GaInAsSb/AlGaAsSb lasers in the wavelength range between 2.73 μm and 2.93 μm

Compressively strained multiple quantum well lasers in the GaInAsSb/AlGaAsSb material system are reported. Indium concentrations between 40% and 47.5% were chosen for the GaInAsSb quantum wells. Compressive strains varied between 1.16% and 1.43%. The lasers worked continuous wave at room temperature up to a wavelength of 2.81 μm. For a laser with 2.93 μm wavelength continuous wave operation was found up to a temperature of −23°C. This laser worked in pulsed operation at 15°C.     

A compact autocorrelator for the wavelength range between 4 and 10 μm

A compact autocorrelator suitable for the measurement of the optical pulse length of the infrared free electron laser (IR-FEL) at the S-DALINAC is described. It allows to investigate the energy transfer process from the electrons into the laser light within the undulator of the FEL. The autocorrelator utilizes the second harmonic generation (SHG) and it provides the possibility of a background-free measurement at wavelengths between 4 and 10 μm. Simulations for three different crystals used for SHG show that the largest efficiency for SHG and the best temporal resolution is achieved with a ZnGeP₂ crystal at a length of 2 mm. A test experiment at the free electron laser for infrared experiments confirmed the expected high efficiency of about 7.5% of SHG for the ZnGeP₂ crystal as well as the easy handling and fast adjustment of the system.     

Multi-order diffractive optical elements for achromatic interconnections at 1.30 μm and 1.55 μm

We propose a class of diffractive components allowing free-space optical systems to operate at the two telecommunication wavelengths simultaneously. These are fifth order diffractive components working at the sixth order at 1.30 μm and at the fifth order at 1.55 μm. Simulation results showing the link efficiency between two single-mode fibres as a function of the wavelength are presented. The width of the two transmission windows depends on the architecture of the whole system, which must be designed in accordance with technological realizability.     

Common black coatings – reflectance and ageing characteristics in the 0.32–14.3 μm wavelength range

The diffuse and regular reflectances of five optically absorbing coatings frequently used in optical systems, were measured over the 0.32–14.3 μm wavelength range, before and after exposure to heat and intense optical radiation. The measured coatings included Nextel Velvet Black, an anodised coating and NPL Super Black. The anodised coating exhibited substantial variations in its diffuse and regular reflectance values after thermal and simulated solar ageing. Solar and thermal ageing of the Nextel Velvet Black resulted in increases of its reflectance. However, thermal ageing tended to decrease the reflectance of the other paint samples examined. Thermal and solar ageing of the NPL Super Black resulted in only minor changes in its reflectance characteristics. All measurements are traceable to the UK National Standards.     

Design and fabrication of ultra broadband infrared antireflection hard coatings on ZnSe in the range from 2 to 16 μm

In conventional infrared multilayer antireflection coatings (MLAR) materials of fluoride and chalcogenide types are used, which are disadvantaged due to their low mechanical strength and poor stability against humidity and environmental impacts. In this paper, we show that high performance ultra broadband and hard infrared multilayer antireflection coatings on ZnSe substrates in the wavelength range from 2 to 16 μm can be designed and fabricated. Diamond-like carbon (DLC) hard coating as a mechanical and environmental protection layer was proposed and deposited onto MLAR surfaces (MLAR + DLC) using a pulsed vacuum arc ion deposition technique. The thickness of the high optical quality DLC can be optimized in the design simulation to achieve a practically best antireflection and surface protection performance. We show that a germanium thin film (15 nm) between the MLAR and DLC surfaces can be used as a transition layer for optical and material match. The average transmission of the fabricated MLAR+DLC surfaces was 93.1% in the wavelength range between 2 and 16 μm. The peak transmission was about 97.6%, close to the simulated values. The durability and stability against mechanical impacts and environmental tests was improved significantly compared with the conventional infrared windows.     

Megawatt peak power 8–13 μm CdSe optical parametric generator pumped at 2.8 μm

Infrared pulses, continuously tunable in the 8–13 μm range, and with up to 1 MW peak power, have been achieved using single-stage frequency conversion in a CdSe travelling-wave optical parametric generator, pumped by 100 ps pulses from an actively mode-locked, Q-switched and cavity dumped 2.8 μm Cr,Er:YSGG laser. The external quantum conversion efficiency reached 10%.     

Room temperature 2 μm Tm,Ho : YLF laser

We present the results obtained with a Tm,Ho : YLF crystal, grown in the new crystals growth facility realized in the Dipartimento di Fisica of the Università di Pisa. The 2 μm laser performance has been studied for three different pump sources, a Ti : Sapphire, a diode—tuned at 792.7 nm—and a Co : MgF₂ laser, tuned at 1.682 μm.     

