Diode-Pumped Nd:KGd(WO4)2 Laser: Lasing at Fundamental and Second Harmonic Frequencies

Abstract

High-power cw and quasi-cw lasing at the fundamental and second harmonic frequencies is obtained from Nd:KGd(WO 4 ) 2 lasers based on N p -and N g -cut crystals pumped longitudinally by a diode laser at 879 nm. Because of different crystal lengths, the limiting pump power beyond which the crystals undergo thermomechanical damage is 26.8 W for the N p -cut and 17.3 W for the N g -cut. At these pump powers the cw outputs at λ = 1067.2 nm are 9.4 and 5.4 W, respectively, and the N g -cut crystal output is TEM 00 at the fundamental frequency. With quasicontinuous pumping at a 10% duty cycle the instantaneous laser power reaches ~11 W for both cuts with a periodic duration of 10-20 ms. The differential lasing effi ciency relative to the absorbed pump power is 66.4% for cw lasing and 77.4% for quasi-cw operation. With intracavity frequency doubling using a KTP crystal, better results were obtained with the N g -cut crystal because of its simpler thermal lensing. The maximum second harmonic power was ~1.1 W for cw operation and ~2.6 W for quasi-cw operation with a diode laser power of 27.3 W.Introduction. Of the solid-state matrices doped with trivalent rare-earth ions used as laser media and phosphors, crystalline potassium-gadolinium tungstate KGd(WO 4 ) 2 (referred to as KGW in the following) is exceptional. Crystalline KGW can be doped with isolated ions of Nd 3+ , Yb 3+ , Er 3+ , Ho 3+ , Tm 3+ , Pr 3+ , Dy 3+ , Eu 3+ [1][2][3][4][5][6][7] or their combinations, such as Er and Yb [8], Ho and Tm [9], Yb, Ho, Er, and Tm [10], etc. Since the ionic radius of the replaced Gd 3+ ion is close to the ionic radii of the other lanthanoids, the concentration of impurity centers in a KGW crystal can be quite high without causing signifi cant bulk deformations of the crystal lattice. For example, in the well known and easily available laser medium Nd:KGW the concentration of neodymium ion ranges from 3-10 at.%. In addition, the KGW matrix is active with respect to induced combination (Raman) scattering. Because of this, Nd:KGW lasers with fl ashlamp and diode pumping operate both at the fundamental wavelengths of the 4 F 3/2 -4 I 11/2 and 4 F 3/2 -4 I 13/2 transitions (1067.2 [11-13] and 1351 nm [14][15][16]) and at the wavelengths of the Stokes components owing to Raman self-conversion of the fundamental frequency (1180 [17], 1500 [18], and 1538 nm [19]). The combination of Raman conversion with the second harmonic (SH) generation or combination frequency effect makes it possible to obtain coherent light in the yellow region of the spectrum at wavelengths λ = 560 [20] and 590 nm [21] from Nd:KGW lasers.Nd:KGW lasers with frequency doubling of the fundamental at λ = 1.0672 μm have been discussed in the literature [22]. The distinctive feature of these lasers (λ l = 533.6 nm) is that they are suitable for optical pumping of Eu:KReW (where Re = Gd, Y, Lu) active media [7,23,24]. Pumping is in the 7 F 1 -5 D 1 absorption band of the europium ion. With pumping by a pulsed (Q-switched) frequency doubled Nd:KGW laser, for the fi rst...

Passive mode-locking of Nd:KGW laser with hot band diode pumping

“…Differential lasing (i.e. slope) efficiency for the Np-cut laser was reported ~66% with respect to the absorbed pump power [25]. A maximum fundamental output power of 7.0 W was achieved with 27 W of incident pump power in [45].…”

“…This excitation scheme has the lowest possible quantum defect in this particular system. Another possibility of low quantum defect pumping would be a direct in-band transition around 880 nm [25] corresponding to the excitation of an electron from the ground state to the emitting laser level 4 F3/2. In this case, however, the quantum defect will be larger than for the pumping wavelength around 910 nm.…”

Passive mode locking of a Nd:KGW laser with hot-band diode pumping

“…This excitation scheme has the lowest possible quantum defect in this particular system. Another possibility of low quantum defect pumping would be a direct in-band transition around 880 nm [13,28] corre sponding to the excitation of an electron from the ground state to the emitting laser level 4 F 3/2 . In this case, however, quantum defect will be larger than for the pumping wavelength around 910 nm.…”