Circularly polarized localized near-field radiation at the nanoscale

Diffraction-limited circularly polarized electromagnetic radiation has been widely used in the literature for various applications at both optical and microwave frequencies. With advances in nanotechnology, emerging plasmonic nano-optical applications, such as all-optical magnetic recording, require circularly polarized electromagnetic radiation beyond the diffraction limit. In this study, a plasmonic cross-dipole nano-antenna is investigated to obtain a circularly polarized near-field optical spot with a size smaller than the diffraction limit of light. A cross-dipole nano-antenna is composed of four metallic nano-rods placed at a perpendicular orientation with respect to each other. The performance of the nano-antenna is investigated through numerical simulations. In the first part of this study, the nano-antenna is illuminated with a diffraction-limited circularly polarized radiation. An optimal antenna geometry is specified to obtain an intense optical spot that satisfies two necessary conditions for circular polarization: a phase difference of 90° and a unit amplitude ratio between the electric field components in the vicinity of the antenna gap. In the second part of this study, the nano-antenna is illuminated with diffraction-limited linearly polarized radiation. It is shown that the phase difference between the electric field components can be adjusted by selecting either different antenna lengths or different gap distances in the vertical and horizontal directions. Due to the relatively short wavelength of surface plasma waves on the antenna, it is demonstrated that the phase difference can be sufficient to obtain circularly polarized light. An optimal physical configuration for the nano-antenna and the polarization angle of the incident light is identified to obtain a circularly polarized optical spot beyond the diffraction limit from diffraction-limited linearly polarized radiation.     

Waveform-controlled near-single-cycle milli-joule laser pulses generate sub-10 nm extreme ultraviolet continua

We demonstrate the generation of waveform-controlled laser pulses with 1?mJ pulse energy and a full-width-half-maximum duration of ～4 fs, therefore lasting less than two cycles of the electric field oscillating at their carrier frequency. The laser source is carrier-envelope-phase stabilized and used as the backbone of a kHz repetition rate source of high-harmonic continua with unprecedented flux at photon energies between 100 and 200?eV (corresponding to a wavelength range between 12-6?nm respectively). In combination we use these tools for the complete temporal characterization of the laser pulses via attosecond streaking spectroscopy.     

Compression of picosecond optical pulses from 1.5μm gain switched In GaAsP DFB diode laser

The experimental study of compression of picosecond optical pulses from a gainswitched InGaAsP DFB laser at 1.5μm wavelength range using a Gires-Tournois interferome-ter has been reported. Ultrashort optical pulses with pulsewidths of 6.6 ps, repetition rate of2.4GHz, and peak power in excess of 200 mW are obtained. The characteristics of a Gires-Tournois interferometer as a pulse compressor are also discussed.     

Displacement sensor based on polarization mixture of orthogonal polarized He-Ne laser at 1.15μm

Displacement sensor based on the polarization mixture and the cavity tuning of the orthogonal polarized He-Ne laser 1.15μm is presented.The power tuning curves of He-Ne laser are irregular,and it is difficult to measure the change in cavity length.The distortion of the curves is caused by the higher relative excitation compared with the He-Ne laser at 633 nm.In view of its potential for the wider displacement measuring range,a new method of displacement sensing is developed.Experiments show that displacement measuring stability based on the method of the polarization mixture is better than that of the power tuning curves. The displacement sensor achieves the measuring range of 100 mm,resolution of 144 nm,and linearity of 7×10-6 .     

Femtosecond continuum generation in bulk laser host materials with sub-μJ pump pulses

We report a comprehensive investigation of femtosecond continuum generation in single crystals of several common laser host materials. The absolute spectral energy density, pulse-to-pulse stability, pump threshold, and beam profile are studied in dependence on the focusing conditions, crystal thickness, pump pulse energy, and pump wavelength (775–1600 nm). Continuum generation is shown at repetition rates of up to 80 MHz and for pump pulse durations of up to 350 fs. In yttrium aluminum garnet (YAG), yttrium vanadate (YVO₄), gadolinium vanadate (GdVO₄), and potassium-gadolinium tungstate (KGW) thresholds below 50 nJ, plateau-like visible and infrared spectra, and higher infrared photon flux as compared to conventional materials like sapphire are found. We discuss the particular advantages of these materials for application in parametric amplification, femtosecond spectroscopy, and carrier-envelope phase stabilization.     

