Dual-rod Yb:YAG laser for high-power and high-brightness applications

Abstract

We describe a diode-pumped Yb:YAG laser producing 1080 W cw with 27.5% optical-optical efficiency and 532 W Q-switched with M2 =2.2 and 17% optical-optical eficiency.The laser uses two composite Yb:YAG rods separated by a 90 degree quartz rotator for bifocusing compensation. A microlensed diode array end-pumps each rod using a hollow lens duct for pump delivery. By changing resonator parameters, we can adjust thefindamental mode size and the output beam quality. Using a flattened gaussian intensity profile to calculate the modefill eficiency and clipping losses, we compare experimental data to modeled output power vs beam quality.High-average-power laser operation with good beam quality has long been an active area of development. Power oscillators offer greater simplicity compared to master-oscillator power-amplifier (MOPA) systems, but the finite TEMoa mode size possible' limits power scaling or results in multimode operation with lower beam quality. Considerable effort has been devoted to studying laser resonators to achieve high power and brightness.2T3A promising method to improve power scaling and reduce thermal effects is to minimize heat generation by the use of Yb3+ doped materials.4'5 lower heating rates compared to Nd3+, Although Yb3+ offers the quasi-three level nature of the laser transition requires careful engineering to achieve high power and efficiency."77%8 One of the challenges of designing a Yb3+ system is delivering pump light of sufficient intensity. In the diode-array end-pumped system described here, pump intensities >50 kW/cm2 enable efficient laser operation far above threshold. Correspondingly, high-average-power operation is achieved with a relatively small cross-section laser rod. This enables the laser rod to be the mode-limiting aperture in order to obtain good beam quality with high efficiency.Recently, very high brightness operation has been demonstrated from Nd:YAG laser oscillators incorporating a symmetric cavity with two identically pumped laser rods separated by a 90 degree quartz rotator for bifocusing compensation.' Here, we describe a similar resonator using two Yb:YAG laser rods. with a hollow lens duct for pump delivery," Diode-array end-pumping is used with the laser beam passing through each hollow lens duct and the two halves of the diode array.The composite laser rods have a 1 x 102' cme3 Yb-doped section, nominally 2 mm in diameter by 50 mm long, and flanged, undoped end caps. For this system, the laser rod diameter tapers along the length for parasitic suppression. l1 The diode arrays are made up of microlensed diode bars 1.5 cm long, mounted on silicon microchannel heatsink packages. l2 Each diode array contains 38 packages, resulting in > 4.56 kW total pump power. The diodes were operated with a cooling water temperature of 30 C to obtain the desired pump wavelength. The cooling water temperature of the laser rods was varied between 0 and 20 C. The resonator is symmetric, with the two laser rods separated by the 90 degree quartz rotator and a negative le...

Efficient, nanosecond self-Q-switched Cr,Yb:YAG lasers by bonding Yb:YAG crystal

“…The mechanically bonded Yb:YAG crystal and Cr,Yb:YAG crystal were held between two copper blocks. Six concave mirrors with 70-mm curvature and different transmissions (T OC ) of 5,10,20,30,40, and 50% at 1030 nm were used as output couplers. The cavity length is 70 mm.…”

“…Efficient laser performance of heavy doped Yb:YAG ceramics has been demonstrated recently [24,25]. High power laser-diode pumped Yb:YAG lasers based on Yb:YAG ceramics and crystals have been demonstrated with different laser resonator configuration such as thin disk lasers [26][27][28][29], rod lasers [30], microchip lasers [22,31], and slab lasers [32]. Yb:YAG ceramics have been successfully used to generate very-high order LaguerreGaussian modes by using a simple short-focus planoconvex glass lens [33] and circular modes by using a spherical intracavity lens [34].…”

Comparative study on enhancement of self-Q-switched Cr,Yb:YAG lasers by bonding Yb:YAG ceramic and crystal

“…Efficient laser performance of heavy doped Yb:YAG ceramics has been demonstrated recently [35,36]. High power laser-diode pumped Yb:YAG lasers based on Yb:YAG ceramics and crystals have been demonstrated with different laser resonator configuration such as thin disk lasers [37][38][39][40], rod lasers [41], microchip lasers [33,42], and slab lasers [43]. Yb:YAG ceramics have been successfully used to generate very-high order Laguerre-Gaussian modes by using a simple short-focus plano-convex glass lens [44] and circular modes by using a spherical intracavity lens [45].…”

High-brightness solid state laser systems with fiber phase conjugate mirrors for micro material processing

“…In addition, advanced crystal geometry (e.g. slab or disk laser) can be applied to reduce the induced phase distortions [1], [2]. In any case the remaining phase distortions have to be compensated with adaptive mirrors to facilitate near diffraction limited beam quality at average output powers of several hundred Watt.…”