a point‐ion crystal field theory model. It is found that for d3 electrons in the cubic field (d7 in tetrahedral field) a similarity of these bands should be expected. The similarity results from the particular symmetry of the initial terms of the compared transitions (these terms correspond to the t32 half‐filled shell of the strong cubic field) and from the same orbital symmetry ofthe final state wave functions. Theoretical conclusions are applied to the experimental spectra of Cr3+ ions in ruby, emerald, and MgO. The use of the similarity of ground‐ and excited‐absorption spectra is suggested. The same analysis is carried out for the d2 configuration as well.

Homogeneously broadened far-infrared absorption line due to the [formula omitted] transition of excited chromium ions in ruby

By use of far-infrared laser spectroscopy, we have found that for a high-quality ruby crystal at low temperature, the absorption line due to the electronic transition between the excited states E( 2E) and 2 A( 2E) of Cr 3+ ions is homogeneously broadened. From the linewidth (0.011 cm -1) the lifetime of the 2Ā level against emission of 29 cm -1 phonons is obtained.

Temperature dependence of the Ē → 2Ā far-infrared absorption line of excited chromium ions in ruby

By using far-infrared laser spectroscopy we have studied the temperature dependence of the absorption that is due to transitions between the E ((2)E) and 2A ((2)E) levels of excited Cr(3+) ions in ruby. From the temperature dependence of the linewidth we determined the inhomogeneous and the homogeneous contributions to line broadening. From the homogeneous width the lifetime of the 2A level was obtained. We found that, for emperatures up to 70 K, the lifetime is due mainly to one-phonon relaxation, whereas at higher temperatures another relaxation process, probably a two-phonon Raman process, becomes strong.

Electric field-induced double-quantum transitions in paramagnetic systems

The interaction of an intense microwave electric field with Cr3+ ions in ruby is investigated. The authors report solutions for the electric and magnetic polarisation vectors oscillating at the second-harmonic frequency of the driving field and a comparison with experimental data.

Cross-relaxation to (3d)1ions in ruby

Resonant cross-relaxation (RCR) and non-resonant cross-relaxation (NCR) measurements are reported on ruby crystals containing Ti3+ as an additional impurity, RCR is shown to be dominated by the Ti3+-lattice process. The temperature dependences of RCR and NCR both give values for the splitting between the ground and first excited Kramers doublets of Ti3+ which are less than that expected but possible reasons are put forward, RCR is also reported in ruby crystals containing V4+ and the results are explained in terms of NCR involving V3+ ions. It is concluded that the ion-lattice coupling is larger for V4+ than for Ti3+ but both are smaller than that for V3+. A table is given which lists all NCR and RCR measurements which have been carried out on all (3d)n ion impurities in ruby.

High magnetic field spin-lattice relaxation rates in the ground state of A Cr 3+ ion in ruby

Employing pulsed magnetic fields with rectangular shapes, we observed by optical measurements the spin-lattice relaxation rates in the 4A 2 state of Cr 3+ ions in ruby. Relaxation rates are found to be proportional to squares of magnetic fields in the range 4.7 to 12.8 T at 4.2 K.

Theory of the pressure dependence of a prototype exchange integral

The variation of electron exchange integrals in solids subjected to hydrostatic pressures $P$ is considered by examining a prototype exchange integral $J$. The quantity $(\frac{1}{J})(\frac{\mathrm{dJ}}{\mathrm{dP}})$ is determined within the context of a theory of solids under hydrostatic pressures in which the application of pressure is represented in terms of the crystal compressibility and two parameters which are associated with electronic screening and wavefunction-distortion effects. Pressure variations of magnetic-phase boundaries, exchange-enhanced susceptibilities, and exchange interactions of pairs of ${\mathrm{Cr}}^{3+}$ ions in ruby are considered as examples of the applications of the results.

