N2 laser frequency conversion by stimulated Raman scattering in H2

High-efficiency frequency conversion in H₂ of a nitrogen laser oscillator-amplifier system is described. The laser system provides about 1 MW output power with a very low intrinsic divergence. Up to 3 Stokes lines at 392, 468, and 581 nm and 3 Anti-Stokes at 296, 263, and 237 nm, respectively, have been observed at the output of the 60 cm long H₂ Raman cell. Peak power values of 500, 300, and 70 kW have been measured for the first 3 Stokes, respectively, corresponding to a 56% pump energy conversion efficiency.A comparison between free and guided propagation (in a hollow dielectric waveguide) is also reported, for various values of the pump intrinsic divergence.     

Tunable infrared generation using third Stokes output from a waveguide Raman shifter

Tunable infrared output has been produced by stimulated Raman scattering of visible dye laser radiation in hydrogen gas using a capillary waveguide to enhance conversion to the third Stokes (S₃). With 568 nm pumping an output energy of 2 mJ is observed near 2 μ m, representing a 4% energy conversion efficiency into S₃). Higher wavelengths yield much lower energies (0.5 mJ at 3 μ m and 0.02 mJ at 4.55 μ m), reflecting the observed dependence of third Stokes output on the inverse of the fifth power of the generated wavelength.     

Tapered waveguide semiconductor raman laser

Semiconductor Raman laser can act as a heterodyne demodulator of terahertz-band modulated light wave signals in wideband optical communication systems. We have been developing the semiconductor Raman laser with a waveguide structure composed of a GaP core and Al_xGa_1–xP cladding layers. The tapered waveguide structure can reduce the threshold pump power by increasing the internal pump power density. Fabricated tapered waveguide semiconductor Raman laser have shown the threshold pump power of 160 mW. Discussion is made on the origin of losses as well as the limit of the low pump power operation.     

Output power and intracavity intensity profiles of a quasi-continuous end-pumped Nd:YVO4 self-Raman mini laser

The paper presents experimental investigation and modeling of an end-pumped quasi-continuous-wave YVO₄/Nd:YVO₄ mini self-Raman laser. The dependence of the Stokes output power on the pump power in the range from 3 to 17.5 W has been measured. As much as 1.76 W of an average Stokes power, corresponding to a total optical-to-optical conversion efficiency of about 10%, has been obtained. The transverse profiles of the laser (at the fundamental wavelength) and the Stokes beam intensity have been recorded at the output mirror and in the vicinity of the boundary between the pure and Nd-doped parts of the Raman crystal. These distributions have been approximated by the sum of Gaussian and super-Gaussian distributions with corresponding weights. We propose a model of such lasers that takes into account the features of intracavity self-frequency Raman conversion in lasers with highly inhomogeneous non-Gaussian spatial distributions of the pump, laser, and Stokes beam intensity in the cavity. The results of modeling are in good agreement with the experimental data.     

Simultaneous intracavity optical parametric oscillation and stimulated Raman scattering pumped by a doubly passively Q-switched Nd:GGG laser

By using a doubly passively Q-switched Nd:Gd₃Ga₅O₁₂(Nd:GGG) laser with Cr⁴⁺:YAG and GaAs as saturable absorbers as pump laser, simultaneous intracavity optical parametric oscillation and stimulated Raman scattering based on a single X-cut KTiOPO₄ (KTP) crystal have been realized. Under an incident diode pump power of 10.5 W, the output powers at the signal wave near 1,569 nm and the first Stokes emission near 1,094 nm were 218 and 72 mW, corresponding to the optical-to-optical conversion efficiencies of 2.08 and 0.69 %, respectively. The measured shortest pulse duration at the signal wave near 1,569 nm was 580 ps, generating a pulse peak power of 43.7 kW, while the minimum pulse duration at the first Stokes emission near 1,094 nm was 1.61 ns. By adjusting the tilt angle of the KTP crystal, up to the third Stokes scattering was also obtained.     

An efficient,RF excited,waveguide CO2 laser

A CW waveguide CO₂ laser excited by a transverse radiofrequency discharge is described. An efficiency of 8.5% (laser power/RF power from supply) has been achieved and an output power of up to 4.6 W.     

Intracavity Raman laser generating a third stokes component at 1.5 μm

The lasing properties of an intracavity Nd:KGW Raman laser which converts the multimode radiation of an Nd:KGW laser operating on the ⁴ F _3/2–⁴ I _11/2 transition into the third Stokes component at a wavelength of 1.5 μm are studied. The energy in the third Stokes component is found to increase essentially linearly with the electrical energy delivered to the flashlamp. Lasing at the third Stokes component begins in the central portion of the Nd:KGW crystal and then propagates to its boundaries. Reducing the geometric aperture of the multimode pump beam in the Raman crystal lowers the divergence of the Stokes emission. For a source pump energy of 6 J, the intracavity Raman laser emits 14.7 mJ pulses of duration 3–4 nsec which are safe to the eyes. The divergence of the Raman laser beam at a level of 86% of the total energy is ≈ 9 mrad.     

