Frequency stabilization of a frequency-doubled 197.2 THz distributed feedback diode laser on rubidium 5S1/2→7S1/2 two-photon transitions

A 197.2 THz (1520.2 nm) ITU-T grid distributed feedback (DFB) diode laser is frequency stabilized at 197.198 THz by 1ocking its second harmonic (SH) signal on the rubidium 5S_1/2→7S_1/2 two-photon transition at 394.396 THz (760.1 nm). With 100 mW from the DFB diode laser and amplifying by an erbium-doped fiber amplifier, we obtain an SH power of 15 mW using a periodically poled lithium niobate (PPLN) waveguide frequency doubler. The stability was 2×10⁻¹¹ (10 s), corresponding to a frequency variation of 4 kHz at 1520.2 nm. Our scheme provides a compact and high performance frequency reference in the communication band.     

Tunable single and multiwavelength continuous-wave c-cut Nd:YVO4 laser

We report a discretely tunable, single and multiwavelength continuous-wave diode-end-pumped laser with a c-cut Nd:YVO₄ crystal lasing on the ⁴F_3/2?C⁴I_11/2 intermanifold transitions and an intracavity sub-THz free-spectral-range etalon. Experimental results show that it is tunable in the discrete regions of 1066.5?C1066.8, 1083.1?C1084.6, and 1087.2?C1088.2?nm and operates simultaneously at dual-wavelengths of (1084.6, 1087.4), (1066.5, 1088.0), (1066.8, 1083.3) nm by changing the angle of an intracavity etalon with 0.67 THz free-spectral range. With a proper etalon angle, the laser can also simultaneously oscillate at four wavelengths of 1066.9, 1082.9, 1085.7, and 1088.3?nm with a total output power of 1.2?W at an incident diode pump power of 15?W. Similar performance of the laser at different wavelengths was also achieved by using a 0.88?THz free-spectral-range etalon in the same laser cavity.     

Generation of tunable far-infrared radiation with a quantum cascade laser

We demonstrate the generation of cw tunable far-infrared radiation by mixing a quantum cascade laser and a CO>(2) laser in a W-Ni metal-insulator-metal diode. The first known spectroscopic application to the recording of an H(79)Br transition near 4.47 THz is reported.     

Efficiency intracavity frequency-doubled Nd:CNGG-LBO green laser at 530.5 nm under direct 885 nm pumping into the emitting level

We report an efficient laser emission on the 1061 nm ⁴ F _3/2 to ⁴ I _11/2 transition in Nd:CNGG under the pump with diode laser at 885 nm. Continuous wave (CW) 5.4 W output power at 1061 nm is obtained under 17.4 W of incident pump power; the slope efficiency with respect to the incident pump power was 36.2%. Moreover, intracavity frequency doubling with LiB₃O₅ (LBO) nonlinear crystal yielded 1.75 W of green light at 530.5 nm. An optical-to-optical efficiency with respect to the incident pump power was 10.1%.     

CW red light generated by intracavity frequency doubling of a 1329 nm Nd:CNGG laser with LBO

We report an efficient laser emission on the 1329 nm ⁴ F _3/2 to ⁴ I _13/2 transition in Nd:CNGG under the pump with diode laser at 885 nm. Continuous wave (CW) 3.37 W output power at 1329 nm is obtained under 17.4 W of incident pump power; the slope efficiency with respect to the incident pump power was 36.2%. Moreover, intracavity frequency doubling with LiB₃O₅ (LBO) nonlinear crystal yielded 822 mW of red light at 665 nm. An optical-to-optical efficiency with respect to the incident pump power was 4.7%.     

Simulation of THz emission from laser interaction with plasmas

One-dimensional particle-in-cell (PIC) program is used to simulate the generation of high power terahertz (THz) emission from the interaction of an ultrashort intense laser pulse with underdense plasma. The spectra of THz radiation are discussed under different laser intensity, pulse width, incident angle and density scale length. High-amplitude electron plasma wave driven by a laser wakefield can produce powerful THz emission through linear mode conversion under certain conditions. With incident laser intensity of 10¹⁸ W/cm², the generated emission is computed to be of the order of several MV/cm field and tens of MW level power. The corresponding energy conversion efficiency is several ten thousandths, which is higher then the efficiency of other THz source and suitable for the studies of THz nonlinear physics.     

Generation of sum-frequency sideband using 964 GHz HCN laser and 70 GHz klystron radiation

Continuosly tunable submillimeter radiation above 1 THz has been generated by sum-frequency mixing of HCN laser radiation (second strongest transition at 964.3 GHz) with that of klystron (70 GHz) in the Schottky barrier diode used as the non-linear element. Generated radiation was sufficiently strong to allow the high resolution frequency measurement of 9_9,1 8_8,0 transition in³²S¹⁶O.     

