Studies of interfacial regions by sum-frequency generation with a free-electron laser

The use of a Free-Electron Laser (FEL) allows the study of (non)linear optical properties of materials over unsurpassed large spectral intervals. As an example, we report on the use of a FEL as the infrared source in spectroscopic infrared-visible Sum-Frequency Generation (SFG). Employing the extremely wide tunability of the Free-Electron Laser for Infrared eXperiments (FELIX) at Rijnhuizen, we have studied the frequency dependence of the nonlinear susceptibility for sumfrequency generation in gallium phosphide between 20 and 32 m in great detail. We have developed a shortpulse visible laser system that is highly synchronous with FELIX thereby creating a two-color setup that can be broadly applied. Resonantly enhanced SFG in alphaquartz has been used to study the relative timing stability of FELIX and the synchronized picosecond-laser system.Paper presented at the 129th WE-Hearaeus-Seminar on Surface studies by Nonlinear Laser Spectroscopies, Kassel, Germany, May 30 to June 1, 1994     

An 8.1 W diode pumped solid-state quasi-continuous-wave yellow laser at 589 nm by intracavity sum-frequency mixing generation

We report an L-shaped symmetrical co-folding-arm plane-plane diode pumped solid-state yellow laser at 589 nm by using intracavity sum-frequency mixing. By carefully designing the cavity and employing various techniques to optimize the laser’s specifications, a quasi-continuous-wave (QCW) free-oscillation yellow laser source, which has an average output power of 8.1 W, a beam quality factor of M² = 2.3, and a repetition rate of 1.1 kHz, is developed. The generation of yellow laser at 589 nm is achieved by intracavity sum-frequency mixing between the laser lines at 1319 nm and 1064 nm of an Nd:YAG laser in a KTP crystal. To the best of our knowledge, the 8.1 W output at 589 nm is higher than any other diode pumped solid-state yellow laser generated by intracavity sum-frequency generation so far.     

43 W picosecond laser and second-harmonic generation experiment

Combining the advantages of diode-end-pumped Nd: YVO₄ and diode-side-pumped Nd: YAG amplifiers, a high average power and high beam quality picosecond laser is designed. The system delivers a picosecond laser with average power of 43.4 W and good beam quality of M² < 1.7. By focusing the high power picosecond laser in LBO crystal, 532 nm green laser with maximal power of 20.8 W is generated and the conversion efficiency of second-harmonic generation reaches 56.4% when 17.7 W green laser obtained from the fundamental frequency laser with power of 31.4 W and beam quality of M² < 1.25.     

Generation of powerful one-picosecond dye laser pulses at two independently tunable wavelengths

Generation of powerful 1-ps pulses at two independently and continuously tunable wavelengths with precisely controllable delays between them is obtained in a compact dye laser device using a single standard nanosecond Nd:YAG pump laser.     

Efficient generation of FIR radiation by optical pumping of D2 18O

In this paper we show that D₂ ¹⁸O vapour, optically pumped with a continuously tunable high pressure CO₂ laser, is an excellent source for far infrared radiation. Both high photon conversion coefficients and broad Raman gain regions were found for a large number of new laser transitions spread over the frequency range from 25 cm^–1 to 240 cm^–1. We demonstrate that these Raman gain regions can be used to generate far infrared laser pulses with high intensity and durations of about 100 ps.     

Seven-terawatt Ti:sapphire laser system operating at 50 Hz with high beam quality for laser Compton femtosecond X-ray generation

We present a 7-TW Ti:sapphire laser system operating at 50 Hz for laser Compton femtosecond X-ray generation. This laser system delivers 8.4 W of average output power at a repetition rate of 50 Hz with a pulse width of 24 fs. It demonstrates successful management using a dynamically stable resonator in the regenerative amplifier and compensation for thermal lensing by a convex mirror in a ring-type four-pass power amplifier. We also present the results of closed-loop corrections for distorted wavefronts of amplified and compressed laser pulses, using an adaptive optical system consisting of a Shack–Hartmann-type wavefront sensor and a deformable mirror. This closed-loop correction results in dramatic improvements, reducing wavefront distortions below 0.05 λ rms. Received: 31 October 2002 / Revised version: 3 March 2003 / Published online: 5 May 2003 RID="*" ID="*"Corresponding author. Fax: +81-298/61-3349, E-mail: ito@festa.or.jp     

Optimization of grating size in chirped-pulse-amplification. laser system

We performed calculations for a chirped-pulse-amplification laser system with a sub-100-fs pulse duration including the finite size of gratings in an aberration-free stretcher/compressor design. Both the higher-order phase dispersion and the spectral clipping, which is due to the finite size of the optics in the stretcher and the compressor, are taken into account in the calculation. We discuss the influence of both phase dispersion and spectral clipping on the important parameters of the recompressed pulse, such as pulse duration, pulse contrast, and peak intensity, employing different phase-dispersion compensation methods. The calculations show that the use of a small compressor grating reduces the higher-order phase errors and smoothes the sharp spectral cut-off caused by spectral clipping in the stretcher, which consequently improves the pulse contrast ratio of the main pulse to the pedestal. Received: 1 April 2000 / Published online: 8 November 2000     

A flashlamp-pumped 946 nm Nd:YAG laser

Generation of 946 nm radiation from a commercially available, flashlamp-pumped Nd:YAG laser was investigated. By suppression of the high-gain 1.064 m transition and with a specially designed cooling system, a stable emission at 946 nm was achieved in the temperature range 300–240 K. At a repetition rate of 10 Hz laser output powers of 100mW and 500 mW were obtained at room temperature and 240 K respectively. The temperature dependence of unsaturated gain, slope efficiency and pumping threshold were determined.S. Dimov is supported by a fellowship from the Alexander von Humboldt Foundation     

Formation of diffraction-free beams by laser generation of conical radiation in a Kerr medium

Received: 16 June 1998     

Broadly tunable femtosecond solid-state laser sources

The techniques of coupled-cavity modelocking and self-modelocking in which intensity-induced nonlinear effects are exploited have been reviewed for broad-band gain media. Particular emphases have been placed upon the archetypical colour-centre and titanium-sapphire laser configurations in which these techniques were first demonstrated and subsequent refinements are set in context. A femtosecond optical parametric oscillator pumped by a self-mode-locked titanium-sapphire laser has also been described as an exemplar of a practical means of extending the source tunability into the mid-infrared spectral region.     

