Alexander Sabella

1240 nm diamond Raman laser operating near the quantum limit

An external-cavity diamond Raman laser generating up to 2.0 W at 1240 nm from 3.3 W of 1064 nm pump power is investigated as a function of pump polarization direction. The maximum conversion efficiency was 61%, and the slope efficiency of 84% closely approaches the quantum limit of 85.8%. The lowest threshold for Raman lasing is achieved for pump polarization parallel to the <111> axis, which we show is consistent with theory.

Highly efficient diamond Raman laser

We report an efficient 532 nm pumped external cavity diamond Raman laser generating output chiefly at the 573 nm first Stokes. At a pulse repetition rate of 5 kHz, the Raman laser generated 1.2 W output with a conversion efficiency of 63.5%, a slope efficiency of 75%, a pulse peak instantaneous conversion efficiency of 85%, and a peak photon conversion efficiency of 91%. The laser generated a maximum output energy of 0.67 mJ by increasing the pump beam size and the pulse energy. The efficiency is commensurate with the highest previously reported for other Raman materials pumped by Q-switched lasers.

Efficient conversion of a 1.064 μm Nd:YAG laser to the eye-safe region using a diamond Raman laser

We report an efficient 1.485 μm external cavity diamond Raman laser operating on the 2nd Stokes shift of a 1.064 μm Nd:YAG pump laser. 1.63 W pulsed at 5 kHz is produced with a quantum conversion efficiency of 71% and excellent beam quality. Numerical modelling confirms that optimal operation is achieved with low output coupling reflectivity.

Diamond Raman laser with continuously tunable output from 3.38 to 3.80 μm

We report a pulsed mid-infrared diamond Raman laser with output tuned from 3.38 to 3.80 μm through varying the optical parametric oscillator (OPO) pump wavelength. To our knowledge this is the longest reported wavelength from a solid-state Raman laser. We generated up to 80 μJ with good beam quality and 22% quantum conversion efficiency. Whilst the conversion process itself is efficient, approximately 40% of the generated Stokes light is lost to multiphonon absorption. By introducing a secondary pump beam at the anti-Stokes wavelength to initiate a seed at the Stokes wavelength through Raman resonant four-wave mixing, the laser threshold was reduced by approximately half, and the maximum output increased by 44% to 115 μJ.

Pump–Probe Measurements of the Raman Gain Coefficient in Crystals Using Multi-Longitudinal-Mode Beams

The effect of multi-longitudinal-mode interference on pump-probe Raman gain measurements is studied as the functions of laser linewidth and correlation between the pump and probe temporal structures. For Raman linewidths typical of crystals, correlations that develop between the pump and the probe increase the Raman amplification beyond the ideal single longitudinal mode case, leading to inflated Raman gain coefficient values. We show that the linewidth correction factors used previously are valid only for uncorrelated beams and small gain factors. Taking into account these considerations, a Raman gain coefficient for a diamond of 3.80 ± 0.35 cm/GW is reported at a pump wavelength of 1.864 μm (polarizations parallel to a 〈110〉 crystal axis).

Mid-infrared diamond Raman laser with tuneable output

We present an OPO pumped mid IR diamond Raman laser with tuneable output from 3.49 μm to 3.78 μm, which to our knowledge is the longest wavelength produced in a solid state Raman laser. Up to 59 μJ is generated with a conversion efficiency of 10%. We also determine the Raman gain coefficient of diamond at 1.864 μm through measurement of the amplification of a seed signal. With pump and probe polarisations aligned with the <110< crystal axes a value of 4.8 cm/GW is measured, which corresponds to 6.4 cm/GW for polarisation aligned with the <111< crystal axes. Achievable conversion efficiencies were limited by multi-phonon absorption at the Stokes wavelength. Numerical modelling shows that increasing the output coupling factor of the cavity reduces the impact of multi-phonon absorption and leads to higher conversion efficiencies. By reducing the output coupler reflectivity from 55% to 5% and eliminating Fresnel reflections from cavity components, 30% conversion efficiency (44% quantum conversion efficiency) is predicted.

Polarization conversion in cubic Raman crystals

Nonlinear conversion of unpolarized beams to lower frequencies is generally inefficient in c(2) materials, as it is challenging to achieve phase-matching for input ordinary and extraordinary beams simultaneously in the normal dispersion regime. Here, we show that cubic Raman crystals having doubly and triply degenerate (E and F type) modes provide a method for efficient nonlinear frequency downconversion of an unpolarized beam and yield a linearly polarized output state. Using Mueller calculus, optimal crystal directions for such polarization conversion are determined. Using diamond, an example of an F-class Raman crystal, we have verified that such conversion is possible with near quantum-defect-limited slope efficiency and a linear polarization contrast of more than 23.9 dB.

Efficient 1064 nm conversion to the eye-safe region using an external cavity diamond Raman laser

We present a 1064 nm pumped diamond Raman laser operating with 71% quantum conversion efficiency to the 2nd Stokes wavelength of 1485 nm. Up to 1.6 W average power is produced with excellent beam quality.

Design and characterisation of optical quality single crystal diamond for Raman laser applications

We report measurements of parameters important to Raman laser design for single crystal synthetic diamond. Raman laser operating space is assessed as functions of the pump wavelength, temporal format and design architecture.