The absorption and emission properties of transition metal (TM)-doped zinc chalcogenides have been investigated to understand their potential application as room-temperature, midinfrared tunable laser media. Crystals of ZnS, ZnSe, and ZnTe, individually doped with Cr2+, CO'+, Ni2+, or Fe,'+ have been evaluated. The absorption and emission properties are presented and discussed in terms of the energy levels from which they arise.The absorption spectra of the crystals studied exhibit strong bands between 1.4 and 2.0 pm which overlap with the output of strained-layer InGaAs diodes. The room-temperature emission spectra reveal wide-band emissions from 2-3 pm for Cr and from 2.8-4.0 pm for Co. Cr luminesces strongly at room temperature; CO exhibits significant losses from nonradiative decay at temperatures above 200 K, and Ni and Fe only luminesce at low temperatures. Cr2+ is estimated to have the highest quantum yield at room temperature among the media investigated with values of -75-100%.Laser demonstrations of Cr:ZnS and Cr:ZnSe have been performed in a laser-pumped laser cavity with a Co:MgFL pump laser. The output of both lasers were determined to peak at wavelengths near 2.35 pm, and both lasers demonstrated a maximum slope efficiency of approximately 20%. Based on these initial results, the CrL+ ion is predicted to be a highly favorable laser ion for the mid-IR when doped into the zinc chalogenides; CO'+ may also serve usefully, but laser demonstrations yet remain to be performed.

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Low detection sensitivity stemming from the weak polarization of nuclear spins is a primary limitation of magnetic resonance spectroscopy and imaging. Methods have been developed to enhance nuclear spin polarization but they typically require high magnetic fields, cryogenic temperatures or sample transfer between magnets. Here we report bulk, room-temperature hyperpolarization of 13C nuclear spins observed via high-field magnetic resonance. The technique harnesses the high optically induced spin polarization of diamond nitrogen vacancy centres at room temperature in combination with dynamic nuclear polarization. We observe bulk nuclear spin polarization of 6%, an enhancement of ∼170,000 over thermal equilibrium. The signal of the hyperpolarized spins was detected in situ with a standard nuclear magnetic resonance probe without the need for sample shuttling or precise crystal orientation. Hyperpolarization via optical pumping/dynamic nuclear polarization should function at arbitrary magnetic fields enabling orders of magnitude sensitivity enhancement for nuclear magnetic resonance of solids and liquids under ambient conditions.

We have used IR excitation to selectively create populations in admixtures of the zeroth-order states comprising the ∼3000 cm−1 ‘‘C–H stretching Fermi triad’’ of benzene. UV spectra of the 260 nm Ã(1B2u)←X̃(1A1g) transition in the IR-excited molecules show several new bands, which we have assigned. Final states in the UV transitions are some vibrational levels which have not been detected before, allowing us to find several excited-state vibrational frequencies. We have determined ν′3 =1327±3 cm−1, ν19 =1405±3 cm−1, and ν′20 =3084±5 cm−1. Also, vibrational structure which was unresolved in IR spectra of the ‘‘Fermi triad’’ was resolved in the UV double resonance spectra, confirming that the C–H stretching admixture is really a tetrad. The 3048, 3079, and 3101 cm−1 states had formerly been given the labels ν″20, ν″8+ν″19, and ν″1+ν″6+ν″19, respectively. Actually, the middle level most nearly resembles ν″1+ν″6+ν″19, and the 3101 cm−1 level is strongly mixed with ν″3+ν″6+ν″15. As predicted by molecular orbital theory, excited-state C–H bending and stretching frequencies are not very different from those in the ground state. Furthermore, we suggest that the four C–H stretching frequencies increase uniformly by ∼20 cm−1 in the excited state; reexamination of the Atkinson and Parmenter 260 nm Ã←X̃ spectrum leads us to reassign ν2 from 3130 to ∼3093 cm−1, which is 19 cm−1 above ν″2. There is a Fermi resonance between the ν6+ν′20 level and another level ∼13 cm−1 lower in energy; the strength of the perturbation is ∼18 cm−1. Possibilities for the perturbing vibrational state are ν6+ν′8+ν14 and ν′6+ν13.

Lasing of Fe:ZnSe is demonstrated, for the first time to the authors' knowledge, for temperatures ranging from 15 to 180 K. The output wavelength of the Fe:ZnSe laser was observed to tune with temperature from 3.98mum at 15 K to 4.54mum at 180 K. With an Er:YAG laser operating at 2.698mum as the pump source, a maximum energy per pulse of 12muJ at 130 K was produced. Laser slope efficiencies of 3.2% at 19 K and 8.2% at 150 K were determined for an output coupling of 0.6%. A laser emission linewidth of 0.007mum at 3.98mum was measured at 15 K. Absorption and emission spectra and emission lifetimes for Fe:ZnSe are also discussed.

We used rotational cooling of molecules to -5°K by supersonic expansion and state-selective, multilevel saturation spectroscopy to obtain high-resolution spectra of the fundamental and first and second overtone transitions of C-H stretching modes in benzene and its dimer.Greatly reduced linewidths (<3 cm FWHM) in the rich spectra show that previously reported spectra have suffered from inhomogeneous congestion. Our observed spectral widths indicate that the vibrational lifetimes of the C-H stretches are at least a few psec, even at the energy of the second overtone (8800 cm 1 .) The "local mode" picture appears to apply when at least 3 quanta of C-H stretching motion are present. Spectra of the dimer are similar to those of the monomer but show a red shift of a few cm 1 , the appearance of combination bands involving van der Waals vibrational modes, some intensity changes, and a broadening of spectral features that increases with the vibrational energy. The dimer's predissociation lifetime at -3000 cm 1 vibrational energy exceeds -3 psec.

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