Electron beam excitation studies of potential dye vapor phase laser systems

Excitation processes of selected dye vapor-rare gas mixtures pumped by an electron beam have been studied. These experiments revealed the importance of effective collisional electron energy transfer pumping via a dense rare gas rather than a radiative energy transfer from an excimer laser gas mixture to achieve population inversion in an organic dye vapor. Work supported in part by the Energy Research and Development Adinistration, the Robert A. Welch Foundation and the National Science Foundation.     

A single-mode KrF laser

Single-mode operation of a KrF laser oscillator has been achieved for the first time. The laser medium is pumped by an electron beam which allows excitation for a much longer duration than with discharge pumping. The long excitation time, together with the use of a short oscillator cavity with a low single-pass gain, allows many roundtrips before saturation is reached. This makes line-narrowing easier and single-mode operation has been achieved using only two intracavity etalons.Technical Research Centre of Finland, Helsinki, Finland     

Solid-state laser passively Q-switched in a new geometry

A new passive Q-switching geometry of a laser cavity has been proposed. In the proposed scheme, the volume of the passive Q-switch just partially overlaps the intracavity laser beam cross-section, leading, however, to the entire beam modulation. This technique was applied for passive Q-switching of a flash-lamp pumped multimode YAG:Nd³⁺ laser by LiF:F₂⁻ crystals. The giant pulse laser action threshold has been detected in the proposed geometry, and is lower than that in the scheme where the passive Q-switch operates in the traditional manner. Stable giant pulse oscillation of 1064 nm wavelength with a pulse duration of 24 ns, pulse energy of 450 mJ, and pulse repetition rates of up to 100 Hz, have been obtained.     

Influence of spatial mode matching in end-pumped solid state lasers

We present investigations on the influence of mode matching on the efficiency of longitudinally pumped solid state lasers. In a theoretical part we enhance an existing model for four level lasers from idealized cylindrical modes to arbitary pump and laser modes in a random relative position thereby neglecting beam deformation due to thermal effects. The theoretical predictions were confirmed experimentally with an end-pumped Nd:YAG rod operated at 1064 nm. To investigate the effect of misalignment on the efficiency we used a Ti-Sapphire pump laser which was displaced relative to the laser beam. To establish the influence of arbitary pump modes on laser performance a diode laser equipped with coupling optics served as pump source for the same resonator. The resulting decrease in slope efficiency compared to the Ti-Sapphire pumped system could be explained in terms of limited mode overlap due to the characteristic pump field distribution produced by the diode coupling optics.     

LD end pumped, actively mode locked and passively Q-switched Nd:YAP laser at 1341 nm

An end pumped Nd:YAP laser at 1341 nm is actively mode locked and passively Q-switched. Pumping was done with a pulsed high power laser diode with maximum power 425 W. V³⁺:YAG with 61% initial transmission served as saturable absorber, and an acousto-optic modulator is used for active mode locking. The output pulse train with 69 ns duration has a total energy of 3.2 mJ with ±4% shot-to-shot fluctuation. The peak output energy of a single mode locked pulse is 0.25 mJ. The pulse duration of a single mode locked pulse is less than 800 ps. The output laser beam is nearly diffraction limited with 1.6 mm diameter, and beam propagation factor M² about 1.3.     

Transversely pumped laser using F 3 + and F2 mixed color centers in a LiF crystal at room temperature

A stable laser with F₃⁺ and F₂ mixed color centers in LiF crystal is constructed using a transversely pumped cavity at room temperature. The mixed color center laser is pumped with a nitrogen-laser-pumped dye laser. A pulse output of the laser is 0.23 mJ. The pulse widths of the F₃⁺ and F₂ color center lasers are about 12 and 8.5 ns, respectively. The optical–optical conversion efficiency is about 5.0%. The divergence of the F₃⁺ color center laser beam is about 2.2 mrad and that of the F₂ color center laser beam about 3.5 mrad. The polarization of the mixed color center laser is about 0.97. The output of the F₃⁺ color center laser extends from 515 to 575 nm and peaks at 540 nm, while that of the F₂ color center laser extends from 633 to 705 nm and peaks at 667 nm.     

Three-Rod Resonator for Krypton Lamp Pumped 1.8 kW Continuous-Wave Nd：YAG Laser

A three-rod series resonator cw Nd:YAG laser suitable for the industrial applications is presented. The symmetrical resonator laser has been developed and is rated at 1820-W output power with beam parameter product 24 mm.mrad. By utilizing the symmetrical resonator design, the characteristic of beam with multi-rod is not obviously decreased compared with that of a single one. The system total electro-optics efficiency of lamp pumped YAG crystal is as high as 4.0%. The main factors, which affect output power and beam quality of high power solid-state laser module, are theoretically analysed.     

