Synchronously pumped continuous-wave mode-locked yellow Raman laser at 559 nm

Numerical analysis of synchronously pumped solid-state Raman lasers

Considering the spatial distribution of laser beams and phonon waves, the SRS coupling wave equations in the transient regime are derived and normalized for the first time. The synchronously pumped solid-state Raman laser is simulated numerically to investigate the influences of the cavity length detuning, output coupling rate, dispersion, Raman gain and dephasing time of Raman mode on laser performances. It is found that the intensive pulse compression of first Stokes laser in synchronously pumped solid-state Raman laser stems from pulse width gain narrowing and intensity oscillation effects. The cavity length detuning, dispersion, Raman gain and dephasing time considerably affect the pulse width gain narrowing and intensity oscillation processes. The theoretical results can help the design and optimization of synchronously pumped solid-state Raman laser to generate ultrafast Raman laser output efficiently.

All-fiber 1125 nm spectrally selected subnanosecond source

In this paper, we demonstrate the selection of radiation from the stimulated Raman scattered radiation, while using a spectral filter, based on a high-reflection fiber Bragg grating and an optical circulator. As a result, a stable pulsed signal was obtained at a wavelength of 1125 nm with a repetition rate of 1 MHz. The pulse duration and energy varied from 120 to 173 ps and 9 to 15 nJ, respectively, depending on the operating regimes of the master oscillator and amplifier.

Stimulated Raman Scattering in Yttrium, Gadolinium, and Calcium Orthovanadate Crystals with Single and Combined Frequency Shifts under Synchronous Picosecond Pumping for Sub-Picosecond or Multi-Wavelength Generation around 1.2 µm

Comparative investigation of stimulated Raman scattering (SRS) characteristics in the YVO4, GdVO4, and Ca3(VO4)2 orthovanadate crystals at both low and high frequency anionic group vibrations is presented. It was found that GdVO4 is the most perspective for SRS generation on both the ν1 stretching and ν2 bending modes of internal anionic group vibrations with the strongest SRS pulse shortening under synchronous picosecond pumping. It is as a result of GdVO4‘s widest linewidth (17cm−1) of the homogeneously broadened scheelite-type component of the bending ν2 Raman line that led to the strongest SRS pulse shortening down to the dephasing time of the widest (scheelite-type) Raman mode at the secondary intracavity short-shifted SRS conversion. It allowed us to achieve SRS pulses with sub-picosecond duration under tens-of-picoseconds pumping due to the strongest 42-fold pulse shortening. Using the Ca3(VO4)2 crystal with essentially wider Raman lines (~50cm−1) did not allow us to generate SRS pulses shorter than 1 ps. It can be explained by inhomogeneous broadening of the Raman lines in Ca3(VO4)2 because of its structural disordering. Using the measured SRS pulse duration, the homogeneous broadening of the inhomogeneously broadened bending Raman line of Ca3(VO4)2 was estimated to be ~9cm−1. Among the orthovanadate crystals, the YVO4 crystal with the highest Raman gain and with homogeneously broadened Raman lines allowed us to realize the most efficient SRS lasing and SRS pulse shortening truly down to inverse half-width of the bending Raman line.

Investigating single-longitudinal-mode operation of a continuous wave second Stokes diamond Raman ring laser

We report a diamond Raman ring cavity laser resonantly pumped by a tunable Ti:sapphire continuous wave laser. We characterize the laser operation generating first Stokes output and, for the first time, generate second Stokes lasing at a maximum output power of 364 mW with 33.4% slope efficiency at 1101.3 nm. Single longitudinal mode operation is achieved for all first Stokes output powers, but only for lower output powers for second Stokes operation. We discuss possible reasons preventing single longitudinal mode operation.

Stimulated Raman Scattering in Alkali-Earth Tungstate and Molybdate Crystals at Both Stretching and Bending Raman Modes under Synchronous Picosecond Pumping with Multiple Pulse Shortening Down to 1 ps

Comparative investigation of characteristics of spontaneous and stimulated Raman scattering (SRS) in different alkali-earth tungstate and molybdate crystals at both high and low frequency anionic group vibrations is presented. It has been found that, among these crystals, the SrMoO4 and SrWO4 crystals are the most perspective for SRS generation on both stretching and bending modes of internal anionic group vibrations with the strongest SRS pulse shortening under synchronous laser pumping because of not only highly intense stretching mode Raman line for efficient primary extra cavity long-shifted SRS conversion but also the widest bending mode Raman line for the strongest SRS pulse shortening down to the inverse width of the widest Raman line (~1 ps) at secondary intracavity short-shifted SRS conversion. The strongest 26-fold pump pulse shortening down to 1.4 ps at the Stokes component with the combined Raman shift in the synchronously pumped extra cavity SrMoO4 and SrWO4 Raman lasers has been demonstrated. It was found that synchronously pumped cascade SRS with combined Raman shift is more efficient in the SrWO4 crystal because the bending mode Raman line is more intense relative to the stretching mode Raman line than that in SrMoO4.