Diode-pumped continuous-wave Nd:YLF laser at 1313 nm

We present an efficiency Nd:LiYF₄ (Nd:YLF) laser operating at 1313 nm pumped directly into the emitting level ⁴ F _3/2. At the incident pump power of 10.3 W, as high as 3.1 W of continuous-wave output power at 1313 nm is achieved. The slope efficiency with respect to the incident pump power was 36.1%. To the best of our knowledge, this is the first demonstration of such a laser system. Comparative results obtained for the pump with diode laser at 806 nm, into the highly absorbing ⁴ F _5/2 level, are given in order to prove the advantages of the 880 nm wavelength pumping.     

All-solid-state CW Nd:LuVO<Subscript>4</Subscript>-LBO laser at 533 nm under direct 888 nm pumping

We report an efficient laser emission on the 1066 nm ⁴ F _3/2 to ⁴ I _11/2 transition in Nd:LuVO₄ under the pump with diode laser at 888 nm. Continuous wave (CW) 11.2 W output power at 1066 nm is obtained under 18.3 W of incident pump power; the slope efficiency with respect to the incident pump power was 71.9%. Moreover, intracavity frequency doubling with LiB₃O₅ (LBO) nonlinear crystal yielded 4.2 W of green light at 533 nm. An optical-to-optical efficiency with respect to the incident pump power was 23.0%.     

Intracavity optical parametric oscillator pumped by an actively Q-switched Nd:YAG laser

A non-critically phase-matched KTiOPO₄ optical parametric oscillator (OPO) intracavity pumped by a laser diode end-pumped acousto-optically Q-switchedNd:YAG laser is experimentally demonstrated. The highest average power is obtained at the pulse repetition rate (PRR) of around 15 kHz, which is different from the widely reported Nd:YVO₄ laser pumped OPO in which the highest average power is obtained at a very high PRR, e.g. 80 kHz. With an incident laser diode power of 6.93 W and a pulse repetition rate of 15 kHz, an average signal power of 0.72 W is obtained with a peak power of 7.7 kW and an optical-to-optical conversion efficiency of 10.4%. PACS 42.65.Yj; 42.60.Gd; 42.55.Xi     

Continuous-wave diode-pumped operation of an Yb:NaLa(WO4)2 laser at room temperature

Room-temperature continuous-wave (cw) laser operation is demonstrated with the newly developed Yb:NaLa(WO₄)₂ disordered crystal by end-pumping with a fiber-coupled diode laser. A maximum output power of 330 mW is obtained with an optical efficiency of 4.9% and a slope efficiency of 6.3% with respect to the incident pump power. The efficiencies in terms of the absorbed pump power are roughly three times higher. Sellmeier dispersion curves for the ordinary and extraordinary refractive indices of the NaLa(WO₄)₂ host are reported along with crystallographic and spectroscopic properties related to the Yb³⁺-doping.     

Generation of THz Radiation from Laser Beam Filamentation in a Magnetized Plasma

The terahertz (THz) frequency radiation production as a result of nonlinear interaction of high intense laser beam with low density ripple in a magnetized plasma has been studied. If the appropriate phase matching conditions are satisfied and the frequency of the ripple is appropriate then this difference frequency can be brought in the THz range. Self focusing (filamentation) of a circularly polarized beam propagating along the direction of static magnetic field in plasma is first investigated within extended‐paraxial ray approximation. The beam gets focused when the initial power of the laser beam is greater than its critical power. Resulting localized beam couples with the pre‐existing density ripple to produce a nonlinear current driving the THz radiation. By changing the strength of the magnetic field, one can enhance or suppress the THz emission. The expressions for the laser beam width parameter, the electric field vector of the THz wave have been obtained. For typical laser beam and plasma parameters with the incident laser intensity ≈ 10¹⁴ W/cm², laser beam radius (r₀) = 50 μm, laser frequency (ω₀) = 1.8848 × 10¹⁴rad/s, electron plasma (low density rippled) wave frequency (ω₀) = 1.2848 × 10¹⁴ rad/s, plasma density (n₀) = 5.025 × 10¹⁷cm^–3, normalized ripple density amplitude (μ)=0.1, the produced THz emission can be at the level of Giga watt (GW) in power (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Efficiency intracavity frequency-doubled Nd:Y<Subscript>0.36</Subscript>Gd<Subscript>0.64</Subscript>VO<Subscript>4</Subscript>-LBO green laser at 532 nm with direct pumping

We report an efficient laser emission on the 1064 nm ⁴ F _3/2 to ⁴ I _11/2 transition in mixed vanadate crystal Nd:Y_0.36Gd_0.64VO₄ under the pump with diode laser at 880 nm. Continuous wave (CW) 10.7 W output power at 1064 nm is obtained under 17.8 W of incident pump power; the slope efficiency with respect to the incident pump power was 71.2%. Moreover, intracavity frequency doubling with LiB₃O₅ (LBO) nonlinear crystal yielded 4.6 W of green light at 532 nm. An optical-to-optical efficiency with respect to the incident pump power was 25.8%.     

