Results of a Direct Search Using Synchrotron Radiation for the Low-Energy (229)Th Nuclear Isomeric Transition.

We report the results of a direct search for the (229)Th (I(π)=3/2(+)←5/2(+)) nuclear isomeric transition, performed by exposing (229)Th-doped LiSrAlF(6) crystals to tunable vacuum-ultraviolet synchrotron radiation and observing any resulting fluorescence. We also use existing nuclear physics data to establish a range of possible transition strengths for the isomeric transition. We find no evidence for the thorium nuclear transition between 7.3 eV and 8.8 eV with transition lifetime (1-2) s≲τ≲(2000-5600) s. This measurement excludes roughly half of the favored transition search area and can be used to direct future searches.

Periodically poled BaMgF(4) for ultraviolet frequency generation.

Ferroelectric domain inversion has been demonstrated in BaMgF(4) . Transparency has been measured to <140nm, and no change in transmission was measured under 157-nm irradiation for >1.1x10(9) shots at 2mJ/cm(2) per pulse. First-order quasi-phase-matched generation of 157 nm is predicted by use of grating periods as long as 1.5mum. This material should permit shorter-wavelength chi((2)) frequency-mixing processes than with any other crystalline material.

14-fs pulse generation in Kerr-lens mode-locked prismless Cr:LiSGaF and Cr:LiSAF lasers: observation of pulse self-frequency shift.

Kerr-lens mode-locked Kr-laser-pumped Cr:LiSGaF and Cr:LiSAF lasers containing only two newly developed low-loss chirped mirrors instead of conventional dielectric resonator mirrors and generating pulses of widths as small as 14-fs with as much as 100 mW of average output power are reported. We report what is to our knowledge the first experimental observation of a pulse self-frequency shift in crystalline active media that are characteristic of such short pulses at megawatt intracavity peak powers. We also believe this phenomenon to be one of the significant limiting factors for pulse duration in femtosecond Cr:LiSAF-type lasers.

Investigation of diode-pumped 2.8-microm laser performance in Er:BaY(2)F(8).

Laser operation at 2.8 microm in BaY(2)F(8) with erbium concentrations of 7.5% and 20% is investigated under laser-diode pumping at 967 nm. Output powers as high as 250 mW and slope efficiencies as high as 24% are obtained. Results are comparable with those of Er(3+):LiYF(4) under the same pump conditions. Slope efficiencies above 30% are predicted for optimized erbium concentrations.

Efficient continuous-wave TEM(00) and femtosecond Kerr-lens mode-locked Cr:LiSrGaF laser.

Efficient high-power (900-mW) TEM(00) cw operation of a Cr:LiSrGaF laser pumped by a Kr(+) laser is demonstrated. The results of laser and spectroscopic analysis, including upconversion and excited-state absorption, are presented and used for the optimization of this laser. Kr(+)-laser-pumped mode-locked femtosecond operation (64 fs) was performed. Use of a modified resonator, which can decrease the threshold pump and intracavity power for Kerr-lens mode locking and increase the mode-locked output power (300 mW), is suggested. The inf luence of crystal axis misalignment on the tuning and mode-locking characteristics of the laser is studied.

Prismless passively mode-locked femtosecond Cr:LiSGaF laser.

A Kerr-lens mode-locked Cr:LiSrGaF laser containing no intracavity prisms has been demonstrated for the first time to the authors' knowledge. The laser produced stable near-transform-limited 44-fs pulses with an output power of 200 mW, tunable between 833 and 857 nm. Low-loss Gires-Tournois structured dielectric mirrors were used for dispersion control. The measured group-delay dispersion of the active medium as well as of the mirrors permitted to minimize the number of reflections, permitting higher output power.

Kerr-lens mode-locked diode-pumped Cr:LiSGAF laser.

We have demonstrated stable and self-sustaining Kerr-lens mode locking of a Cr:LiSGAF laser pumped by AlGaInP laser diodes. A hard aperture near one end of the laser provides the necessary amplitude modulation. This allsolid- state system generates transform-limited 100-fs pulses, tunable from 810 to 860 nm. The average power at 830 nm is 35 mW, with fluctuations of much less than 1%. The thermal properties of Cr:LiSGAF will permit scaling of these results to higher power.

Self-pumped phase conjugation and four-wave mixing in 0 degrees - and 45 degrees -cut n-type BaTiO(3):Co.

Relatively fast self-pumped phase-conjugate and four-wave-mixing rise times are reported in n-type cobalt-doped barium titanate. With the crystal oriented in a 45 degrees cut as compared with the same crystal in a 0 degrees cut we find a factor of 3 decrease in the 0-90% rise time to 800 ms with 25-mW input power at 514.5 nm. Also, the self-pumped phase-conjugate reflectivity increases from 20% to 40%. We deduce that the phase conjugation is from internally seeded stimulated photorefractive backscattering. The four-wave-mixing rise time of the 45 degrees -cut crystal is 4 ms with a reflectivity of 48% when the pumping beams are derived from self-pumped phase conjugation that has an input power of 25 mW.

Tunable-laser performance in BeAl(2)O(4):Cr(3+).

Broadly tunable laser operation has been obtained at room temperature from the vibronic bands of single-crystal BeAl(2)O(4):Cr(3+) under Xe-flashlamp excitation. Continuous tuning is obtained from 701 to 794 nm, with maximum power at 750 nm. Long-pulse operation employing 6.3-mm x 76-mm rods easily provides 500 mJ in 200-microsec bursts, whereas 70-mJ, 120-nsec pulses are obtained under Q-switch operation.