Anti-stokes fluorescence of polymethine dyes excited by a titanium-sapphire laser

Fluorescence of symmetric polymethine dye solutions (λ _abs ^max ≈ 700 nm) upon anti-Stokes excitation by cw radiation of a titanium-sapphire laser (781 nm) is first investigated. A series of six compounds with analogous composition and spectral and luminescent properties is investigated. It is demonstrated that in addition to the anti-Stokes component, the Stokes component with a maximum at 820 nm (referred to the H-aggregates of initial dyes) is observed in the fluorescence spectra of solutions of the examined molecules when dye concentration increases to 10⁻³ M. Dependences of the anti-Stokes and Stokes component intensities on the exciting radiation power are obtained that confirm a linear excitation character. On examples of xanthene and polymethine dyes, the use of organic fluorophors for anti-Stokes laser cooling and some other possible applications of the anti-Stokes fluorescence are discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 63–70, March, 2007.     

Coupled-cavity passively Q-switched two-Stokes microchip laser

Experimental and theoretical studies of the coupled-cavity diode-pumped Nd:YAG/Cr:YAG microchip lasers with intracavity Raman conversion of laser pulses in a Ba(NO₃)₂ crystal into two Stokes pulses have been made. Two lasers with a different cavity length have been investigated. The minimal pulse durations at the 2nd Stokes wavelength were ??100 ps in the short-cavity laser at pulse energy of 5???J, and the pulse repetition rate reached 20?C24?kHz. The laser and Stokes pulse dynamics, as well as the spatial intensity distribution of the laser and the 1st Stokes beams at the output mirror have been recorded. A model describing such coupled-cavity microchip Raman lasers has been developed. The numerically simulated laser and Stokes pulse dynamics, and the calculated pulse energy, duration, and repetition rate are in good agreement with the experimental data.     

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.     

CO2 laser drives extreme ultraviolet nano-lithography — second life of mature laser technology

It was shown both theoretically and experimentally that nanosecond order laser pulses at 10.6 micron wavelength were superior for driving the Sn plasma extreme ultraviolet (EUV) source for nano-lithography for the reasons of higher conversion efficiency, lower production of debris and higher average power levels obtainable in CO₂ media without serious problems of beam distortions and nonlinear effects occurring in competing solid-state lasers at high intensities. The renewed interest in such pulse format, wavelength, repetition rates in excess of 50 kHz and average power levels in excess of 18 kiloWatt has sparked new opportunities for a matured multi-kiloWatt CO₂ laser technology. The power demand of EUV source could be only satisfied by a Master-Oscillator-Power-Amplifier system configuration, leading to a development of a new type of hybrid pulsed CO₂ laser employing a whole spectrum of CO₂ technology, such as fast flow systems and diffusion-cooled planar waveguide lasers, and relatively recent quantum cascade lasers. In this paper we review briefly the history of relevant pulsed CO₂ laser technology and the requirements for multi-kiloWatt CO₂ laser, intended for the laser-produced plasma EUV source, and present our recent advances, such as novel solid-state seeded master oscillator and efficient multi-pass amplifiers built on planar waveguide CO₂ lasers.     

A DC excited waveguide multibeam CO2 laser using high frequency pre-ionization technique

High power industrial multibeam CO₂ lasers consist of a large number of closely packed parallel glass discharge tubes sharing a common plane parallel resonator. Every discharge tube forms an independent resonator. When discharge tubes of smaller diameter are used and the Fresnel numberN ≪ 1 for all resonators, they operate in waveguide mode. Waveguide modes have excellent discrimination of higher order modes. A DC excited waveguide multibeam CO₂ laser is reported having six glass discharge tubes. Simultaneous excitation of DC discharge in all sections is achieved by producing pre-ionization using an auxiliary high frequency pulsed discharge along with its other advantages. Maximum 170 W output power is obtained with all beams operating in EH₁₁ waveguide mode. The specific power of 28 W/m is much higher as compared to similar AC excited waveguide multibeam CO₂ lasers. Theoretical analysis shows that all resonators of this laser will support only EH₁₁ mode. This laser is successfully used for woodcutting     

Measurement of rotational temperature in CO2 waveguide laser medium

A small-signal gain in CO₂ waveguide laser medium has been measured on rotational-vibrational transitions in the P-branch of the (0, 0, 1)-(0, 2⁰, 0) band. It has been found that the rotational temperature is well defined in the waveguide laser system where high excitation power is injected and a large amount of energy is flowing through vibrational, rotational, and translational degrees of freedom. The rotational temperature is slightly higher than the translational temperature.     

