1.24-μm cascaded Raman laser for 1.31-μm Raman fiber amplifiers

Received: 10 November 1997     

Waveform of the amplitude modulated laser light by means of a mechanical chopper

The model which reproduces accurately and conveniently the waveform of the amplitude modulated cw laser light in the TEM₀₀ mode by a mechanical chopper is developed. It is found that its predictions are in good agreement with the strict, completely accurate but rather lengthy and inconvenient treatment and with the experiment. The criterion for the efficient amplitude modulation of the laser light by a mechanical chopper is formulated.     

Achievement of laser fusion of biological cells using UV pulsed dye laser beams

This paper reports a successful achievement of laser-induced biological cell fusion using an excimer laser excited dye laser. To our knowledge, we examined for the first time the dependence of fusion rate on laser pulse energy, number of laser pulses, and laser wavelength. Maximum fusion rate of approximately 50% was obtained by this laser fusion technology.     

Influence of end reflectivity on gain saturation in a planar distributed feedback laser

An approximate method for the analysis of planar-waveguide distributed-feedback lasers is extended to include a nonvanishing reflectivity at the ends of the structure. An index grating structure with parasitic losses is investigated. An expression for the small-signal gain coefficient ^0MN as a function of the output power P ^MNout normalized to the saturation power P ^s , coupling coefficient K, complex reflectivity R of end reflectors, and waveguide parameters is presented.     

A simple laser linac

When a laser is focused by a lens or mirror array the field acquires a longitudinal component. Under certain conditions this longitudinal laser field could be used to accelerate an injected particle to high energies.     

Conditions for the harmonic-like and efficient amplitude modulation of the cw gaussian laser beam by means of a mechanical chopper

The values of the chopping disc slot and mark space widths relative to the radius of the Gaussian beam are found, which achieve optimum harmonic-like and efficient amplitude modulation of the cw laser beam. The simple approximation for the waveform of the modulated laser power valid for these optimum or near optimum values of the chopping disc parameters is presented.     

Amplitude modulation of the cw laser light in the TEM mn mode by means of a mechanical chopper

Amplitude modulation of the laser beam in a TEM _mn mode by means of a mechanical chopper is investigated on the basis of the chopping model represented by a moving system of infinitely long, parallel slots and mark spaces. The cases of rectangular and axial symmetry of the laser beam are both treated. The explicit expressions for the waveform of the modulated normalized transmitted laser power are deduced and their consequences investigated. It is found that in the case of rectangular symmetry, unlike the case of axial symmetry, the TEM _mn modes give, for a constant value of the mode numbern and for any value ofm, the same time dependence of the amplitude modulated laser power. The notion of the equivalent modulation widths is introduced and conditions for the efficient amplitude modulation are found.     

Optical bistability polarization dependences with an interference modulator

Polarization-dependent hysteresis of a bistable device on the base of an electrooptical modulator at oblique incidence of light is observed. The device switching is performed by variation of the incident light polarization. The multistable character of the transmitted light polarization is discussed.     

Full-automatic broad-band wavelength control of a pulsed dye laser

A full-automatic wavelength controled pulsed dye laser has been developed. With the control system, dye laser oscillations of nanosecond pulses are tuned to any wavelength in the visible or scanned in any sweep mode keeping the nearly transform-limited bandwidth of 0.45 GHz. A mechanical tuning of the wavelength is employed, such that the motion of three wavelength selectors is synchronized to give a smooth and precise wavelength control. The basic principle underlying the tuning scheme, various requirements to be met in system construction, and the practical performance of automatic wavelength control are described in this paper.     

A laser optical method for the determination of tropospheric OH concentrations

A long-path absorption procedure for the determination of tropospheric OH concentrations is described in detail. Initial measurements using this method were carried out in Frankfurt a. M. By including in the evaluation the visible radiation of a frequencydoubled dye laser used in the measurements, it was possible to mathematically reduce the signal fluctuations caused by the scattering and density fluctuations of tropospheric air. The resulting detection limit was 3×10⁶ OH per cm³. SO₂ concentrations which had to be simultaneously determined in order to eliminate an interference effect, could be detected in the range of 1–40 ppb on the absorption path.     

