Analysis of the spectral structure of CuBr laser lines

The spectral structure of spontaneous emission of copper atom at 510.6 nm and 578.2 nm was calculated considering the hyperfine structure of energy levels and the isotope shift. The spectral structure of the 510.6 nm and 578.2 nm laser lines was measured in a sealed-off CuBr laser tube with periodic refreshment of the neon buffer gas under different work temperature and excited voltage. The spectral structure of the spontaneous emission of copper atom was found to have similar outline with its laser lines. The spectrum of the 510.6 nm laser line maintains similar outline with three peaks at various discharging parameters while the spectrum of the 578.2 nm laser line is strongly dependent on the reservoir temperature and the discharge voltage.     

Pump-dependent luminescence in the Ag nanoparticles doped by Erbium

A substantial spectral shift of the UV-laser induced luminescence in the Ag nanoparticles (NP) doped by Er³⁺ ions attached to ITO substrates was observed at T = 4.2 K. We have established high energy spectral shift of principal luminescent maxima (from wavelength equal to about 1.45 up to 1.15 μm) with increasing of the pumping nanosecond nitrogen laser power density up to 1.1 GW/cm² operating at λ = 337 nm. With increasing Erbium content with respect to Ag the spectral shift and spectral line broadening increase. It may be caused by specific features of trapping level occupation kinetics on interfaces NP/ITO substrate. The observed process is fully reversible. The luminescence is observed only during excitation by the 337 nm laser pulses and is absent for laser pulses operating at other wavelengths (like excimer laser at 218 nm and nitrogen laser at 371 nm).     

Photoabsorption cross section measurements of CO2 between 106.1 and 118.7 nm at 295 and 195 K

High-resolution vacuum ultraviolet carbon dioxide photoabsorption cross sections are required for modeling airglow emissions from the Martian and Venusian atmospheres and for photochemical models of those atmospheres. We report cross section measurements on CO₂ at 295 and 195 K between 106.1 and 118.7 nm at a spectral resolution of 0.005 nm. Significant deviations from the results of previous, lower-resolution measurements are apparent, particularly in regions of sharp spectral structure. Temperature dependence in the photoabsorption cross sections is evident throughout the region, being especially pronounced at wavelengths greater than 113 nm.     

Spectroscopic characterization of aluminum plasma using laser-induced breakdown spectroscopy

A detailed investigation of aluminum plasma induced by a 1064 nm Nd:YAG laser in air was performed. The emission of spectral lines arising from Al I transition at 396.07 nm, Al II transition at 358.46 nm, Al III transition at 360.72 nm and Al IV transition at 363.05 nm were well-resolved. The plasma parameters including electron temperature and electron density were determined through the Boltzmann plot method using the emission line intensities of the same ionized stages of aluminum atoms and the Stark-broadening profiles of Al II emission line, respectively. The temporal evolutions of the spectral lines belonging to atomic and ionic aluminum elements and the plasma parameters were investigated at three different laser pulse energies. Moreover, the validity of local thermodynamic equilibrium was elucidated in our experimental condition.     

Cross-relaxation and spectral broadening of gain for Nd/Cr:YAG ceramic lasers with white-light pump source under high-temperature operation

Spectral broadening of the fluorescence of a Nd/Cr:YAG ceramic at the 1064 nm lasing wavelength was observed, and the amplification properties at a high temperature were investigated by considering cross-relaxation. These ceramics are promising for use as a solid-laser material pumped with solar or lamp light. It has been found that whenever the temperature of a laser medium is high and a spectral shift occurs, a high small-signal gain remains owing to the broad spectral band and the cross-relaxation. This optical property is remarkably different from that of a Nd:YAG laser. For a conventional Nd:YAG laser, the bandwidth at 1064 nm is 0.45 nm, and a reduction in small-signal gain occurs at a temperature of 373 K because the spectral peak shift is 0.005 nm/K. However, for the Nd/Cr:YAG ceramic, the bandwidths are 1.2 and 1.9 nm in the case of 0.1% Cr ion doping and 3% Cr ion doping, respectively, owing to the existence of excited Cr ions and the shortening of the effective Nd ion coherence time. It is prospected that the laser medium can be used at a high temperature of 600 K.     

