Yehoshua Kalisky

Quantitative studies of Cr4+:YAG as a saturable absorber for Nd:YAG laser

Abstract The performance of a Q -switched Nd:YAG laser using Cr 4+ :YAG as a passive Q -switched is reported. The Q -switched pulse contains two orders of magnitude more energy than the free running spike. An increase in the energy extraction efficiency of the Q -switched pulse with the appearance of multiple spikes, as well as shortening of the Q -switched pulsewidth were observed and analyzed.

Some optical properties of Cr4+-doped crystals

We summarize briefly some of our past studies, and report of preliminary recent new results concerning the optical properties of Cr 4+ -doped crystals that are important for utilization as passive Q-switching devices in Nd:YAG laser systems. The host crystals involved are YAG, YSGG, GGG, LuAG and forsterite. Excited-state lifetimes of 4.0, 1.0 and 1.7 μs were measured by the Cr 4+ fluorescence decay (1.3-1.7 μm) following pulsed excitation at 1064 nm in YAG, YSGG and GGG, respectively. The ground- and excited-state absorption (ESA) cross-sections at λ = 1064 nm were estimated from transmission saturation measurements. For [Cr 4+ ,Mg 2+ ]:YAG the respective results were σ gs = (3.25 ± 0.15) × 10 -18 cm 2 and σ es = (6.25 ± 0.5) × 10 -19 cm 2 . In the orthorhombic forsterite, the cross-sections were polarization dependent. We got σ gs < (3.3 ± 1) × 10 -19 cm 2 for E∥a∥, σ gs = (23 ± 2) × 10 -19 cm 2 and σ es = (9.0 ± 0.7) × 10 -19 cm 2 for E∥b, and σ gs = (16 ± 1) × 10 -19 cm 2 and σ es = (5.7 ± 0.4) × 10 -19 cm 2 for E∥c. Polarised ESA spectra were measured between 680 and 960 nm using the pulsed pump/probe technique. At 750 nm we got σ gs = (110 ± 10) × 10 - 19 cm 2 and σ es = (25 ± 3) × 10 -19 cm 2 for E∥b. Passive Q-switching performance of a flashlamp-pumped Nd:YAG laser using an intracavity [Cr 4+ ,Ca 2+ ]:GGG sample is also demonstrated.

Impurity local phonon nonradiative quenching of Yb/sup 3+/ fluorescence in ytterbium-doped silicate glasses

We have studied the concentration quenching of Yb/sup 3+/ ion fluorescence in Yb-doped silicate glasses containing up to 3.4/spl times/10/sup 21/ cm/sup -3/ Yb/sup 3+/ ions. The absorption and fluorescence spectra are similar to those obtained for the Yb/sup 3+/ ion in many different matrices, with a radiative lifetime of approximately 1400 /spl mu/s. The fluorescence decay curves were different among samples, with strong dependence on the Yb concentration. The decay curves could always be resolved into two exponential components, indicating that the ions reside in two different sites, each of a different characteristic nonradiative decay mechanism. The fast decay times ranged between 6 and 300 /spl mu/s, and the slow ones ranged between 190 and 1250 /spl mu/s in different samples. The sites where ions exhibit the fast decay most probably consist of pairs of Yb/sup 3+/ ions. The nonradiative decay probabilities for each site mere directly proportional to the Yb/sup 3+/ concentration in the same site. We propose that the fluorescence quenching occurs by multiphonon nonradiative transitions involving polar local phonon bands created by the presence of the Yb/sup 3+/ ion.

Efficient up-conversion in KYb0.8Eu0.2(WO4)2 crystal

Abstract Efficient visible anti-Stokes emission was observed in the KEu 0.2 Yb 0.8 (WO 4 ) 2 crystal after a direct excitation of the Yb 3+ ion. This emission is associated with the Eu 3+ ion and originates not only from the 5 D 0 state but also from the 5 D 2 and 5 D 1 states. The process of up-conversion was investigated at 300 K as a function of excitation power. It was demonstrated that the process was non-linear and changed with the incident power as P exc n , n =1.5. The mechanism of up-conversion processes occurring in the KEu 0.2 Yb 0.8 (WO 4 ) 2 crystal is briefly discussed.

New trends in lasers and laser crystals

The current trends in lasers and laser crystals will be addressed. The technological challenges and global market forecast for non-diode laser sales will be presented as well. The present status of lasers, their various applications and the design considerations of a laser system will be discussed, with some future applications which can enjoy the benefit of laser crystals. As an example, we shall present and analyse a special case, where the use of a laser system provides significant advantage over the existing technologies. We shall outline some of the developments in the laser field, required to achieve potential future technological goals.

Passive Q-switched cw diode-pumped Nd-doped YAG and YVO4 lasers

CW diode pumped solid state lasers have sought for various scientific, medical and military applications, where compact reliable, stable, and highly efficient sources are desirable. There are several applications such as fiber- optic sensing or range finding which require short bursts of high peak power densities at multi-kilohertz repetition rates, and with a good beam quality. An extensive research on the properties of passively Q-switched, CW diode-pumped, ND-lasers has been conducted. We have used various pumping schemes to diode pump the Q-switched Nd:YAG and Nd:YVO4 laser crystals. Such schemes are transverse pumping by a cylindrical microlens-coupled diode array or longitudinally pumping by a fiber-coupled diode array. The passive Q- switching elements were Cr4+:YAG (polished, uncoated) and Cr4+:GGG (polished, coated), which were inserted inside the laser resonator. The 1.06 micrometers laser emission shows a repetitive modulation in the kHz frequency domain, and temporal bandwidth, full width at half maximum, in the range of 50 - 600 nsec. The modulation frequency and bandwidth depend on the characteristics of the Q-switching material (e.g. Cr4+ concentration, sample thickness) and on the input power level of the diode array used. We shall report design parameters and performance of various types of passively Q-switched and free-running diode pumped Nd-lasers. We shall present and discuss methods to increase the efficiency of Q-switched solid state lasers.

Studies of the spectroscopic behavior of Cr+3:LiCAF pumped by a solid-state dye laser

Abstract In this work we present spectroscopic studies of a laser system which combines transition metal-doped crystal pumped by a dye-doped solid-state laser. A dye-doped solid state laser emitting at ∼610 nm was chosen to allow a better fit into the absorption peak of the LiCAF crystal, peaking at ∼625 nm, in order to increase the efficiency of the light absorption of the Cr +3 ions. The pump laser is a dye-doped solid state laser Red Perylimide Dye (RPD)-doped in a composite-glass. This lasing maximum is at ∼608 nm with a threshold energy of ∼0.3 mJ/pulse, and a lasing slope efficiency of ∼2.5% under excitation of 532 nm Nd:YAG laser. With the excitation of dye-doped solid state laser the Cr +3 :LiCAF emission centered at ∼740 nm (due to the 4 T 2 xa0→xa0 4 A 2 transition) with lifetime of 170 μs and emission cross-section, σ f , of 1.4xa0×xa010 −20 cm −2 . The observed data allow us to plan a tunable Cr-crystal laser pumped by a solid-state dye laser.