High peak power Nd:YAG laser pumped by 600-W diode laser stack

The Q-switched laser with triangle slab made of Nd:YAG crystal side pumped by 600-W quasi-cw diode laser stack has been designed. The multimode (M²≈2.6) output energy of about 42 mJ was demonstrated in free running mode for110-mJ pump energy. In Q-switch experiments, the KDDP Pockels cell was placed between the slab and rear mirror in plane-plane cavity with output coupler of 84% transmission. The energy of 8 mJ in 2.1-ns pulse duration was obtained for near TEM₀₀ output beam. For passive Q-switching by means of Cr:YAG crystal of 12.6% unsaturated transmission, the energy of 5.1 mJ in 2.5-ns pulse duration was obtained for output beam close to TEM₀₀ mode.     

Femtosecond 5-W Yb:KGW slab laser oscillator pumped by a single broad-area diode and its application as supercontinuum source

We demonstrate a novel and very simple design for an efficient high-power femtosecond Yb:KGW slab laser oscillator. The laser is capable of producing output powers of more than 5 W at 44-MHz repetition rate and pulse widths as short as 161 fs with a nearly diffraction limited beam and an optical-to-optical efficiency of more than 28%. The laser is pumped by a single broad-area laser diode and employs simple pump optics consisting of three lenses. The laser output power is distributed between two beams and single or combined outputs are discussed. In combination with a tapered fiber the laser was used to generate femtosecond supercontinua with up to 1.3-W average power and spectra spanning from 420 to over 1750 nm.     

Continuous-wave high-power multi-pass pumped thin-disc Nd:GdVO4 laser

A thin-disc Nd:GdVO₄ laser in multi-pass pumping scheme was developed. Continuous-wave output power of 13.9 W at 1.06 μm for an absorbed power at 808 nm of 22 W was demonstrated from a 250-μm thick, 0.5-at.% Nd:GdVO₄ in a 4-pass pumping; the slope efficiency in absorbed power was 0.65, or 0.47 in input power. Output performances were also investigated under diode laser pumping at 879 nm, directly into the emitting ⁴F_3/2 level: maximum power of 3.6 W was obtained at 6.2 W of absorbed power with 0.69 slope efficiency. Compared with pumping at 808 nm, into the highly absorbing ⁴F_5/2 level, improvements of laser parameter in absorbed power (increase of slope efficiency, decrease of threshold) were obtained, showing the advantages of the pumping into the emitting level. However, the laser performances expressed vs. the incident power were modest owing to the low absorption efficiency at 879 nm. Thus, increased number of passes of the medium would be necessary in order to match the performances in input power obtained under 808-nm pumping.     

A Compact All-Solid-State 630-ps 9.43-kHz High Power Nd：YAG/Nd：YVO4 Hybrid Laser System

We present a simple and compact design for an all-solid-state laser amplifier system which can output 9.43-kHz 630-ps, 3.5-W pulse trains under 20 W absorbed pumping power. The excellent matching between the repetition of its seed source and the fluorescence lifetime of the amplifying medium makes it quiet efficient for the four-pass amplifier to be pumped in cw mode without need of any synchronization device between the oscillator and the amplifier. The entire setup just covers an area of 55 × 25 cm^2. The output average power fluctuation is less than ±1.5% within 10min and 3% within 6h.     

Solid-state active media of tunable organic- compound lasers pumped with a laser. II. A copper vapor laser

The lasing properties of organic compounds in a polymethylmethacrylate matrix pumped by a copper vapor laser are studied. The results demonstrate that the transverse pumping scheme of solid-state laser-active media with the copper vapor laser is promising compared to the longitudinal pumping scheme from the viewpoint of the lifetime parameters. Received: 6 February 2002 / Published online: 2 May 2002     

A diode-pumped, frequency-doubled, tunable single-mode quasi-continuous-wave Yb:YAG laser emitting 70 W peak power at 515 nm

An efficient pumping scheme for a quasi-continuous-wave diode-pumped Yb:YAG laser is presented. Single-mode operation and fine wavelength tuning are assured by the use of a rubidium titanyl phosphate (RTP) Fabry–Perot étalon. When frequency doubled, the 200–420 μs duration pulses reach a peak power of 70 W at a wavelength of 515 nm. The TEM₀₀ beam is nearly diffraction limited with an M ² factor of 1.06 at full power. The tuning range spans from 512 to 520 nm and the pulse to pulse frequency stability is on the order of ±10 MHz. Laboratoire Aimé Cotton is associated with Université Paris Sud 11.     

