Thermal aberrations and high power frequency conversion in a barium nitrate Raman laser

Chulkov, R. V.; Lisinetskii, V. A.; Lux, Oliver; Rhee, H.; Schrader, Sigurd; Eichler, Hans-Joachim; Orlovich, V. A.

doi:10.1007/s00340-012-4873-4

Cited by 21 publications

(18 citation statements)

References 26 publications

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“…Since the first use of CVD diamond in Raman laser oscillators in 2008 , the achieved average power‐levels in this material have grown at a rapid rate, with nanosecond‐pulsed devices reaching 1 W in 2009 and 24.5 W in late 2010 , and CW systems achieving 5–10 W in 2012 and 108 W (quasi‐CW, 250

μ s

pulsed) in 2014 . In contrast, average power scaling in conventional Raman crystals is much more challenging due to strong thermal effects arising from the inelastic Raman scattering process, and levels are presently limited to less than 20 W . In diamond, the onset of thermal effects is expected to occur at average power levels several orders of magnitude higher (for all other design parameters equal) according to the much‐higher thermal conductivity and a low thermal expansion coefficient (

1.1 \times 10^{- 6}

K −1 ) .…”

Section: Introductionmentioning

confidence: 99%

Efficient Raman frequency conversion of high‐power fiber lasers in diamond

Williams

Nold

Strecker

et al. 2015

Laser & Photonics Reviews

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We report high-power frequency conversion of a Yb-doped fiber laser using a double-pass pumped external-cavity diamond Raman oscillator. Pumping with circular polarization is shown to be efficient while facilitating high-power optical isolation between the pump and Raman laser. We achieved continuous-wave average power of 154W with a conversion efficiency of 50.5% limited by backward-amplified light in the fiber laser. In order to prove further scalability, we achieved a maximum steady-state Raman-shifted output of 381W with 61% conversion efficiency and excellent beam quality using 10ms pump pulses, approximately a thousand times longer than the transient thermal time-constant. No power saturation or degradation in beam quality is observed. The results challenge the present understanding of heat deposition in Raman crystals and foreshadow prospects for reduced thermal effects in diamond than originally anticipated. We also report the first experimental evidence for stimulated Brillouin scattering in diamond. Diamond is used for Raman beam conversion of a 700 W Yb fiber laser, achieving record conversion efficiency (>60%) and output power (380 W). High beam quality and efficient conversion at high powers-in stark contrast to predictions for the thermal lens and cavity stability-challenge the current understanding of heat deposition in diamond Raman lasers. Experimental evidence for stimulated Brillouin scattering in diamond is reported

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μ s

1.1 \times 10^{- 6}

K −1 ) .…”

Section: Introductionmentioning

confidence: 99%

Efficient Raman frequency conversion of high‐power fiber lasers in diamond

Williams

Nold

Strecker

et al. 2015

Laser & Photonics Reviews

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“…Significant improvements in beam quality from the pump were achieved with brightness enhancement factors much greater than unity . Crystal Raman lasers have more recently been of interest to enable Raman shifting from smaller systems free of gas handling, and to exploit their higher thermal conductivity to extend output to higher average powers . However, despite the well‐known effect of Raman beam cleanup, a pump laser with excellent beam quality has been seen as an important requirement for efficient operation (e.g., ).…”

Section: Introductionmentioning

confidence: 99%

Simultaneous brightness enhancement and wavelength conversion to the eye‐safe region in a high‐power diamond Raman laser

McKay

Kitzler

Mildren

2014

Laser & Photonics Reviews

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Brightness enhancement in an external cavity diamond Raman laser designed for high power conversion of a neodymium (1064 nm) laser to the eye‐safe spectral region is reported. Using a multimode input beam pulsed at 36 kHz pulse repetition frequency, 16.2 W with 40% overall conversion efficiency was obtained at the second Stokes wavelength of 1485 nm. The output beam had a quality factor of M2=1.17±0.08 which is a factor of 2.7 times lower than that of the input beam, resulting in a higher overall brightness. The output power, brightness, and brightness enhancement obtained represent significant advances in performance for Raman lasers as well as other competing kHz‐pulsed eye‐safe technologies.

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“…In molecular ion Raman crystals, such as the alkali or alkalis-earth nitrates and tungstates, thermal effects are evident even for average output powers around the single or multi-watt level [2,3]. Higher powers (>5 W) have been obtained by compensating for lensing in the resonator design [4,5], or using materials with improved thermal characteristics such as barium tungstate [6,7] and diamond [8][9][10][11]. As part of the on-going drive for higher powered devices, it is important to understand how the crystal heating affects performance and to determine methods for compensation or circumvention.…”

Section: Introductionmentioning

confidence: 99%

Thermal lens evolution and compensation in a high power KGW Raman laser

McKay¹,

Kitzler²,

Mildren³

2014

Opt. Express

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The transient thermal lens in a high-average power double metal tungstate Raman laser has been investigated. An external cavity potassium gadolinium tungstate (KGW) laser designed for second-Stokes output was burst-pumped with up to 46 W of average power at a pulse repetition rate of 38 kHz. At low duty-cycle, the laser generated up to 18 W of on-time average Raman power with a conversion efficiency of 40%. At high duty cycle, efficiency is reduced and the near-field beam profile expands in the X1' crystal direction over a period of tens of milliseconds. The evolution of the spatial beam properties occurs in response to the development of a highly astigmatic thermal lens with fast-axis susceptibility of approximately -1.7 m-1 per watt of Raman output power. We show that the likely cause for astigmatism is primarily photo-elastic in origin. Beam circularization was achieved by incorporating an intracavity convex cylindrical lens.

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Thermal aberrations and high power frequency conversion in a barium nitrate Raman laser

Cited by 21 publications

References 26 publications

Efficient Raman frequency conversion of high‐power fiber lasers in diamond

Efficient Raman frequency conversion of high‐power fiber lasers in diamond

Simultaneous brightness enhancement and wavelength conversion to the eye‐safe region in a high‐power diamond Raman laser

Thermal lens evolution and compensation in a high power KGW Raman laser

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