Internal conical refraction of Bessel light beams

The internal conical refraction of a Bessel beam of arbitrary order is studied theoretically. It is shown that a beam of the order m of arbitrary polarization in the general case is partially converted to Bessel beams of the order m ± 1 with orthogonal circular polarizations. Conditions for complete conversion of a beam of the order m to a Bessel beam of the order m?1 or m+1 are determined.     

Efficient conical emission of stimulated Raman Stokes light generated by a Bessel pump beam

Stimulated Raman scattering in H(2) gas was studied with a Bessel pump beam, which was generated with a binary phase grating. The first Stokes light was emitted along the surface of a cone, the angle of which was equal to the cone angle of the Bessel pump beam multiplied by the ratio of the wavelengths of the Stokes and pump beams. High conversion efficiency into the first Stokes light of as much as 60% was achieved, indicating that the complete Bessel J(0) mode of the pump beam is involved in the stimulated scattering process.     

A controlled conical lens for the formation of Bessel light beams

The possibility of the formation of zero-order Bessel light beams using a uniaxial crystal with cylindrical electrodes is investigated. It is shown that, if a given polarization distribution is provided in the incident beam, a Bessel light beam with the cone angle controlled by an external electric field is formed. It is proposed to use this result for the matching of the axicon parameters and creation of conical lenses with an adjustable cone angle.     

圆锥气泡声致发光光脉冲和光谱

对一种U形管圆锥气泡发光装置进行了改进，使其发光效果更好，利用光电倍增管和光谱仪 得到了水中空气圆锥气泡的发光脉冲和发光光谱图. 得到的发光脉冲在几百个ps和几个ns之 间不等；在近红外波长范围内观测到了水分子振动能级的特征谱，其连续谱发光强度随着波 长的增加而升高. 另外还得到了在水中加入NaCl溶液的气泡发光光谱图. 关键词： 声致发光 圆锥气泡 光脉冲 光谱     

Femtosecond Bessel light pulse formation by a multi-circular diaphragm

The dynamics of the envelope of a new type of light field, a femtosecond Bessel light pulse (FBLP) formed from a Gaussian pulsed beam by means of a multi-circular diaphragm, has been investigated theoretically. It is shown that the FBLP possesses a steady structure that features a narrow central maximum and significantly suppressed subordinate maxima.     

Negative feedback using a nonlinear mirror for the generation of a long train of short light pulses

A nonlinear mirror is used to provide a passive negative feedback in an actively mode-locked pulsed Nd:YAG laser. Trains of 250 ps pulses with a total length of up to 50 microseconds were generated. The train duration is limited only by the flashlamp pump pulse length.On leave from Department of Physics, University of Sofia, BG-1126 Sofia, Bulgaria     

Study of reflection of light by a moving mirror

The law of reflection of light by a moving mirror in the case of special Lorentz transformation is well known. We have derived the law of reflection of light by a moving mirror in the case of the most general Lorentz transformation. It has been observed that in the case of special Lorentz transformation, the law of reflection of light by a moving mirror is very simple but in the case of the most general Lorentz transformation, the law of reflection of light by a moving mirror is very complex.      

Colored conical emission by means of second-harmonic generation

We predict that the combination of space and time modulational instabilities that occur by means of parametric wave mixing in quadratic media leads to colored conical emission. This phenomenon should be observed under conditions usually employed in second-harmonic experiments.     

Generation of nondiffracting Bessel beams by use of a spatial light modulator

A laser beam with phase singularities is an interesting object to study in optics and may have important applications in guiding atoms and molecules. We explore the characteristics of a singularity in a nondiffracting Bessel beam experimentally by use of a programmable spatial light modulator with 64-level phase holograms. The diffraction efficiency with 64-level phase holograms is greatly improved in comparison with that obtained with a binary grating. The experiments show that the size and deflection angle of the beam can be controlled in real time. The observations are in agreement with scalar diffraction theory.     

Pedestal suppression of ultrashort pulses by using a birefringent nonlinear polarization rotation mirror

A new scheme for a birefringent nonlinear polarization rotation mirror is proposed for pedestal suppression of ultrashort pulses. Environmentally stable and precisely controllable operation is demonstrated. The main pulse and pedestal components are separated and picked out from the different ports. By use of the soliton effect and nonlinear polarization rotation, almost transform-limited pedestal-free 318 and 143 fs ultrashort pulses with peak powers of 0.9 and 1.7 kW are successfully generated. The maximum pedestal-suppression ratio is 24 dB, and the pick-out efficiency is up to 46% including coupling loss. The characteristics are analyzed both experimentally and numerically.     

Efficient generation of Bessel beam arrays by means of an SLM

We use a Spatial Light Modulator (SLM) to produce arrays of Bessel beams by using multiple axicon phase-masks on the SLM. This approach utilises the whole of the SLM, rather than just a thin annular region (which is the case if the SLM is in the far-field of the generated Bessel beams). Using the whole SLM rather than just an annular region means that the required intensity on the SLM is an order of magnitude lower for a given power in the Bessel beams. Spreading the power over the whole SLM is important for high-power applications such as laser micromachining. We allow the axicons to overlap and interfere in the hologram, so the axial length of the Bessel beam core is maintained as we add more beams to the array.     