A model for the optimization of double-clad fiber laser operation

Received: 27 October 1997/Revised version: 12 January 1998     

Ultrafast ytterbium-doped bulk lasers and laser amplifiers

We review recent achievements with ultrafast bulk lasers and amplifiers based on Yb:YAG and Yb:glass. Special attention is paid to those aspects of the quasi-three-level nature of these gain media that are important for short-pulse generation. The potential of Yb-doped media for efficient short-pulse generation and amplification is compared to their Nd-doped counterparts. Received: 4 January 1999 / Revised version: 15 March 1999 / Published online: 26 May 1999     

Schlieren diagnostics of the plasma focus using a mode-locked dye laser

By means of schlieren techniques the discharge characteristics of a 1 kJ plasma focus device were investigated. Different inner electrodes were used with diameters ranging from 4 mm to 10 mm and the working gases were hydrogen and neon. A spatial resolution in the m region and a temporal resolution in the ps region could be achieved using a mode-locked dye laser as schlieren light source. During the run-down and collapse phase of the discharge the spatially and temporally resolved electron density was determined from the schlieren pictures by means of numerical simultations of the beam deflection by the plasma. During the focus phase the temporal development of the plasma could be observed.     

Optimum gain length for pulsed dye laser amplifiers

It is shown analytically that for a pulsed dye laser amplifier, transversely pumped by a short duration pulsed laser, there exists an optimum gain length of the amplifier at dye laser wavelengths at which ground state absorption does not vanish. Thus, if the available pump power is distributed over this gain length, the extraction efficiency and the saturated gain of the amplifier reaches a maximum. The dependence of the extraction efficiency and gain on the amplifier length is strongly affected by the nonlinear absorption of the dye laser arising from excited state absorption, subsequent to ground state absorption.     

Experimental results on the photophoretic motion and radiometric trapping of particles by irradiation with laser light

An experimental observation of the photophoretic motion of micro-sized particles suspended in air has been performed using the radiometric force from a continuous laser beam. The irradiation was used to trap the particles in a confined optical field and to levitate them. Complex photophoretic motion of the particles was observed in the focus of the beam.     

3D Modeling of amplification processes in CPA laser amplifiers

We present here chirped pulse amplification simulations allowing for the extension of the generally used 1D model. The importance of the beam spatial profiles, diffraction and thermal effects in simulations is clearly shown in order to describe with accuracy the gain saturation. Experimental measurements performed on a 100 TW laser validate this calculation. The effects of dispersion and self-focusing are also studied.This revised version was published online in August 2005 with a corrected cover date.     

Controlled dumping of pulses of laser radiation ranging from MIR to the MM by means of optical semiconductor switching

A simple method to produce sub-ns pulses of laser radiation with wavelength ranging from middle infrared (MIR) to millimeter (MM) is experimentally demonstrated. The system operates with a single OSS (optical semiconductor switching) driven by a ns Nd laser. Pulse control is produced by varying the distance of a mirror from an OSS used as a cavity dumping. The effectiveness of this sub-ns MM pulse generation is larger than the one observed in other schemes. Pulses with 500-ps FWHM and 15-W power were produced at 2.65 mm with a time compression compared to the 2-ns FWHM of the 1.06-μm driving laser. Received: 30 October 2000 / Revised version: 26 January 2001 / Published online: 9 May 2001     

The conditions for total reflection of low-energy atoms from crystal surfaces

A single-mode dye laser is described in which a “double Michelson” mode selector is used instead of intracavity Fabry-Perot systems. This simple device gives a lower threshold, a high single-mode power (≳250 mW), and a good geometrical quality of the laser beam. Synchronous pressure scanning of the cavity and the mode selector frequencies makes it possible to continuously sweep the optical frequency over 40 GHz without any difficulty. Another version, in which one mirror of the “double Michelson” has been replaced by a retroreflecting optical grating, is also reported. In this case, no selective element (Lyot filter, wedge, ...) has to be inserted in the laser cavity.     

Development of an optical time scale

A time standard based on the use of an optical oscillation period of a frequencystable He–Ne laser as a time scale is first described. We obtained highly frequency-stable oscillations in the SHF range that were locked to the oscillations of a He–Ne laser stabilized to an absorption resonance in methane at 3.39 m. A direct comparison of frequency stabilities of a rubidium standard and He–Ne/CH₄ laser has been made. The absolute measurement of the frequency of the He–Ne/CH₄ laser we performed gave a new value of frequency.This work was reported at the 3rd Frequency Standards and Metrology Symposium     

Nonlinearities in semiconductor laser amplifiers

This review discusses the physical mechanisms of absorptive and dispersive nonlinearity in amplifiers resulting from interband and intraband electron transitions, with an assessment of the relative strengths and response times of these nonlinearities. Where appropriate, the potential applications of these nonlinearities in optical networks are also indicated.