Compact KGd(WO4)2 picosecond pulse-train synchronously pumped broadband Raman laser

We demonstrate an efficient approach to realizing an extra-cavity, synchronously pumped, stimulated Raman cascaded process under low repetition frequency (1 kHz) pump conditions. We also construct a compact KGd(WO₄)₂ (KGW) crystal picosecond Raman laser that has been configured as the developed method. A pulse-train green laser pumped the corresponding 70 mm long KGW crystal Raman cavity. The pulse train contains six pulses, about 800 ps separated, for every millisecond; thus, it can realize synchronous pumping between pump pulse and the pumped Raman cavity. The investigated system produced a collinear Raman laser output that includes six laser lines covering the 532 to 800 nm spectra. This is the first report on an all-solid-state, high-average-power picosecond collinear multi-wavelength (more than three laser components) laser to our knowledge. This method has never been reported on before in the synchronously pumped stimulated Raman scattering (SRS) realm.

Ultrafast second-Stokes diamond Raman laser

We report a synchronously-pumped femtosecond diamond Raman laser operating with a tunable second-Stokes output. Pumped using a mode-locked Ti:sapphire laser at 840-910 nm with a duration of 165 fs, the second-Stokes wavelength was tuneable from 1082 - 1200 nm with sub-picosecond duration. Our results demonstrate potential for cascaded Raman conversion to extend the wavelength coverage of standard laser sources to new regions.

25.5 fs dissipative soliton diamond Raman laser

We have demonstrated a dissipative soliton diamond Raman laser that generates 25.5 fs pulses. Synchronously pumped by a 128 fs Ti:sapphire laser, the Raman cavity employed a pair of chirped mirrors to optimize the group delay dispersion, resulting in a Stokes field with 125 nm of spectral bandwidth from 840 to 965 nm. The Stokes pulse formation can be described as a dissipative soliton balancing self-phase modulation, normal dispersion, and gain due to stimulated Raman scattering (SRS).

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.

All-fiberized synchronously pumped 1120 nm picosecond Raman laser with flexible output dynamics

A largely simplified and highly efficient all-fiber-based synchronously pumping scheme is proposed. The synchronization between pump light and the cavity round-trip can be achieved by adjusting the repetition rate of pumping light without the requirement of altering the cavity length. Based on this scheme, we achieved generating narrow linewidth highly efficient 1120 nm pulse directly from an all-fiber Raman cavity. By pump repetition rate detuning and pump duration adjustment, the duration of the 1120 nm pulse can be widely tuned from 18 ps to ~1 ns, and the repetition rate can be adjusted from 12.41 MHz to 99.28 MHz by harmonic pumping. Up to 4.3 W high power operation is verified based on this scheme. Owing to the compact all-fiber configuration, the conversion efficiency of the 1066 nm pump light to the 1120 nm Stokes light exceeds 80% and the overall conversion efficiency (976 nm-1066 nm-1120 nm) is as high as 53.7%. The nonlinear output dynamics of the Raman laser are comprehensively explored. Two distinct operation regimes are investigated and characterized.

Picosecond 554 nm yellow-green fiber laser source with average power over 1 W

We demonstrate a source of 554 nm pulses with 2.7 ps pulse duration and 1.41 W average power, at a repetition rate of 300 MHz. The yellow-green pulse train is generated from the second harmonic of a 1.11 μm fiber laser source in periodically-poled stoichiometric LiTaO3. A total fundamental power of 2.52 W was used, giving a conversion efficiency of 56%.

Ti:sapphire-pumped diamond Raman laser with sub-100-fs pulse duration

We report a synchronously pumped femtosecond diamond Raman laser operating at 895 nm with a 33% slope efficiency. Pumped using a mode-locked Ti:sapphire laser at 800 nm with a duration of 170 fs, the bandwidth of the Stokes output is broadened and chirped to enable subsequent pulse compression to 95 fs using a prism pair. Modeling results indicate that self-phase modulation drives the broadening of the Stokes spectrum in this highly transient laser. Our results demonstrate the potential for Raman conversion to extend the wavelength coverage and pulse shorten Ti:sapphire lasers.

