Dennis Lo

VUV spectroscopy of KYF4 crystals doped with Nd3+, Er3+ and Tm3+

Abstract Emission, excitation and absorption spectra as well as luminescence decay kinetics of KYF 4 crystals doped with Nd 3+ , Er 3+ and Tm 3+ were studied in the VUV spectral range. It is shown that all the crystals have intense VUV luminescence due to interconfiguration transitions originating from the 5d states of the rare earth (RE) ions and terminating on the 4f states. The UV luminescence caused by intraconfiguration 4f–4f transitions in the RE ions is also observed from the crystals doped with the Nd 3+ or the Er 3+ ions under 4f–5d excitation. The spin-allowed 5d–4f luminescence from the crystals doped with Er 3+ or Tm 3+ is extremely weak, i.e. there exists very efficient nonradiative relaxation from higher lying 5d states to the lowest 5d level responsible for spin-forbidden luminescence. This peculiarity of the studied crystals doped with Er 3+ or Tm 3+ is very attractive for developing VUV solid-state lasers based on the crystals of such a type.

Sol–gel glass distributed feedback waveguide laser

Titania–silica glass films doped with Rhodamine 6G dye were fabricated using the low-temperature sol–gel technique. Films of thickness varying from 0.7 to 1.1 μm and of refractive index from 1.61 to 1.54 were obtained by controlling the revolution speed of spin coating and by changing the ratio of the sol–gel precursors. Tunable laser action was observed for the sol–gel glass films on glass or quartz substrates when a dynamic gain modulation was optically generated. Lasing with multiple guiding modes was achieved at a film thickness of 1.1 μm. The effect of optical confinement was studied by varying the difference of refractive indices between the sol–gel film and the substrate.

Narrow linewidth operation of solid state dye laser based on sol–gel silica

Abstract Narrow linewidth laser action was achieved in dye-doped sol–gel derived silica slabs. Using a double grating resonator cavity, one grating serving as the beam expander and the other for tuning, laser output with linewidth as narrow as 3.3 GHz was realized for dye-doped sol–gel silica slabs. The output wavelengths were 560 nm, 474 nm and 378 nm respectively for rhodamine 6G-, Coumarin 460-, Exalite 377-doped samples. Oscillatory laser waveform indicative of two or three longitudinal mode lasing was also observed.

Time-resolved spectroscopic study of phosphorescence and delayed fluorescence of dyes in silica-gel glasses

Abstract Time-resolved spectroscopy was performed to study the lowest triplet state lifetimes of erythrosin B, eosin Y and fluorescein trapped in silica-gel glasses. Room temperature phosphorescence (RTP) and delayed fluorescence (DF) were observed for erythrosin B and eosin Y. Only delayed fluorescence was observed for fluorescein. The decay lifetimes of RTP and DF were measured. The singlet–triplet intersystem crossing rate was determined. For comparison, spectroscopic measurements were also made of erythrosin B, eosin Y in gelatin, and fluorescein in boric acid. The intensity dependence of singlet–singlet absorption of organic dye molecules in sol-gel silica was studied.

Distributed-feedback dye-doped solgel silica lasers.

Dye-doped solgel silica lasers with distributed feedback were demonstrated. Solgel silica slabs doped with Rhodamine 6G or Coumarin 460 dyes were fabricated. Periodic gain modulation in dye-doped solgel silica slabs were created by the interference pattern of the pumped laser beams diffracted by a holographic grating. Laser pulse trains with subnanosecond spikes were induced. Laser emission wavelengths were centered at 480 and 585 nm for Rhodamine 6G and Coumarin 460, respectively. It was possible for us to tune approximately 20 nm around the emission centers by varying the intersection angle. The laser linewidth was of the order of 60 pm.

