Investigation of intracavity MgO:LiNbO3 terahertz polariton laser gain over an extended 1-5 THz range.

Most intracavity MgO:LiNbO3 terahertz polariton lasers generate output in the 1-3 THz range. In this study, we investigate the potential to extend this tuning range toward 6 THz. We predict broader tuning using a modified polariton gain theory that takes account of additional polariton damping at 3.15 THz and the angle-dependent field overlap in the crystal. We achieved continuous tuning between 1.5 and 5.4 THz and characterised the gain in this range-so far the widest THz frequency range achieved from a nonlinear crystal via intracavity SPS.

Monte Carlo modelling for elastic and Raman signals in oceanic LiDAR.

We investigate Raman returns in oceanic light detection and ranging (LiDAR), and explore the similarities and differences to conventional elastic returns. We show that Raman returns have much more complex behavior than elastic returns, which likely cannot be well matched by simple models, making Monte Carlo simulations essential. We investigate the correlation between the time of signal arrival and the depth of the Raman event, and find that a linear correlation only exists for judicious choice of system parameters.

Cavity design with single-mirror THz frequency tuning for polariton lasers.

We demonstrate a new, to the best of our knlowledge, cavity design for terahertz (THz) lasers based on stimulated polariton scattering (SPS). The design simplifies the angle tuning of these lasers, which require non-collinear cavity fields at fundamental and Stokes wavelengths to cross in an SPS crystal with adjustable crossing angle. A mirror shared by both the fundamental and Stokes cavities ensures stationary overlap of the fields within the crystal, with the angle between the fields tunable by adjustment of one axis of a single mirror. We demonstrate the design for an intracavity SPS laser using a rubidium titanyle phosphate (RTP) crystal, and achieve single-mirror tuning of the THz output in bands between 3 and 5.8 THz, with a maximum output of 78 µW at 4.08 THz.

Direct generation of 1108†nm and 1173†nm Laguerre-Gaussian modes from a self-Raman Nd:GdVO4 laser.

We demonstrate a continuous-wave self-Raman Nd:GdVO4 Laguerre-Gaussian (LG) mode laser based on different Raman shifts of 382 cm-1 and 882 cm-1 by shaping the pumping beam with the use of an axicon lens and a focusing lens. Selective generation of LG mode beams at 1108 nm or 1173 nm, or simultaneously 1108 nm and 1173 nm, was achieved by carefully adjusting the alignment of the laser cavity. The maximum Raman LG mode output powers at the wavelengths of 1108 nm (the first-Stokes emission of the 382 cm-1 Raman shift) and 1173 nm (the first-Stokes emission of the 882 cm-1 Raman shift) were measured to be 49.8 mW and 133.4 mW at the absorbed pump power of 5.69 W, respectively. The generated LG modes, formed via the incoherent superposition of two LG mode beams with positive and negative topological charges, carry zero orbital angular momentum. Such LG mode laser sources have the potential to fill in the wavelength gap of lasers in the visible and infrared regions.

A single-frequency intracavity Raman laser.

A continuous-wave (CW) single-longitudinal-mode (SLM) intracavity Raman laser is demonstrated for the first time, by virtue of the spatial hole-burning free nature of stimulated Raman scattering (SRS) gain. By using a single etalon in the Nd:GdVO4 fundamental laser cavity, the spectral linewidth of the multimode fundamental field is suppressed below the Raman linewidth of Raman crystal BaWO4; hence power in all the longitudinal modes of fundamental field can be extracted by one single Stokes mode. Therefore, the hole-burning free SRS gain exhibits a spectral cleanup effect whereby a stable SLM Stokes field is derived from the multimode fundamental field within a simple standing-wave cavity arrangement. The low-threshold SLM Raman laser delivered 3.42 W SLM Stokes and 1.53 W SLM one-way yellow harmonic at the guide-star wavelength of 589.16 nm. The results here provide a new approach to SLM laser operation with good simplicity and power dynamic range. Further engineering for power scaling and better stability is also discussed.

Tunable THz polariton laser based on 1342 nm wavelength for enhanced terahertz wave extraction.