Mixing of 30 THz laser radiation with nanometer thin-film Ni-NiO-Ni diodes and integrated bow-tie antennas

Mixing experiments with 30 THz CO₂-laser radiation as well as the detection of 35 ps 30 THz pulses of an optical-free-induction-decay CO₂-laser system have been performed with the first nanometer thin-film Ni-NiO-Ni diodes with a minimum contact area of 0.012 µm². Difference frequencies up to 85 MHz were detected by mixing two different CO₂-laser beams coupled to the diode with an integrated bow-tie antenna. The dependence of the beat signal on bias voltage, laser power and polarization of the infrared laser radiation was determined.     

Efficient CW Nd:GdVO<Subscript>4</Subscript>-BiBO deep-blue laser at 456 nm under direct 888 nm diode laser pumping

We report an efficient laser emission on the 912 nm ⁴ F _3/2 to ⁴ I _9/2 transition in Nd:GdVO₄ under the pump with diode lasers at 888 nm. Continuous wave (CW) 4.91 W output power at 912 nm is obtained under 18.3 W of incident pump power; the slope efficiency with respect to the incident pump power was 57.5%. Moreover, intracavity frequency doubling with BiB₃O₆ (BiBO) nonlinear crystal yielded 1.33 W of deep-blue light at 456 nm.     

Efficient intracavity frequency-doubled Nd:GdVO4-LBO red laser at 670.5 nm under direct 888 nm pumping

We report an efficient laser emission on the 1341 nm ⁴ F _3/2 to ⁴ I _13/2 transition in Nd:GdVO₄ under the pump with diode lasers at 888 nm. Continuous wave (CW) 6.58 W output power at 1341 nm is obtained under 18.3 W of incident pump power; the slope efficiency with respect to the incident pump power was 45.1%. Moreover, intracavity frequency doubling with LiB₃O₅ (LBO) nonlinear crystal yielded 1.77 W of red light at 670.5 nm.     

Efficient diode-pumped Nd:GGG laser operation at 933.6 and 937.3 nm

CW laser emission on the quasi 3-level (⁴F_3/2→⁴I_9/2) transition in Nd:GGG is reported for different pump focusing and resonator dimensions. A nearly hemispherical plano-concave resonator led at 937.3 nm to a maximum output power of 4.1 W for an incident pump power of 21.7 W, thus corresponding to a slope efficiency of about 23.5%. Laser operation was also obtained for the first time around 933.6 nm by using a glass etalon for frequency selection with a maximum output power of 2.3 W and a slope efficiency of 16% with respect to the incident pump power. Dual-wavelength operation (around 933.6 and 937.3 nm), which offers a potential source to generate THz radiation, is also reported.     

Efficient Nd:Y0.5Gd0.5VO4-KTiOPO4 green laser under diode pumping into the emitting level 4F3/2

We report a green laser at 532 nm generation by intracavity frequency doubling of a continuous wave (cw) laser operation of a 1064 nm Nd:Y_0.5Gd_0.5VO₄ laser under diode pumping into the emitting level ⁴ F _3/2. A KTiOPO₄ (KTP) crystal, cut for critical type-II phase matching at room temperature is used for second harmonic generation (SHG) of the laser. At an incident pump power of 17.8 W, as high as 4.21 W of cw output power at 532 nm is achieved. The optical-to-optical conversion efficiency is up to 23.6%, and the fluctuation of the green output power was better than 2.8% in the given 30 min.     

Frequency measurement of the 496 μm line of a CH3F FIR laser

A direct frequency measurement of the 496 μm, K = 2 line from a CH₃F laser is reported. Our laser is a metallic wave-guide device pumped by a frequency stabilized CO₂ laser; its output is mixed in a CaAs-Au Schottky barrier diode with a 100 GHz klystron and the beat note is observed on a spectrum analyzer. The result is f_CH3F(496 μm, K = 2) = 604 297.5 ± 0.2 MHz.     

THz radiation generation via the interaction of two‐colour ultra‐short laser pulses with SO2 and NH3 gases

In this work, using a two‐dimensional particle‐in‐cell Monte Carlo collision computation method, terahertz (THz) radiation generation via the interaction of two‐colour, ultra‐short, high‐power laser pulses with the polyatomic molecular gases sulphur dioxide (SO₂) and ammonia (NH₃) is examined. The influence of SO₂ and NH₃ pressures and two‐colour laser pulse parameters, i.e., pulse shape, pulse duration, and beam waist, on the THz radiation generation is studied. It is shown that the THz signal generation from SO₂ and NH₃ increases with the background gas pressure. It is seen that the THz emission intensity for both gases at higher laser pulse durations is higher. Moreover, for these polyatomic gases, the plasma current density increases with increase in the laser pulse beam waist. A more powerful THz radiation intensity with a larger time to peak of the plasma current density is observed for SO₂ compared to NH₃. In addition, many THz signals with small intensities are observed for both polyatomic gases. It is seen that for both SO₂ and NH₃ the generated THz spectral intensity is higher at higher gas pressures.