Ground-state depleted laser in neodymium-doped yttrium orthosilicate

A ground state depleted (GSD) 1,2 laser has been demonstrated in the form of a Q-switched oscillator operating at 912 nm. Using Nd 3+ as the active ion and Y2SiO5 as the host material, the laser transition is from the lowest lying stark level of the Nd 3+4 F 3/2 level to a stark level 355 cm -1 above the lowest lying one in the 4 I 9/2 manifold. The necessity of depleting the ground 4 I 9/2 manifold is evident for this level scheme as transparency requires a 10% inversion. To achieve the high excitation levels required for the efficient operation of this laser, bleach wave pumping using an alexandrite laser at 745 nm has been employed. The existence of a large absorption feature at 810 nm also allows for the possibility of A1GaAs laser diode pumping. Using KNbO 3 , noncritical phase matching is possible at 140°C using d 32 and has been demonstrated. The results of Q-switched laser performance and harmonic generation in KNbO 3 will be presented. Orthosilicate is a monoclinic biaxial crystal. An oriented spectroscopic evaluation consisting of a Judd-Ofelt analysis of oriented absorption spectra and the measurements of oriented emission spectra has been completed and will be presented. Results of modeling using these spectroscopically determined parameters will be compared with the actual laser performance. The performance of this laser at 911 nm which allows accessing Cs atomic resonance filters through harmonic doubling will also be discussed. Orthosilicate can be grown in large boules of excellent optical quality using a Czochralski technique. Because of the relatively small 912 nm emission cross section of 2-3 x 10 -20 cm 2 (orientation dependent) fluences of 10-20 J/cm 2 must be circulated in the laser cavity for the efficient extraction of stored energy. This necessitates very aggressive laser damage thresholds. Results from the Reptile laser damage facility at Lawrence Livermore National Laboratory (LLNL) will be presented showing Y 2 SiO 5 bulk and AR sol-gel coated surface damage thresholds of greater than 40 J/cm 2 for 10 nsec, 10 Hz, 1.06 μ pulses.