Pulsed first-overtone CO laser: effective source of IR radiation in spectral range of 2.5–4.0 μm

Spectral properties of radiation of a pulsed electron-beam controlled discharge laser operating on the first-overtone transitions (Δv=2) of CO molecules have been studied both experimentally and theoretically. Various sets of dielectric mirrors with high reflectivity in the wide range of overtone spectrum have been used for the laser resonator. Multiwavelength lasing has been obtained in the wide spectral range of 2.5–4.0 μm. Efficiency of the laser operating on few vibrational transitions within a relatively narrow spectral range comes up to 5% at entirely suppressed fundamental band (Δv=1) lasing. Spectral characteristics of the overtone laser operating on a selected set of vibrational transitions have been analyzed theoretically. A comparison of the experimental and theoretical data has been made.     

Performance of CW NYAB laser at 1.06 μm end-pumped by a high-power diode-laser-array

A CW NYAB laser at 1.06 μm end-pumped by a high-power diode-laser-array has been demonstrated. At the incident pump power of 11 W, a maximum output power of 3.2 W was achieved, resulting in an optical conversion efficiency of 29.1%, and average slope efficiency of 37.5%. The output beam quality factor was measured to be M²=1.9. The internal losses caused by the NYAB crystal were measured to be 0.035 cm⁻¹. The NYAB crystal was also found to exhibit very strong thermal lensing under high-power end-pumped conditions.     

Silicon as a standard material for infrared reflectance and transmittance from 2 to 5 μm

We have investigated the specular reflectance and transmittance of polished, high-resistivity single-crystal Si in the spectral range from 2 to 5 μm. Measurements were performed with a nearly collimated (≈0.7° divergence) beam at angles of incidence from 12° to 80°, and a spectral resolution of 16 cm⁻¹. The measured values agree with the expected values obtained from the published index of refraction of Si to within 0.002. This represents a substantial reduction in experimental uncertainty compared to previous results and demonstrates the usefulness of Si as a standard material for infrared reflectance and transmittance.     

On the growth conditions of 3–5 μm well-doped AlGaAs/AlAs/GaAs infrared detectors and its relation to the photovoltaic effect studied by transmission electron microscopy

In this work, we investigate the influence of the molecular beam epitaxy (MBE) growth conditions (substrate temperature and arsenic flux) on the photovoltaic (PV) behavior and asymmetric characteristics of nominally identical well-doped AlGaAs/AlAs/GaAs double-barrier quantum well infrared photodetectors. This PV effect, already studied and reported in the literature, has been attributed to unintentional asymmetries of the potential profile introduced during the MBE growth process; in particular, due to an inequivalence of the AlAs layer properties or, more plausibly, to local space-charge regions originating from silicon segregation. The different “unintended” asymmetries for the samples considered in this work, validated by both dark-current and responsivity measurements, point at first glance to the existence of structural dissimilarities affecting the PV response. Hence, in order to clarify the influence of the suggested AlAs barriers inequivalence or interface roughness and quality in the origin of the PV signal we have performed a direct layer structural characterization by cross-section high resolution transmission electron microscopy. The analysis yields that regardless of the different growth conditions, the layers properties are similar, suggesting they play a minor role in the origin of the PV effect. Also this characterization tool may provide a further evidence of Si segregation being the main responsible. Concerning its growth conditions dependence, it seems that the As flux, and not only the substrate temperature, may affect Si segregation and hence the PV response.     

Anomalous polarization dependence of the photon drag and optical rectification fields inn-type gallium phosphide

The photon drag and optical rectification response fromn-type gallium phosphide containing 2.4×10¹⁶ electrons cm^–3 has been studied using laser sources at 10.61 and 2.83m. By using different contact configurations, the existence of an additional electric field term in the propagation direction has been deduced. This field is shown to arise from the spatial derivatives of the photon drag and optical rectification field components caused by absorption of the radiation. The importance of this effect in detector design is considered.     

IR-Emissionsspektrum eines Argon-Plasmastrahls zwischen 4 und 25 μm

The infrared emission spectrum of an argon plasmajet was investigated in the wavelength range from 4 to 25 microns by means of a Fourier-transform spectrometer. Besides numerous sharp emission lines of argon (FWHH = 1 cm^?1) several broad intensity maxima are observed at 4.636 μm, 7.435 μm and 12.346 μm with a FWHH of 7; 20 and 39 cm^?1.     