Probing of ultrasonic pulses by multidirectional light

An acousto-optical reconstruction method for acoustic signals using multidirectional light diffraction by finite amplitude ultrasonic pulses is presented. When crossing the ultrasonic field, the far field diffracted laser light intensity of an incident convergent lightbeam becomes modulated in time. It is found that for special conditions, concerning direction of observation, ultrasonic frequency, power level and interaction length, the modulated light intensity is almost an exact copy of the diffracting acoustic pulse. Reconstruction can be completed by applying a fast Fourier transform (FFT) routine. Examples are provided and applications of this optical probing technique are suggested.     

Colored conical emission in BBO crystal induced by intense femtosecond pulses

We present the experimental and theoretical study of colored conical emission (CCE) during intense femtosecond pulses propagating in a β-barium borate (BBO) crystal. CCE revealed special nonlinear dynamics of the strong coupling between the fundamental and second harmonic pulses due to the spatiotemporal modulation instability (MI). The underlying physics of CCE involve three three-photon processes, according to which the beam angular spectra was calculated on the phase-matching conditions and accords with the experimental observation.     

Adaptive shaping of two-cycle visible pulses using a flexible mirror

We present a double-pass non-collinear optical parametric amplifier (NOPA) that delivers 4-fs visible–near-infrared pulses. The paper discusses geometrical and temporal properties of the NOPA configuration, which allow us to broaden the gain band of simultaneous parametric amplification in excess of 250 THz. The key elements of the bandwidth enhancement include (i) the use of a broadband second-harmonic pump, (ii) optimization of the incidence angle of all monochromatic spectral components of the pump in order to produce a favorable offset of the corresponding phase-matching curves, and (iii) selection of the chirp rate and time delay between the stretched pump and seed pulses. We next devise a two-stage compressor that incorporates a flexible mirror for adaptive pulse shaping and develop a simple and trustworthy feedback loop based on a one-dimensional spectral measurement. Our rapid numerical algorithm for adaptive control of the flexible membrane is found superior to more complex search routines that are less resistant to the fluctuations of the laser intensity. The automated optimization procedure results in the generation of two-cycle pulses with a carrier wavelength at ∼600 nm. The absence of deep modulation on the parametrically amplified spectrum in combination with the adaptive phase correction lead to a high quality of the temporal profile and allow concentrating 90% of the pulse energy within only a 7.5-fs time window. Received: 8 April 2002 / Revised version: 26 June 2002 / Published online: 25 September 2002 RID="*" ID="*"Present address: Institut für Photonik, Technische Universit?t Wien, Gusshausstrasse 27, 1040 Vienna, Austria RID="**" ID="**"Corresponding author. Fax: +81-3/5841-4165, E-mail: kobayashi@phys.s.u-tokyo.ac.jp     

Colored conical emission by means of second harmonic generation in a quadratically nonlinear medium

Colored conical emission was observed experimentally in a thick beta-barium borate crystal as a result of spatiotemporal modulational instability. In the presence of both dispersion and diffraction, colored conical emission showed specific features that were characteristic of the nonlinear dynamics of the strongly coupled fundamental and harmonic fields. Experimental observation directly demonstrated that beam angular spectra were substantially modified as a result of exponential growth of perturbations by means of parametric wave mixing. Seeded amplification of colored conical emission was demonstrated to support ultrabroadband up-conversion.     

Formation of x-ray images by means of thermal action of a light beam on the surface of a diffracting crystal

The results of experimental investigations of the formation of the spatial structure of x-ray diffraction beams (x-ray images) from the KDP crystal surface under its illumination by a light beam spatially modulated in intensity are presented. A simulation of the x-ray image, depending on the parameters of the diffraction peak of a crystal and on the conditions of the creation of a temperature deformation field at its surface, has been carried out.     

Lidar dynamic range compression by using a membrane mirror light shutter

A lidar system employing a membrane mirror light shutter, MMLS, for dynamic range compression is demonstrated in this paper. The use of the MMLS allows the dynamic range of the lidar to be compressed by more than 2 orders of magnitude and, at the same time, the strong near-field optical return is avoided. Important parameters for an MMLS used in lidar are described and their measurements in a lidar configuration are presented. The decompression in the lidar data retrieval caused by using the MMLS is discussed.     

Generation of a directed nanolocalized photoelectron beam by means of femtosecond laser pulses

A directed photoelectron beam is obtained when photoelectrons from a sharp metal tip irradiated by femtosecond laser pulses are passed through a quartz nanocapillary. Such a nanolocalized photoelectron train makes it possible to conduct experiments with simultaneous femtosecond time and nanometer spatial resolutions.