Tunable picosecond infrared pulses generated by stimulated electronic Raman scattering of a mode-locked Ti:Sapphire laser in potassium vapor

A down-conversion to the mid-infrared region by using Stimulated Electronic Raman Scattering (SERS) in potassium vapor is described. The pump radiation is a frequency-doubled regeneratively amplified Ti:Sapphire laser with a pulse duration of 2 ps, pulse energy of 0.2 mJ, and repetition rate of 10 Hz. With the pumping frequency tuned around the potassium 4s-5p transition, nearly transform-limited infrared radiation tunable between 2.2 and 3.4 m has been generated with a peak infrared energy of 12 µJ, corresponding to a quantum efficiency of 17%, and with a pulse duration of 2 ps. The present tuning range could be extended by extending the tuning range of the pump laser. In comparison, intense infrared radiation of 90 µJ energy but with a very narrow tunability around 2.9 m has also been generated by SERS in barium vapor.     

A time-compensated spectral filter for transform-limited tunable picosecond pulse generation from spectro-temporal-selection dye lasers

Diffraction and transform-limited picosecond tunable pulses are generated from Spectro-temporal-Selection (STS) dye lasers by using a new extra-cavity filter. This filter is based on a grazing-incident grating and arranged in the configuration of a folded dispersive delay line. Thus, it provides both high spectral selectivity and controllable temporal compensation for elimination of pulse broadening. Direct production of diffraction- and transform-limited picosecond dye laser (10 µJ, 50 ps) pulses spectrally adjustable between 398 and 702 nm is demonstrated in a compact device, with 8 ns pump pulses from a nanosecond nitrogen laser.     

Efficient low-voltage operation of a reverse-biased autoprepulse XeCl laser

An improved version of the auto-prepulse excitation scheme for long-pulse operation of the XeCl excimer laser is reported. A pulsed reverse bias on the small peaking capacitance allows efficient (1.7%) operation at 100 mJ output level with a charge voltage limited to 5–7 kV. Analogies and differences with other long-pulse operation schemes are also discussed.     

Direct generation of sub-nanosecond pulses in a high-pressure miniature excimer laser

Direct generation of subnanosecond pulses in a 9.0 cm discharge-length high-pressure XeCl laser is reported. The shortest pulse obtained was 670 ps (FWHM) with an energy of 1.2 mJ corresponding to 1.8 MW peak power.     

Generation of high peak power excimer laser radiation by pulse shortening

Techniques for shortening the pulses of a commercial oscillator-amplifier excimer laser have been investigated. By a combination of a H₂-Raman cell and a saturable absorber dye jet the oscillator pulses are shortened from about 25 ns to typically 1.5 ns. Upon amplification pulses around 3.5 ns with peak powers of more than 100 MW for KrF (248 nm) and 25 MW for XeCl (308 nm) are obtained.     

Efficient rotational Raman conversion of XeCl laser radiation in H2

2 is investigated with a XeCl laser. It is shown that energy conversion to rotational Stokes radiation can be efficiently obtained by properly choosing the focusing geometry of pump radiation and the pressure of the Raman medium even at moderate pulse energies. Energy conversion to the first rotational Stokes at 313.8 nm with efficiencies as high as 38% is obtained with a circularly polarised XeCl pump beam of 10-mJ energy focused in 30 bar of H₂. The spectral and optical characteristics of the pump and the rotational Stokes radiation are analysed. Received: 29 May 1996/Revised version: 7 March 1997     

Measuring the temporal intensity of ultrashort laser pulses by triple correlation

Received: 13 May 1997/Revised version: 1 August 1997     

Preliminary studies of radiation coupling between remote soft X-ray laser amplifiers

Coupling of a soft X-ray laser beam with a relaying concave mirror in a sequentially pumped amplifier geometry using the Ne-like Ge system has been studied experimentally. Preliminary observations indicate an increase in the spatial coherence of the amplified relayed beam. In addition, near-field imaging of one of the amplifier plasmas shows a double-lobed intensity pattern of the emergent beam indicating refractive guiding of the amplified beam with components both normal and tangential to the target surface.     

Generation of coherent ultraviolet radiation in the 330 nm region by multiphoton excitation of sodium vapor

We report the observation of coherent uv emission at 330.2±0.5 nm when sodium vapor in a heatpipe is irradiated with a pulsed visible dye laser with output wavelength in the 570–595 nm region. It is found that intense uv emission can be produced from Na atoms as well as from Na₂ molecules. The excitation functions and their dependence on vapor density and laser power density are presented and the mechanisms for producing the emission are discussed.On leave from the Department of Physics, Fujian Normal University, Fuzhou, Fujian, People's Republic of China     

A laser system producing 5×1019 W/cm2 at 10 Hz

19 W/cm² have been achieved. Received: 10 March 1997/Revised version: 26 April 1997