Intra-cavity second-harmonic and sum-frequency generation in a diode-pumped broadband Yb-doped fibre laser

Intra-cavity nonlinear frequency mixing in a diode-pumped, broadband Yb-doped fibre laser has been investigated. Second-harmonic generation of the fibre output, second-harmonic generation of the residual pump beam and sum frequency mixing between the two was achieved simultaneously, resulting in three colour operation in the blue-green region. Including the nonlinear crystal inside the cavity is also shown to be effective in reducing fluctuations in the output power.     

Highly efficient narrow-line generation by difference-frequency mixing of a green pump and the stokes seed in RbTiOPO4 crystals: excitation of 943-nm emission

An efficient and compact scheme for diode-pumped Nd:YLF laser wavelength conversion to 943 nm was demonstrated by use of difference-frequency mixing and stimulated Raman scattering. We believe that this is the highest conversion efficiency from the laser fundamental wavelength reported to date. It is shown that RbTiOPO4 crystals are capable of providing highly efficient frequency mixing as a nonlinear medium.     

Efficient generation of tunable VUV laser radiation below 205 nm by SFM in BBO

Design and performance characteristics of a tunable dye laser system for sum frequency mixing (SFM) in a BBO crystal are presented. The system is composed of two tunable pulsed dye lasers pumped synchronously by the second harmonic of a commercial Nd:YAG laser. The radiation produced by the first dye laser is frequency doubled by second-harmonic generation (SHG) in KDP and subsequently mixed by SFM in BBO with the light of the second dye laser. The interest was focussed on generation of tunable laser radiation below 205 nm with high output power and long-time wavelength stability. High conversion efficiencies enable output energies of 100 J (20 kW) at 196 nm using only moderate Nd:YAG pump energies of 67 mJ. Altogether, a laser system with very good specifications for analytical application in the near VUV spectral region is reported.     

Thermal loss mechanism in the generation of multifrequency laser emission via stimulated Raman scattering and four-wave Raman mixing studied by photothermal refraction spectroscopy

The heat produced in conjunction with the processes of stimulated Raman scattering and four-wave Raman mixing in hydrogen was measured by photothermal refraction spectroscopy. Many vibrational, rotational, and vibrationally shifted rotational Raman lines are exclusively/simultaneously generated by changing the polarization of the laser beam and the hydrogen pressure. Thermal loss occurs predominantly from vibrational Raman scattering, which can be ascribed to a large Raman shift frequency of 4155 cm^-1 for the vibrational transition. In contrast to stimulated Raman scattering, little or no thermal loss is observable during the process of four-wave Raman mixing. Received: 12 April 1999 / Revised version: 12 July 1999 / Published online: 20 October 1999     

Modeling and experimental investigation of short pulse Raman microchip laser

The results of experimental and theoretical investigations of passive Q-switch Raman microchip lasers based on Nd³⁺:LSB active medium and Ba(NO₃)₂ Raman crystal are presented. It has been demonstrated that intracavity Raman conversion in the microchip lasers is a simple and efficient method, capable of delivering high power pulses with sub-100 ps duration. Intracavity generation of the 1st Stokes pulses with duration from 180 down to 48 ps and a peak power of 48 kW has been performed and studied. High peak power and short duration of the 1st Stokes pulses in microchip laser with Ba(NO₃)₂ Raman crystal allows to easily perform extracavity harmonic generation and frequency sum mixing in LBO, BBO, and KTP crystals with discrete-tunable wavelength from ∼1200 down to ∼240 nm. We have developed a generalized model of Q-switched Raman microchip lasers, that takes into account spatial inhomogeneity of pump, laser, and Stokes beams, thermalization within the upper and lower multiplets of activator ions in laser medium, and saturable absorber bleaching and recovery. For the microchip lasers with different saturable absorbers, the model achieves very good agreement with the presented experimental results in a wide range of pump powers.     

All-solid-state doubly resonant intracavity frequency sum mixing orange yellow laser with 3.2 W output power at 593.5 nm

A compact and efficient 593.5 nm orange-yellow laser is realized using doubly resonant intracavity sum frequency mixing. Two Nd: YVO₄ crystals are employed as the gain crystals. In two sub-cavities, 1064 nm radiation from one Nd: YVO₄ and 1342 nm radiation from the other Nd: YVO₄ are mixed to generate 593.5 nm orange-yellow laser. In the overlapping of the two cavities, sum frequency mixing is achieved in a type I critical phase matching (CPM) LBO crystal. An output power of 3.2 W at the wavelength of 593.5 nm is obtained with total incident pump power of 38 W. The optical to optical conversion efficiency is up to 8.4% and the stability of the output power is better than 2.48% in 8 h. To the best knowledge, this it the highest watt-level laser at 593.5 nm generated by diode end pump all-solid-state technology.     