Application of the opto-acoustic effect to the operation of optically pumped far-infrared gas lasers

A method is reported which allows the operation of optically pumped farinfrared (FIR) gas lasers in a simple way: A spectrophone is used to control and to stabilize the pump laser frequency in order to achieve most efficient optical pumping of the FIR laser gas.     

Temporal extension of stable glow discharges in fluorine-based excimer laser gas mixtures by the addition of xenon

The effect of addition of xenon on the long term homogeneity of discharges in F₂and ArF excimer laser gas mixtures was investigated in a small-volume discharge chamber. The gas mixture in the discharge chamber was preionized by X-rays. A special electrical excitation circuit containing a pulse forming line provided a long, square-shaped current pumping pulse of a predetermined duration to the discharge electrodes. The initiation and the development of the discharge was monitored via its fluorescence signal with an intensified CCD camera. We found that adding Xe up to partial pressures of 0.53 mbar extended the homogeneous phase of the discharge from 80 ns to approximately 200 ns in He/F₂as well as in He/Ar/F₂and Ne/Ar/F₂excimer laser gas mixtures. Monitoring of the ArF and XeF spontaneous emission signals showed that the formation of ArF excimers remained unaffected by the addition of xenon (up to 1.3 mbar) to the laser gas mixture.     

A pulsed dye laser with grazing incidence and folded cavity

A novel design of a transversally pumped pulsed dye laser resonator using grazing incidence in a folded astigmatic cavity is described. The stability conditions, beam waist and output divergence of the oscillating mode are derived from the ray transfer matrix for this cavity. A diffraction limited gaussian beam is obtained. The linewidth can be adjusted down to 610 MHz without using any intracavity etalon.     

AOM fourfold pass for efficient Q-switching and stable high peak power laser pulses

We report on a scheme for efficient acousto-optical Q-switching. A flash lamp pumped Nd:YAG oscillator with an acousto-optic modulator (AOM) fourfold pass configuration is presented. The setup combines two important advantages: enhancement of the diffraction efficiency by additional AOM passes and a compact oscillator design in spite of an extension of the optical path length. A flash lamp pumped oscillator with an average output power of 7 W and a beam quality of M² = 1.2 is developed. The system operates with a 100 Hz repetition rate for the flash lamps. In each pumping pulse a pulse train of 1 up to 40 Q-switched laser pulses is generated. The pulse duration is from 15 to 120 ns. In comparison to a former setup (AOM double pass) the AOM fourfold pass configuration allows single pulses with energy above 20 mJ and a pulse peak power of more than 1 MW. In addition, the beam profile is improved due to a better separation of the incident and diffracted beam caused by the AOM. The laser is dedicated as master oscillator in a master oscillator power amplifier (MOPA) system where pulse peak powers in the MW range should be achieved.     

Efficient fourth harmonic UV generation of passively Q-switched Nd:GdVO4/Cr:YAG lasers

A coherent UV passively Q-switched diode pumped Nd:GdVO₄ laser source is proposed. During pumping of the β-BBO crystal a stable light with power 0.6 W with wavelength 532 nm and pulse duration 9 ns at frequency repetition 16 kHz was applied. The output UV light has a power about 79 mW at wavelength 266 nm during diode-pumping with 8 W incident light.     

Dual-frequency optical pumping for spin-polarizing a lithium atomic beam

A lithium-6 atomic beam is spin-polarized by means of optical pumping with a single-mode dye laser operating on the resonance transition. Simultaneous pumping of both hyperfine substates is achieved by frequency-splitting the laser light with an acousto-optic modulator. A polarization dependent signal, obtained by probing the optical activity of the beam with linearly polarized light, is utilized in a microprocessor-controlled laser stabilization scheme. The polarization is analyzed with a sextupole magnet and its overall value is 0.70 for an intensity of 1×10¹⁴ atms s⁻¹. By reversing the sense of circular polarization of the pumping light the atomic beam polarization is easily reversed in direction.     

Efficient and high-power intracavity frequency doubled diode-side-pumped Nd:YAG/KTP continuous wave (CW) green laser

Highly efficient continuous wave (CW) green beam generation by intracavity frequency doubling of a diode side-pumped Nd:YAG laser using a single pump head based on a copper-coated flow tube in a V-shaped cavity geometry has been demonstrated. A maximum 30.5 W of CW green power was obtained at a total diode pumping power of 260 W corresponding to 11.7% conversion efficiency of diode pump power to CW green power and 4.7% conversion efficiency of electrical power to CW green power. The performance of the laser by considering the pump power induced thermal lensing effect and the M²-parameter at the fundamental wavelength has been analyzed.