Self-compression of 1.8-μm pulses in gas-filled hollow-core fibers

We numerically study the self-compression of the optical pulses centered at 1.8-μm in a hollow-core fiber(HCF) filled with argon. It is found that the pulse can be self-compressed to 2 optical cycles when the input pulse energy is 0.2-m J and the gas pressure is 500-mbar(1 bar = 10~5 Pa). Inducing a proper positive chirp into the input pulse can lead to a shorter temporal duration after self-compression. These results will benefit the generation of energetic few-cycle mid-infrared pulses.     

Bulk Nd3+-doped tellurite glass laser at 1.37 μm

We have demonstrated, for the first time to our knowledge, lasing at 1.37 μm in a tellurite-based glass host doped with 0.5 mol.% neodymium: Nd³⁺:(0.8)TeO₂–(0.2)WO₃. The gain-switched laser could be operated with 59 μJ threshold pulse energy as well as 5.5% slope efficiency. As high as 6 μJ-pulses with a duration of 1.74 μs were obtained. The pulse repetition rate was 1 kHz. The emission cross section from the threshold analysis turned out to be 1.57×10^?20 cm² at 1370 nm by taking into account excited-state absorption from ⁴F_3/2 to ⁴G_7/2 energy level. Furthermore, the ratio of excited-state absorption to the emission cross section was found out to be 0.78 by using the slope efficiency value.     

Generation of 100 μJ pulses at 82.8 nm by frequency tripling of sub-picosecond KrF laser radiation

. Investigations of the efficient generation of powerful coherent radiation at 82.8 nm by frequency tripling of short-pulse KrF laser radiation are presented. Argon gas is selected as nonlinear medium due to the resonantly enhanced 3rd-order susceptibility χ⁽³⁾(-3ω,ω,ω,ω). Pulse energies of 100 μJ at 82.8 nm have been measured for a pump pulse energy of 14 mJ. An upscaling to more than 500 μJ is expected with available more powerful pump lasers. Features of this XUV source and possible applications are discussed. Received: 26 July 2002 / Published online: 15 November 2002 RID="*" ID="*"Corresponding author. Fax: +49-511/7622211, E-mail: reinhardt@iqo.uni-hannover.de     

An all-solid-state laser system for generation of 100 μJ femtosecond pulses near 625 nm at 1 kHz

Frequency doubling the output of a high-power femtosecond Cr:forsterite regenerative amplifier with >50% conversion efficiency in a temperature-tuned noncritically phase-matched LBO crystal produces femtosecond pulses of >100 μJ energy in the visible range near 625 nm at a pulse duration of about 200 fs or >65 μJ at <170 fs. Received: 29 March 1999 / Revised version: 27 April 1999 / Published online: 24 June 1999     

A trace methane gas sensor using mid-infrared quantum cascaded laser at 7.5 μm

Presented is a compact instrument developed for in situ high-stable and sensitive continuous measurement of trace gases in air, with results shown for ambient methane (CH₄) concentration. This instrument takes advantage of recent technology in thermoelectrically cooled pulsed Fabry–Perot (FP) quantum cascaded (QC) laser driving in a pulse mode operating at 7.5 μm to monitor a well-isolated spectral line near the ν4 fundamental band of CH₄. A high-quality liquid nitrogen cooled mercury cadmium telluride mid-infrared detector with time discriminating electronics is used along with a total reflection coated gold ellipsoid mirror offering 20 cm single pass optical absorption in an open-path cell to achieve stability of 5.2 × 10^?3 under experimental condition of 200 ppm measured ambient CH₄. The instrument operates continuously, and integrated software for laser control using direct absorption provides quantitative trace gas measurements without calibration. One may substitute a QC laser operating at a different wavelength to measure other gases. The instrument can be applied to field measurements of gases of environmental concern.     

A cw room-temperature Ho,Tm:YLF laser pumped at 1.682 μm

We present the results obtained with a Ho,Tm:YLF crystal grown at a new crystal growth facility in Pisa. The optical quality of the sample has been tested by studying its performance as the active medium of a laser operating at 2.06 μm. We employed three different pump laser sources: a Ti:sapphire, a diode (both tuned at 793 nm) and, for the first time, a continuous-wave Co:MgF₂ laser, tuned at 1.682 μm. At room temperature the best slope efficiency was 30 % in the case of “red” pumping, and 59 % in the case of “infrared” excitation. The typical lasing threshold is about 100 mW. Received: 14 March 2001 / Revised version: 15 June 2001 / Published online: 19 September 2001     

A 7-W diode-pumped Nd:YVO4 cw laser at 1.34 μm

A Nd:YVO₄ laser, end-pumped by a fiber-coupled diode-laser array, generates 7.3 W of output power at 1342 nm, the highest so far reported for this host crystal. The slope efficiency is 40% and the output-beam divergence is close to the diffraction limit. An important point in attaining such results is the choice of crystals with low Nd concentration. Received: 16 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +39-050/844333, E-mail: dilieto@df.unipi.it RID="**" ID="**"Permanent address: Scuola Normale Superiore, Piazza dei Cavalieri 7, Pisa, Italy     