Tunable, μs-pulsed ytterbium fiber laser system with a linewidth below 2.7 GHz

We report on a widely tunable, pulsed laser system with narrow spectral linewidth based on a continuous wave ytterbium fiber oscillator, a pulse shaper and a power amplifier stage. The system is tunable from 1055 nm to 1085 nm and provides a maximum pulse energy of 155 μJ with a pulse duration of 1-5 μs. The linewidth is less than 2.7 GHz over the whole tuning range.     

Tunable double-clad ytterbium-doped fiber laser based on a double-pass Mach-Zehnder interferometer

We have demonstrated an adjustable double-clad Yb³⁺-doped fiber laser using a double-pass Mach-Zehnder interferometer. The laser is adjustable over a range of 40 nm from 1064 nm to 1104 nm. By adjusting the state of the polarization controller, which is placed in the double-pass Mach-Zehnder interferometer, we obtained central lasing wavelengths that can be accurately tuned with controllable spacing between different tunable wavelengths. The laser has a side mode suppression ratio of 42 dB, the 3 dB spectral width is less than 0.2 nm, and the slope efficiencies at 1068 nm, 1082 nm and 1098 nm are 23%, 32% and 26%, respectively. In addition, we have experimentally observed tunable multi-wavelengths lasing output.     

Photoluminescence and optical transmission of diamond and its imitators

Photoluminescence and optical transmission spectra of several samples of natural and synthetic diamond and its imitators - fianite and corundum - are investigated. The band-A of luminescence at 440 nm, the vibronic N3 system of luminescence and absorption at 415.2 nm, the fundamental absorption edge at 225 nm, and the secondary absorption below 308 nm are the main identifying markers of natural diamonds. For synthetic diamonds, however, such identifying markers are the free-exciton luminescence at 235 nm, the band-A, and the fundamental absorption edge. Fianites can be identified by the structureless wideband at 500 nm and the wide transmission band in the entire visible range. Colored corundum samples with chrome impurities emit the narrow line at 693 nm and show the absorption band in the 500-600 nm spectral range. A new method for diamond express identification is developed on the basis of measurement of photoluminescence and optical transmission spectra of the samples. It is shown that a diamond tester can be designed combining a spectrometer and a KrCl-excilamp radiating at 222 nm.     

Integrated photonic crystal spectrometers for sensing applications

A combination of negative refraction and diffraction compensation in a superprism-based photonic crystal structure is used to demonstrate a compact on-chip photonic crystal spectrometer. This structure provides strong dispersion and signal isolation, which are essential for forming an efficient and compact spectrometer. Performance of these spectrometers as spectral pattern detectors is discussed. The experimental results show that a PC structure with 80 μm × 220 μm dimension can locate a single spectral feature with better than 10 pm accuracy over a bandwidth of 50 nm around 1550 nm center wavelength at an output signal-to-noise ratio of 13 dB.     

Optical features of the gold nanoparticles deposited on ITO substrates

We have performed firstly studies of the photoinduced second order susceptibilities in the Au nanoparticles (NP) A, B and C under simultaneous influence of the bicolor 1064 nm and bicolor laser treatment (1064 nm 10 ns pulsed laser with pulse power densities 532 nm 10 ns laser treatment and the cw 300 mW 532 nm SHG coherent laser beams. We have studied three types of samples possessing irregular and different dense parameters of the Au NP deposited on the ITO substrate. We have found that the maximal bicolor (1064 nm and 532 nm) stimulated optical second harmonic generation for the 10 ns pulse duration was observed for the samples possessing irregular Au NP deposited on the ITO. We have performed studies of the photoinduced second order susceptibilities in the Au NP under simultaneous influence of the bicolor 1064 nm and bicolor laser treatment (1064 nm 10 ns pulsed laser with pulse power densities 532 nm 10 ns laser treatment and the cw 300 mW 532 nm SHG coherent laser beams). We have found that during the 15-20 min of the cw treatment there occur the principal changes in the absorption maxima. These maxima indicate on the occurrence of the additional absorption nearby the 308 nm and 310 nm and 345 nm spectral bands. The later are caused by the occurrence of the trapping levels in the border between the ITO substrate and the Au nanoparticles.     