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.

Theoretical and experimental research on the polarization-coupled-input Raman oscillator

We present a polarization-coupled-input Raman oscillator, which is pumped by a 532 nm Q-switched hybrid resonator Nd:YVO(4) slab second harmonic generation laser. By the polarization-coupled method, the dichroic mirror is avoided and more than 98% of the 532 nm pump energy can be coupled into the Raman oscillator. Theoretical calculations and the experimental results show that the second Stokes effect is dramatically suppressed. With this method, the pure 559 nm (P(532)/P(559)<0.7% and P(589)/P(559)<0.1%) laser output can be achieved.

Deep ultraviolet diamond Raman laser

We present a synchronously pumped diamond Raman laser operating at 275.7 nm pumped by the 4th harmonic of a mode locked Nd:YVO4 laser. The laser had a threshold pump pulse energy of 5.8 nJ and generated up to 0.96 nJ pulses at 10.3% conversion efficiency. The results agree well with a numerical model that includes two-photon absorption of the pump and Stokes beams and uses a Raman gain coefficient of diamond of 100 cm/GW. We also report on the observation of nanometer scale two-photon assisted etching of the diamond crystal surfaces.

Thermo-optic coefficients and thermal lensing in Nd-doped KGd(WO4)2 laser crystals

We measured the thermo-optic coefficients dn/dT of anisotropic Nd:KGd(WO(4))(2) crystals at the wavelengths of 1.064 μm and 532 nm (300 K) by a beam deflection method. The values of dn/dT are determined to be dn(p)/dT = -16.0 × 10(-6) K(-1), dn(m)/dT = -11.8 × 10(-6) K(-1), and dn(g)/dT = -19.5 × 10(-6) K(-1) (at 1.064 μm) and dn(p)/dT = -14.3 × 10(-6) K(-1), dn(m)/dT = -10.0 × 10(-6) K(-1), and dn(g)/dT = -15.0 × 10(-6) K(-1) (at 532 nm). Thermal lensing in the flashlamp-pumped N(p)- and N(g)-cut Nd:KGd(WO(4))(2) laser rods was studied at 1.064 μm by a probe beam technique in the nonlasing conditions, and the contribution of the photoelastic term to the thermal lens optical power was estimated. Athermal propagation directions with the definitions dn/dT + (n-1)α(T) = 0 and dn/dT + nα(T) = 0 were found in Nd:KGd(WO(4))(2).

Pulse compression in synchronously pumped mode locked Raman lasers

We explain a pulse compression mechanism reported in picosecond Raman lasers pumped by continuous trains of mode-locked pulses. Our theoretical model is based on transient Raman scattering equations, and shows good agreement with the experimental results. The model reveals that the compression effect is produced by a combination of group velocity walk-off and strong pump pulse depletion. We predict the possibilities and the limitations of this technique for constructing highly efficient, low cost, ultrafast Raman lasers in the visible.

Multi-wavelength, all-solid-state, continuous wave mode locked picosecond Raman laser

We demonstrate the operation of a cascaded continuous wave (CW) mode-locked Raman oscillator. The output pulses were compressed from 28 ps at 532 nm down to 6.5 ps at 559 nm (first Stokes) and 5.5 ps at 589 nm (second Stokes). The maximum output was 2.5 W at 559 nm and 1.4 W at 589 nm with slope efficiencies up to 52%. This technique allows simple and efficient generation of short-pulse radiation to the cascaded Stokes wavelengths, extending the mode-locked operation of Raman lasers to a wider range of visible wavelengths between 500 - 650 nm based on standard inexpensive picosecond Nd:YAG oscillators.

Mode-locked picosecond diamond Raman laser

We present a mode-locked diamond Raman laser synchronously pumped by a mode-locked laser running at 532 nm and pulse duration 26 ps. The diamond laser generated up to 2.2 W of average power with output pulses of duration 21 ps at a yellow wavelength of 573 nm. The output pulse duration varied notably with small changes in cavity length and decreased to a minimum of 9 ps. The power and pulse duration behavior as a function of cavity length is explained well by a model that includes phonon dephasing and group velocity dispersion of the pump and Stokes fields.