The Hot Bands of Methane between 5 and 10 μm

Experimental line intensities of 1727 transitions arising from nine hot bands in the pentad–dyad system of methane are fitted to first and second order using the effective dipole moment expansion in the polyad scheme. The observed bands are ν₃− ν₂, ν₃− ν₄, ν₁− ν₂, ν₁− ν₄, 2ν₄− ν₄, ν₂+ ν₄− ν₂, ν₂+ ν₄− ν₄, 2ν₂− ν₂, and 2ν₂− ν₄, and the intensities are obtained from long-path spectra recorded with the Fourier transform spectrometer located at Kitt Peak National Observatory. For the second order model, some of the 27 intensity parameters are not linearly independent, and so two methods (extrapolation and effective parameters) are proposed to model the intensities of the hot bands. In order to obtain stable values for three of these parameters, 1206 dyad (ν₄, ν₂) intensities are refitted simultaneously with the hot band lines. The simultaneous fits to first and second order lead to rms values respectively of 21.5% and 5.0% for the 1727 hot band lines and 6.5% and 3.0% for the 1206 dyad lines. The band intensities of all 10 pentad–dyad hot bands are predicted in units of cm⁻²atm⁻¹at 296 K to range from 0.931 (for 2ν₄− ν₄) to 7.67 × 10⁻⁵(for 2ν₄− ν₂). The total intensities are also estimated to first order for two other hot band systems (octad–pentad and tetradecad–octad) that give rise to weak transitions between 5 and 10 μm.     

Laser magnetic resonance of the O2 molecule at 699 μm

A new highly sensitive far infrared optically pumped laser magnetic resonance (LMR) spectrometer has facilitated the observation of 21 transitions in O₂ at 699 μm (428.6285 GHz). All of these transitions involve N = 3 ← 1 of the oxygen molecule in its electronic ground state, X³Σ_g⁻. Of these 21 lines, 10 are due to the ¹⁶O₂, v = 0; 5 are due to the ¹⁶O₂, v = 1; 5 are due to the ¹⁶O¹⁸O, v = 0; and 1 set of 6 hyperfine components is due to the ¹⁶O¹⁷O, v = 0. From the intensity of the observed lines the sensitivity limit of this LMR spectrometer is found to be about 10⁻⁹ cm⁻¹ at this frequency with a 1-sec time constant.     

High temperature (T>300 K) light emitting diodes for 8–12 μm spectral range

Contrary to conventional light emitting diodes for visible and very near infrared utilizing interband (ω>E_g) luminescence, the longer infrared emitting diodes (LIREDs) we describe here utilize intraband (ω<E_g) electron transitions and emit beyond the fundamental absorption range of the material used. Made of indirect band gap semiconductors (like Ge, Si) and, therefore, free from the Auger recombination impact, LIREDs efficiently operate at higher temperatures (T>300 K) in the longer wavelength atmospheric window (8–12 μm). Electrically modulated power emitted is comparable to that for black body sources whereas shorter rise–fall times are due to recombination processes (200 μs) and not dependent on pixel thermal mass and thermal conduction. LIREDs can be made of different semiconductor structures provided the controllable modulation of free carrier concentration in the device base is achieved. The main parameters of Ge based LIREDs under injection mode are reported.     

Investigation of 1.3 μm emission in Nd-doped bismuth-based oxide glasses

Nd₂O₃-doped 43Bi₂O₃–xB₂O₃–(57−x)SiO₂–1.0Nd₂O₃ (x=57, 47, 39, 28.5, 19.5, 10, 0 mol%) bismuth glasses were prepared by the conventional melt-quenching method, and the Nd³⁺: ⁴F_3/2→⁴I_13/2 fluorescence properties had been studied in an oxide system Bi₂O₃–B₂O₃–SiO₂. The Judd–Ofelt analysis for Nd³⁺ ions in bismuth boron silicate glasses was also performed on the basis of absorption spectrum, and the transition probabilities, excited-state lifetimes, the fluorescence branching ratios, quantum efficiency and the stimulated emission cross-sections of ⁴F_3/2→⁴I_13/2 transition were calculated and discussed. The stimulated emission cross-sections of 1.3 μm were quite large due to a large refractive index of the host. Although the effective bandwidths decreased with increasing SiO₂ content, quantum efficiencies and stimulated emission cross-sections enhanced largely with increasing SiO₂ content.     

External cavity quantum dot tunable laser through 1.55 μm

The optical performance of InAs/InGaAsP quantum dot (QD) lasers grown on (1 0 0) InP was studied for three different material structures. The most efficient QD laser structure, having a threshold current of 107 mA and an external differential quantum efficiency of 9.4% at room temperature, was used to form the active region of a grating-coupled external cavity tunable laser. A tuning range of 110 nm was demonstrated, which was mainly limited by the mirror and internal losses of the uncoated laser diode. Rapid state-filling of the QDs was also demonstrated by observing the evolution of the spectra with increasing injected current.     

Infrared absorption by acetylene in the 12–14 μm region at low temperatures

Spectral transmittance measurements have been performed on N₂-broadened lines of ¹²C₂H₂ and ¹²C¹³CH₂ in the 13.7 μm region at 153,200, and 296 K. From line-by-line comparison of observed and computed spectral transmittance, line strengths, half-widths, and their dependence on temperature have been deduced for conditions relevant to the atmospheres of Jupiter, Saturn, Titan, and Earth.