Zirconia and zirconia-organically modified silicate distributed feedback waveguide lasers tunable in the visible

Zirconia and zirconia-organically modified silicate waveguides of refractive index from 1.56 to 1.64 and thickness from 0.6 to 1.4 μm were prepared by the sol-gel method. Narrow linewidth (<0.5 nm) lasing was observed in dye-doped zirconia and zirconia-organically modified silicates waveguides. Tuning of the output wavelength was achieved by varying the period of the gain modulation generated by a nanosecond Nd:yttritium–aluminum–garnet laser at 532 nm. Tuning ranges were 586–618 nm and 629–657 nm for rhodamine 6G and rhodamine B, respectively. The threshold pump energy was about 50 μJ for rhodamine 6G-doped zirconia film on glass substrates.

Sol-gel silica laser tunable in the blue

Doped and undoped silica slabs were fabricated through the use of the sol-gel technique. Extended UV transmission was observed for HCl-catalyzed sol-gel silica. Under transverse pumping with a XeCl laser, narrow-linewidth (<0.9-nm) laser oscillation from silica slabs doped with coumarin 460 (C460) was achieved in a grating-resonator cavity configured in the grazing-indicence geometry. Tuning of the C460-doped silica laser extended from 468 to 494 nm. The conversion efficiency of the narrow-linewidth blue laser was 5.5%.

Spectroscopic properties of Pr3+ luminescence in complex fluoride crystals

Abstract Spectroscopic properties of several complex fluoride crystals K 2 YF 5 , KYF 4 , LiKYF 5 , CsY 2 F 7 and CsGd 2 F 7 doped with Pr 3+ have been studied under synchrotron radiation and F 2 excimer laser excitation. The Pr 3+ doped K 2 YF 5 and LiKYF 5 crystals with only a single crystallographic site for Pr 3+ ions show typical properties as in the case of spectroscopic systems where the low edge of the 4f5d Pr 3+ configuration lies slightly below the 1 S 0 level of the 4f 2 Pr 3+ configuration. The Pr 3+ :KYF 4 crystal has the same properties caused with only the 5d–4f luminescence of Pr 3+ in spite of the fact that in this crystal there are six sites suitable for Pr 3+ ions. The luminescence spectrum of the Pr 3+ :CsY 2 F 7 crystal is determined by both the 5d–4f luminescence and the 4f–4f emission originating from the 1 S 0 Pr 3+ level, which is due to two groups of optical Pr 3+ centers with the energy levels of the 1 S 0 state just between the lowest 5d levels of Pr 3+ for these two kinds of centers.

Output performance of a dye‐doped sol‐gel silica laser in the near UV

Visibly transparent near‐UV dye (Exalite 377E)‐doped silica in the form of parallelepiped were prepared by the low‐temperature sol‐gel process. The laser output performance of dye‐doped sol‐gel silica samples pumped by a short pulse (1 ns) N2 laser at 337 nm was reported. With a grating as the wavelength selection element, the laser was tuned from 367 to 387 nm with a laser linewidth of 2 nm. Using a resonator cavity consisting of two flat mirrors, the sol‐gel laser showed a slope efficiency of 34.7% and a pump energy threshold of 20 μJ. The variation of sol‐gel laser energy output as a function of the number of pulses under repetitive N2 laser excitation was investigated. The laser output energy decreased initially with the number of shots. The output energy recovered to its original intensity after a ten minute interruption in pumping. In this way, the dye‐doped samples showed no signs of long term degradation after being irradiated at 337 nm for tens of thousand shots.

Simultaneous generation of multiple pairs of transverse electric and transverse magnetic output modes from titania zirconia organically modified silicate distributed feedback waveguide lasers

Output polarization and output wavelength of titania zirconia organically modified silicate distributed feedback waveguide lasers were found to be dependent on the polarization of the crossing pump beams. Output waves with transverse electric polarization were obtained when the pump beams were s-polarized. Transverse electric and transverse magnetic optical waves belonging to the same propagation mode were generated by crossing two circularly polarized or p-polarized pump beams. Tuning of the polarized laser output was also achieved by varying the crossing angle. Up to sixteen output wavelengths corresponding to eight pairs of polarized output from eight propagation modes were observed simultaneously for a planar waveguide with a thickness of 6.7 μm.