Carrier-envelope phase stable sub-two-cycle pulses tunable around 1.8 µm at 100 kHz

We present a simple and efficient concept for the generation of ultrashort infrared pulses with passively stabilized carrier-envelope phase at 100 kHz repetition rate. The central wavelength is tunable between 1.6 and 2.0 μm with pulse durations between 8.2 and 12.8 fs, corresponding to a sub-two-cycle duration over the whole tuning range. Pulse energies of up to 145 nJ are achieved. As a first application we measure the high nonlinearity of multiphoton photoemission from a nanoscale metal tip.     

Twisted-mode single-frequency Er–Yb waveguide laser at 1.5 μm

Robust single-frequency operation of an erbium–ytterbium glass waveguide laser based on the twisted-mode technique is demonstrated. A single-mode output power of 0.7 mW with relative-intensity-noise peak value of –90 dB/Hz has been obtained.     

A 13.3-W laser-diode-array end-pumped Nd:GdVO4 continuous-wave laser at 1.34 μm

We report a high-power laser-diode-array end-pumped 0.3 at.% Nd:GdVO₄ continuous-wave laser operating at 1.34 m. The maximum output power of 13.3 W was obtained at the incident pump power of 49.2 W, giving the corresponding optical conversion efficiency of 27% and the average slope efficiency of 28.5%. The thermal focal length of the Nd:GdVO₄ crystal under the pump power from 15.3 to 50 W was measured experimentally. PACS 42.55.Xi; 42.70.Hj     

Diode-laser-array end-pumped 14.3-W CW Nd:GdVO4 solid-state laser at 1.06 μm

A diode-laser-array end-pumped efficient CW Nd:GdVO₄ laser at 1.06 μm has been developed. A low-order-mode output power of 14.3 W was obtained at the maximum available pump power of 26 W, giving an optical conversion efficiency of 55% and an average slope efficiency of 62%. The laser output beam quality factor at full pump power was determined to be M²<1.8. It is also shown that only lightly doped Nd:GdVO₄ crystals are suitable for high-power end-pumped lasers. Received: 4 May 1999 / Published online: 29 July 1999     

Gallium-nitride-based plasmonic multilayer operating at 1.55 μm

In this Letter, we have designed and fabricated a III-V semiconductor multilayer based on surface plasmon resonance (SPR) operating at the telecom wavelength. Optimization of the optogeometrical parameters and the metal/semiconductor layers required for this novel structure was conducted accurately by theoretical tools using the Maxwell equations. Technological fabrication of the device and its experimental characterizations using an evanescent coupling configuration was performed: the results have confirmed the existence of SPR associated to a sharp width response. This study could be a first step in the design of new plasmonic-semiconductor-based optical devices such as modulators and switches.     

Resistance in sub-μm size GaAs lines

The electrical resistance in GaAs submicron mesa lines have been studied as a function of the line width. Using molecular beam epitaxy two types of conducting layers were made: an n⁺-layer and a two-dimensional electron gas confined to an (AlGa)As/GaAs heterostructure. Processing of the lines was made by photolitography, electron beam litography and ion etching. Resistance data at 77 K and 300 K are discussed for line widths in the interval 0.2 to 5 μm. A size dependent conduction was found and interpreted in terms of geometry induced limitation of the effective conducting path.     

High peak power 16 μm InP-related quantum cascade laser

In this paper ～16 μm-emitting multimode InP-related quantum cascade lasers are presented with the maximum operating temperature 373 K, peak and average optical power equal to 720 mW and 4.8 mW at 303 K, respectively, and the characteristic temperature (T₀) 272 K. Two types of the lasers were fabricated and characterized: the lasers with a SiO₂ layer left untouched in the area of the metal-free window on top of the ridge, and the lasers with the SiO₂ layer removed from the metal-free window area. Dual-wavelength operation was obtained, at λ ～ 15.6 μm (641 cm^?1) and at λ ～ 16.6 μm (602 cm^?1) for lasers with SiO₂ removed, while within the emission spectrum of the lasers with SiO₂ left untouched only the former lasing peak was present. The parameters of these devices like threshold current, optical power and emission wavelength are compared. Lasers without the SiO₂ layer showed ～15% lower threshold current than these ones with the SiO₂ layer. The optical powers for lasers without SiO₂ layer were almost twice higher than for the lasers with the SiO₂ layer on the top of the ridge.