The generation of high pulse and average power radiation in eye-safe spectral region by the third stokes generation in barium nitrate Raman laser

The generation of high pulse and average power radiation in the eye-safe region (wavelength around 1.599 μm) by the third Stokes generation in a barium nitrate Raman laser was demonstrated by pumping with 10 ns pulses of a Nd:YAG laser. Converted pulse energy was up to 93 mJ (peak power was 10 MW) at a pump energy of 300 mJ, which corresponds to a quantum efficiency of 47%. The average output power of the third Stokes radiation was 1.8 W.     

Diode-pumped continuous-wave Nd:YVO<Subscript>4</Subscript> laser with self-frequency Raman conversion

Continuous-wave operation of a diode-pumped Nd:YVO₄ laser with self-frequency Raman conversion is demonstrated. The threshold of Raman generation was measured to be 1.3 W of laser diode power. The maximum output power of Stokes radiation at the wavelength of 1177 nm was up to 50 mW at a laser diode pump power of 2.3 W, corresponding to the slope efficiency of 5%. The beam quality M² of the Stokes radiation was about 1.4. The fluctuations of the Stokes power were minimised down to 4%. PACS 42.55.Ye; 42.60.Pk; 42.65.Dr     

A high power, 1.22 mm 13C H3 laser

Pulsed power levels in excess of 5 kW at wavelengths near 1.2 mm have been obtained via optical pumping of ¹³C H₃F in a 3 m, mirrorless waveguide laser, using a CO₂ TEA laser as a source of pump radiation.     

Quartz CO2 waveguide laser with a separated diffraction grating

A quartz CO₂ waveguide laser with external totally reflecting mirrors and a NaCl plate for the output power coupling is described. The output power was measured as a function of the distance of the mirrors from the waveguide aperture. Using a diffraction grating instead of one of the mirrors the output power at the 10 P(20) line was measured as a function of the mirror position. The results sustain the assumption of a multimode waveguide structure.     

Mechanism and process of fabricating fluorinated polyimide optical waveguide by CO2 laser direct-writing

Fluorinated polyimide waveguides were fabricated by CO₂ laser direct-writing. The poly(amic acid) micro-region irradiated by CO₂ laser beam was studied with FT-IR micro-spectroscopy. The FT-IR spectra implied that the laser induced thermal-imidized polyimide was of optical anisotropy, and the imidization degree of exposed micro-region increased with the rising of output laser power. The increased aspect ratio of waveguide and smoothness of surface can be achieved by increasing the pre-cured temperature (below 120°C) and writing speed, and optimizing laser power and the distance between the lens and the annular aperture. The guided light was clearly confined to the core of the fabricated waveguide, which means this technique can be used for fluorinated polyimide waveguide fabrication.     

Manufacturing of Nd:Gd3Ga5O12 ridge waveguide lasers by pulsed laser deposition and ultrafast laser micromachining

Laser radiation is used both for the deposition of the laser active thin films and for the micro structuring to define wave guiding structures for the fabrication of waveguide lasers. Thin films of crystalline and amorphous neodymium doped Gd₃Ga₅O₁₂ are grown on single crystal yttrium aluminium garnet by pulsed laser deposition using excimer laser radiation.Manufacturing of the laser active waveguides by micro structuring is done using femtosecond laser ablation of the deposited films. The structural and optical properties of the films and the morphology of the structured waveguides are determined in view of the design and the fabrication of compact and efficient diode pumped waveguide lasers. The resulting waveguides are polished, provided with resonator mirrors, pumped using diode lasers and the waveguide lasers are characterized. The spectroscopic properties of the amorphous waveguide are investigated and an infrared waveguide laser is demonstrated. To our knowledge, there have been no reports by other groups of the successful operation of a structured waveguide laser fabricated by this technique or of a waveguide laser made from amorphous neodymium doped Gd₃Ga₅O₁₂.     

高功率、高效率808nm半导体激光器阵列

通过设计高效率808 nm非对称宽波导外延结构,减少P型波导层和包层的自由载流子光吸收,实现腔内光吸收损耗为0.63 cm~(-1).制备的808 nm半导体激光器阵列在室温25?C下,实现驱动电流135 A,工作电压1.76 V,连续输出功率大于150 W,斜率效率高达1.25 W/A,中心波长809.3 nm,器件最高电光转换效率为65.5%,这是目前国内报道的808 nm半导体激光器阵列的最高电光转换效率,达到国际同类器件最好水平.