Frequency doubling of a Raman fiber laser

655 nm laser radiation with power of >60 mW is generated by frequency doubling of a broadband randomly-polarized 1.31-μm phosphosilicate Raman fiber laser (RFL). The red power appears to grow linearly with increasing RFL power up to 7 W at efficiency comparable with that for single-frequency lasers. It has been shown that multiple sum-frequency mixing processes involving different RFL modes provide the main contribution to the output, which is enhanced by 2 times due to the modes stochasticity.     

Generation of tunable picosecond pulses in the ultraviolet region down to 197 nm

Tunable picosecond pulses in the ultraviolet region down to 197 nm with ? 20 kW peak power are generated by the sum frequency mixing of fourth or third harmonic pulses of a mode-locked YAG laser with tunable pulses produced by a LiNbO₃ parametric oscillator pumped by second harmonic pulses of the YAG laser by using a KB5 or KDP crystal.     

Stimulated Raman scattering in a potassium titanyl phosphate crystal: simultaneous self-sum frequency mixing and self-frequency doubling

A potassium titanyl phosphate crystal is used to achieve efficient stimulated Raman scattering conversion with simultaneous self-sum frequency mixing and self-frequency doubling. Inside a diode-pumped Nd:YAG Q-switched laser cavity, 1.03 W of 1129-nm second Stokes average output power and 0.25 W of 548-nm sum-frequency average power are simultaneously generated with a diode input power of 10 W at a pulse repetition rate of 10 kHz.     

LD抽运腔内和频571.6 nm连续波黄光激光器

报道了全固态连续波571.6 nm黄光激光器.黄激光是分别由两片Nd∶YAG的1 444 nm和946 nm谱线非线性和频产生,两条谱线在各自晶体对应能级跃迁分别为4F3/2-4I15/2和4F3/2-4I9/2.实验中采用复合腔结构,利用RTP晶体II类临界相位进行内腔和频,当注入到两片Nd∶YAG晶体的抽运功率分别为25 W和14.8 W时,获得562 mW的连续波571.6 nm黄激光输出,4 h功率稳定度优于±2.9％.     

Tunable far-infrared generation by difference frequency mixing in InSb

Far-infrared radiation tunable over the range 85–105 cm^-1 and at power levels of up to 10 μW has been generated by difference frequency mixing in InSb. The infra-red radiations which are mixed are a 10.6 μm TEA-CO₂ laser line and the tunable Stokes radiation produced from it by spin-flip Raman-laser action, again in an InSb sample. It is argued that careful choice of the free-carrier concentrations in the crystals used for (a) the Stokes generation and (b) the mixing, or the application of an electric field across the mixing sample, should considerably improve the far-infrared power levels.     

Nonlinear-optical transformation of nanosecond laser pulses and controlled supercontinuum generation in photonic-crystal fibers

Photonic-crystal fibers are shown to allow efficient spectral transformation of nanosecond laser pulses through parametric four-wave mixing and stimulated Raman scattering. Regimes providing highly efficient transformation of nanosecond laser pulses into white-light broadband radiation (supercontinuum) are identified. A strong parametric coupling between Stokes and anti-Stokes Raman sidebands around the wavelength of zero group-velocity dispersion is shown to increase the bandwidth and to improve the spectral quality of supercontinuum radiation.     

High-power supercontinuum generation in highly nonlinear, dispersion-shifted fibers by use of a continuous-wave Raman fiber laser

High-power supercontinua are demonstrated in highly nonlinear, dispersion-shifted fibers with a continuous-wave Raman fiber laser. Supercontinuum growth is experimentally studied under different combinations of fiber length and launch power to show output powers as high as 3.2 W and bandwidths greater than 544 nm. Modulation instability (MI) is observed to seed spectral broadening at low launch powers, and the interplay between MI and stimulated Raman scattering plays an important role in the growth of the continuum at high launch powers. The effect on continuum generation of parametric four-wave mixing coupled with the higher-order dispersion properties of the fiber is investigated.     