We detail the operation of a THz laser source based on non-linear stimulated polariton scattering (SPS) in Mg:LiNbO3. This system utilizes a fundamental wavelength of 1342 nm to completely avoid the negative effect of free-carrier generation within high-resistivity silicon (Si) prisms used to extract THz radiation from the Mg:LiNbO3 crystal. THz power of up to 23.6 µW (62.3 µW when chopped at 50% duty cycle) was detected at 1.33 THz, and frequency tunability across the range 1.05-2.2 THz was achieved.

Single-longitudinal-mode ring diamond Raman laser.

We demonstrate a single-longitudinal-mode ring diamond Raman laser, pumped by a tunable single-mode Ti:sapphire laser. Two methods to achieving unidirectional operation have been demonstrated: increasing gain for one direction using a reinjecting mirror and increasing loss for one direction using sum frequency mixing in BBO. Both methods result in a stable single-longitudinal-mode operation.

THz polariton laser using an intracavity Mg:LiNbO3 crystal with protective Teflon coating.

An enhancement in the performance of a THz polariton laser based on an intracavity magnesium-doped lithium niobate crystal (Mg:LiNbO3) in surface-emitted (SE) configuration is demonstrated resulting from the deposition of a protective Teflon coating on the total internal reflection surface of the crystal. In this cavity geometry the resonating fields undergo total internal reflection (TIR) inside the lithium niobate, and laser damage to that surface can be a limiting factor in performance. The protective layer prevents laser damage to the crystal surface, enabling higher pump power, yielding higher THz output power and wider frequency tuning range. With the unprotected crystal, narrow-band THz output tunable from 1.50 to 2.81 THz was produced, with maximum average output power of 20.1 µW at 1.76 THz for 4 W diode pump power (limited by laser damage to the crystal). With the Teflon coating, no laser damage to the crystal was observed, and the system produced narrow-band THz output tunable from 1.46 to 3.84 THz, with maximum average output power of 56.8 µW at 1.76 THz for 6.5 W diode pump power. This is the highest average output power and the highest diode-to-terahertz conversion efficiency ever reported for an intracavity terahertz polariton laser.

Tunable terahertz generation in the picosecond regime from the stimulated polariton scattering in a LiNbO3 crystal.

We demonstrate narrowband tunable terahertz generation from a picosecond LiNbO3 polariton laser, pumped by a CW mode-locked Nd:YVO4 picosecond laser. We generated up to 5.4 µW of terahertz output in untuned mode. We tuned the terahertz output, using etalons in the cavity, from 0.51 to 2.12 THz. Terahertz output powers of 3.7 µW and 2.4 µW were achieved at terahertz frequencies of 1.6 THz and 0.9 THz, respectively.

Stimulated polariton scattering in an intracavity RbTiOPO4 crystal generating frequency-tunable THz output.

A high power, frequency-tunable THz source based on intracavity stimulated polariton scattering (SPS) in RbTiOPO4 (RTP) is demonstrated for the first time. Frequency tunable THz output was obtained from 3.10 to 4.15 THz, with a gap at 3.17 to 3.49 THz, arising from the 104 cm-1 A1 mode in RTP. A maximum average output power of 16.2 µW was detected at 3.8 THz. This is the highest average output power ever reported for an intracavity polariton laser.

Multiwavelength ultrafast LiNbO(3) Raman laser.

We present a multiwavelength ultrafast Raman laser based on lithium niobate which uses polariton scattering in combination with Raman scattering to selectively generate new wavelengths from a nanojoule-scale picosecond pump laser. Pumped by a 1064 nm pump laser, the system generates 1123 nm by stimulated polariton scattering (SPS) and 1140 nm by stimulated Raman scattering (SRS). Cascading of these intracavity fields generates 1155 nm and 1174 nm, as well as generating THz output.

Diode-side-pumped continuous wave Nd³âº : YVO4 self-Raman laser at 1176 nm.

Here we report, to the best of our knowledge, the first diode-side-pumped continuous wave (cw) Nd3+:YVO4 self-Raman laser operating at 1176 nm. The compact cavity design is based on the total internal reflection of the laser beam at the pumped side of the Nd3+:YVO4 crystal. Configurations with a single bounce and a double bounce of the laser beam at the pumped faced have been characterized, providing a quasi-cw peak output power of more than 8 W (multimode) with an optical conversion efficiency of 11.5% and 3.7 W (TEM00) having an optical conversion efficiency of 5.4%, respectively. Cw output power of 1.8 W has been demonstrated.