High Magnetic Field Spin-Lattice Relaxation Rates in the Ground Quartet State of a Cr3+ Ion in Ruby

Relaxation-rates in 4 A 2 state of a Cr 3+ ion in ruby have been studied by optical observation on population changes caused by application of magnetic field of rectangular pulses at 4.2 K. The direct one phonon emitting process is dominant in the field range from 47 kOe to 128 kOe. No transition occurs between the levels \(M_{S}{=}\frac{1}{2}\) and \({-}\frac{1}{2}\), where M S is the component of spin angular momentum along the field. The two types of transitions, Δ M S =2 and Δ M S =1, are found to constitute the spin-lattice relaxation. The rates of these transitions are (7.66±0.15)×10 -4 H 2 ms -1 , and (7.65±0.20)×10 -5 H 2 ms -1 , resrectively, where H is the magnetic field strength in kOe.

The effect of optical unloading of a passive shutter on the energy parameters of a single-pulse ruby laser

The present paper presents the results of an experimental investigation of the effect of the shutter unloading coefficient on the energy parameters of a ruby laser. The unloading coefficient is understood to mean the ratio between the radiation densities on the shutter surfaces facing one another and the end surface of the active element. The measurements were carried out for two types of shutters: a shutter made of KS-19 glass and a shutter based on a solution of kryptocyanin in ethanol. The chosen shutters have substantially different spectroscopic parameters. The duration ~- of the excited state for KS-19 glass is 10 -? sec [3 ], while for kryptocyanin it is T ~ 10 -10 sec. The absorption cross section a s at the ruby lasing wavelength is estimated to be ~ 6 �9 10 -19 [3] and 4.10 -16 cm 2 respectively. The majority of other known media for passive shutters haveparameterswh ich fall in the interval between the indicated values. Since ~s is much greater than the absorption cross section of ions in ruby (ar = 2.5.10 -20 cm2), it follows that for Unloading of the shutter one-pulse lasing may be observed within certain limits [4]. The relative optical unloading of the shutter was accomplished by means of a telescopic system. The scattering component of the telescope was a concave spherical surface (R l = 127.6 mm) implemented using the end-face of the active element. A rod having a diameter of 10 mm and a length of the active portion equal to 120 mm was used; its surface was of the matte type. An iris 5 mm in diameter which isolated the uniformly pumped region of the ruby was mounted flush against the spherical surface. The second component of the telescopic system consisted of changeable plane-concave lenses made of K-8 glass which were mounted in optical contact with the shutter made of KS-19 glass or with the window of the vessel if a solution of kryptocyanin was used as the shutter. The lenses used had focal distances of 254, 354, 516, and 685 mm. The resonator was formed by a stack of two glass plates and a dielectric mirror having a reflection coefficient close to unity. The initial transmission of both types of shutter was chosen to be identical and equal to 0.25. The distance between the telescope components at which the lasing energy was maximal was selected for each removable lens, and the duration of the lasing was determined in this portion of the telescopic system. The values of the unloading coefficient of the shutter were 2.5, 5, 10, and 20 in the tests. The pumping was identical and equal to 600 J in all cases.

Calculation of Absorption Intensities of Cr3+Ion Pair Lines in Ruby

Abstract The calculation of relative intensities of the optical absorption lines of the fourth order pair of Cr3+ ions in ruby has been performed assuming the electro-dipole character of the transitions.

Cr3+ Ion Pair Spectrum in Ruby

The optical spectrum due to the exchange coupled Cr 3+ ions in ruby has been studied theoretically. The effect of the lowering of the Cr 3+ site symmetry due to the formation of a pair was taken into account. For the 2nd neighbor pair, a good fitting of the excited state energies between theory and experiment was obtained. The effect of the higher order exchange is found to be very important for this pair. It is also found that the deviation of the Cr 3+ site symmetry from C 3 is rather large for this pair. For the 4th neighbor pair, the level diagram of the excited state was obtained and the absorption intensities were calculated. Most of the observed lines in this pair are explained by this theory. The lines so called N 1 and N 2 are found to be the transitions due to the exchange induced electric dipole.