Cascaded four-wave mixing generation in photonic crystal fibers

We investigate the efficient generation of broadband cascaded four-wave mixing products seeded at different wavelengths in photonic crystal fibers, with a high-peak power picosecond pulse pumping in the anomalous dispersion region as well as the normal dispersion regime. Multiple four-wave mixing products with different frequency intervals have been experimentally achieved when pumping in the anomalous dispersion region. Measured results present bandwidths of over 500 nm. We have also experimentally demonstrated that only seeding at the Stokes or anti-Stokes peaks can we get the efficient generation of cascaded four-wave mixing or cascaded stimulated Raman scattering when pumping in the normal dispersion regime.     

Generation of continuous-wave 243-nm radiation by sum-frequency mixing

We have generated tunable cw radiation near 243 nm with a linewidth of less than 4 MHz by sum-frequency mixing the 351 nm radiation from an argon-ion laser with the 789 nm radiation from a ring dye laser in a crystal of ammonium dihydrogen phosphate held at moderate temperature. An external ring cavity, resonant with the dye laser, gives a power enhancement of about 12 in the sum-frequency generated radiation. Thermal lensing due to laser heating of the nonlinear crystal, distorded the 351 nm mode structure. This effect could limit the efficiency of the sum frequency mixing process.     

A pulsed laser system with large spectral coverage extended by non-linear frequency conversion

We report on an injection-seeded Ti:sapphire laser pumped by the second harmonic of a Nd:YAG laser. Due to an excellent spatial beam profile and narrow linewidth near the Fourier transform limit we are able to achieve high conversion efficiencies and stable output power in harmonic generation as well as in sum and difference frequency mixing with the pump pulse. The laser system can potentially cover a spectral range from 190 to over 6000 nm.     

Coherent bisection of 141 THz using sum frequency generation of 1064 and 709 nm radiation

The frequency interval (141 THz) that exists between 1064 nm radiation and the unusual semiconductor wavelength of 709 nm has been coherently divided by using an optical phase-locked loop to control a slave laser lying at the mean frequency of these two wavelengths. The 709 nm radiation has been generated by a combination of wavelength tuning in an extended cavity and temperature tuning of a ridge-waveguide semiconductor laser with a nominal wavelength of 728 nm. Two nonlinear processes have been used to produce the coherent division: the sum frequency mixing of 1064 and 709 nm radiation to produce 425 nm radiation and the second harmonic generation of 851 nm light to produce the same wavelength radiation.     

Continuous-wave Raman generation in a diode-pumped Nd3+:KGd(WO4)2 laser

Continuous-wave Raman generation in a compact solid-state laser system pumped by a multimode diode laser is demonstrated. The Stokes radiation of stimulated Raman scattering at 1.181 microm is generated as a result of self-frequency conversion of the 1.067 microm laser radiation in Nd3+:KGd(WO4)2 crystal placed in the cavity. The Raman threshold was measured at 1.15 W of laser diode power. The highest output power obtained at the Stokes wavelength was 54 mW. The anomalous delay of Raman generation relative to the start of laser generation (the oscillation buildup) due to slow accumulation of Stokes photons in the cavity at low Raman gain and Raman threshold dependence not only on the laser intensity but also on the time of laser action are observed.     

Inhomogeneous loss mechanism in multiwavelength fiber Raman ring lasers

As one of the mechanisms for stable multiwavelength oscillation in a fiber Raman ring laser, an inhomogeneous loss induced by intraline four-wave mixing in a fiber Raman laser is physically explained and experimentally validated by comparison of laser peak gain and power gain as well as the gain spectra at several pump levels.     

Phase matching and focussing effects in noncollinear sum frequency mixing in the near VUV region

We demonstrate that focussing effects are extremely important in determining the bandwidth in sum frequency mixing of ultrashort pulses in the near VUV region. This effect is demonstrated with noncollinear sum frequency mixing performed between the fundamental and the third harmonic subpicosecond pulses of a Ti:sapphire laser. The spectrum of the generated fourth harmonic radiation is significantly broader (by 33%) than the theoretical spectrum obtained if focussing is not taken into account. We have developed a method of calculating the output bandwidth for sum frequency mixing of broadband spectral envelopes whose bandwidths correspond to ultrashort optical pulses, including focussing. The calculated and the measured spectra show excellent agreement.