Cascaded stimulated polariton scattering in a Mg:LiNbO(3) terahertz laser.

Cascaded Stimulated Polariton Scattering (SPS) to the fourth-Stokes order is observed experimentally in an intracavity THz polariton laser utilising Mg:LiNbO(3). The performance of the cascaded laser is presented, the origin of the cascaded fields is explained and compared to theory, and the potential consequences for using cascading to enhance the THz output from this type of device are discussed.

Intracavity frequency converted Raman laser producing 10 deep blue to cyan emission lines with up to 0.94 W output power.

Here we report 10 laser emission lines in the attractive deep blue to cyan spectral region from an intracavity frequency doubled Raman laser. The fundamental laser field that drives the Raman laser is based on the three-level transition of Nd:YLF. A maximum extracted quasi-continuous wave (qcw) output power of 0.94 W is achieved in the deep blue to cyan spectral regime.

Quasi-continuous wave Raman lasers at 990 and 976 nm based on a three-level Nd:YLF laser.

An intracavity Raman laser based on laser transition in Nd:YLF is reported. Quasi-continuous wave Stokes output power was observed at 990 and 976 nm, and up to 0.88 W of peak output power was obtained at 990 nm.

Spectral broadening in continuous-wave intracavity Raman lasers.

Spectral broadening of the fundamental field in intracavity Raman lasers is investigated. The mechanism for the spectral broadening is discussed and the effect is compared in two lasers using Raman crystals with different Raman linewidths. The impact of the spectral broadening on the effective Raman gain is analyzed, and the use of etalons to limit the fundamental spectral width is explored. It was found that an improvement in output power could be obtained by using etalons to limit the fundamental spectrum to a single narrow peak.

Highly efficient picosecond diamond Raman laser at 1240 and 1485 nm.

We present a highly efficient picosecond diamond Raman laser synchronously-pumped by a 4.8 W mode-locked laser at 1064 nm. A ring cavity was adopted for efficient operation. With a low-Q cavity for first-Stokes 1240 nm, we have achieved 2.75 W output power at 1240 nm with 59% overall conversion efficiency. The slope efficiency tended towards 76% far above the SRS threshold, approaching the SRS quantum limit for diamond. A high-Q first-Stokes cavity was employed for second-Stokes 1485 nm generation through the combined processes of four-wave mixing and single-pass stimulated Raman scattering. Up to 1.0 W of second-stokes at 1485 nm was obtained, corresponding to 21% overall conversion efficiency. The minimum output pulse duration was compressed relative to the 15 ps pump, producing pulses as short as 9 ps for 1240 nm and 6 ps for 1485 nm respectively.

An intracavity, frequency-doubled self-Raman vortex laser.

We demonstrate intracavity frequency doubling of the self-Raman field generated within a diode end-pumped, solid state Nd:GdVO(4) vortex laser. A maximum output power of 727 mW is generated at 586 nm with an overall diode-to-yellow conversion efficiency of 4%. Conservation of orbital angular momentum is observed under intracavity frequency doubling, with the topological charge of the yellow beam being twice that of the Stokes beam.

Continuous wave, frequency-tunable terahertz laser radiation generated via stimulated polariton scattering.

We report the generation of CW THz radiation, generated via stimulated polariton scattering in MgO:LiNbO3. The system is capable of producing frequency tunable radiation across the range 1.5-2.3 THz and requires only 2.3 W incident diode pump power to reach threshold. Maximum THz output power of 2.3 µW has been detected for just 5.9 W incident diode pump power, at a frequency of 1.8 THz.

Direct generation of a first-Stokes vortex laser beam from a self-Raman laser.

We demonstrate the direct generation of a first-order LG(01) Laguerre Gaussian (vortex) mode operating at the first-Stokes wavelength of a diode end-pumped, Nd:GdVO(4) self-Raman laser. To the best of our knowledge, this is the first report of intracavity stimulated Raman scattering (SRS) being used as a method for frequency conversion of a vortex laser beam and it is effective in enabling the frequency-converted (Stokes) beam to have the same LG(01) mode as the fundamental beam.