Optimization of optical parametric chirped pulse amplification with different pump wavelengths

Optical parametric chirped pulse amplification with different pump wavelengths was investigated using LBO crystal, at signal central wavelength of 800 nm. According to our theoretical simulation, when pump wavelength is 492.5 nm, there is a maximal gain bandwidth of 190 nm centered at 805 nm in optimal noncollinear angle using LBO. Presently, pump wavelength of 492.5 nm can be obtained from second harmonic generation of a Yb:Sr₅(PO₄)₃F laser. The broad gain bandwidth can completely support ∼6 fs with a spectral centre of seed pulse at 800 nm. The deviation from optimal noncollinear angle can be compensated by accurately tuning crystal angle for phase matching. The gain spectrum with pump wavelength of 492.5 nm is much better than those with pump wavelengths of 400, 526.5 and 532 nm, at signal centre of 800 nm.     

Investigation of all-optical analog-to-digital quantization using a chalcogenide waveguide: A step towards on-chip analog-to-digital conversion

We have investigated all-optical analog-to-digital quantization by broadening the pulse spectrum in a chalcogenide (As₂S₃) waveguide and subsequently slicing the measured spectrum using an array of filters. Pulse spectral broadening was measured for 8 different power levels in a 6 cm long As₂S₃ waveguide and used to analyze an 8-level all-optical quantization scheme employing filters with full-width at half-maximum (FWHM) bandwidth of 2 nm. A supercontinuum spectrum with −15 dB spectral width up to 324 nm was observed experimentally at large powers. This large spectral broadening, combined with filtering using a 128 channel arrayed waveguide grating (AWG) with 2 nm filter spacing, has the potential for all-optical quantization with 7-bit resolution. In order to encode the quantized signal we propose an encoder scheme which can be implemented using optical Exclusive-OR gates. Demonstrating all-optical quantization using a planar waveguide is an important step towards realizing all-optical A/D conversion on a chip.     

Supercontinuum generation by combining clad-pumped Er/Yb co-doped fiber amplifier and highly nonlinear photonic crystal fiber

We present an experimental study on supercontinuum generation by combining a clad-pumped Er/Yb co-doped fiber amplifier (EYDFA) and a highly nonlinear photonic crystal fiber (HNL-PCF). By using the nonlinear polarization rotation technique, a stable femtosecond optical pulse seed signal with a central wavelength of 1556.36 nm and a spectral line width of ∼5.6 nm has been obtained. Then, this pulsed seed signal is amplified by the EYDFA, the amplified pulse, which, with the broaden spectrum, propagates in the HNL-PCF. The 20 dB bandwidth of ∼520 nm from 1230 to 1750 nm is obtained.     

2 W/nm peak-power all-fiber supercontinuum source and its application to the characterization of periodically poled non-linear crystals

We demonstrate a uniform high spectral brightness and peak power density all-fiber supercontinuum source. The source consists of a nanosecond Ytterbium fiber laser and an optimal length PCF producing a continuum with a peak power density of 2 W/nm and less than 5 dB of spectral variation between 590 and 1500 nm. The Watt level per nm peak power density enables the use of such sources for the characterization of non-linear materials. Application of the source is demonstrated with the characterization of several periodically poled crystals.     

Continuum generation in water and carbon tetrachloride using a picosecond Nd-YAG laser pulse

We have measured the continuum generated in two non-linear media, distilled water and carbon tetrachloride, pumped by a 36 ps Neodymium Yttrium Aluminium Garnet laser pulse operating at 1.06 μm. We show that the induced spectral broadening extends from 400 nm to 850 nm in both media. However, we find that continuum spectra of carbon tetrachloride exhibit an oscillatory structure with an energy range of about 445 cm⁻¹ which corresponds to the fundamental Raman component. This behaviour is due to a spectral non-overlapping of the Raman anti-Stokes components photoinduced in this medium.     

Improvement of optical sensing performances of a double-slot-waveguide-based ring resonator sensor on silicon-on-insulator platform

We demonstrate a label-free photonic biosensor with double slots based on micro-ring resonator. The footprint is less than 25 μm × 15 μm. Finite-difference time-domain (FDTD) method is used to analyze the influence of several key parameters on the performance of the double-slots micro-ring resonators. An asymmetric structure is considered for the ring waveguide in order to improve the sensor's bending efficiency. Our numerical analysis shows that the sensitivity of double-slot micro-ring resonator sensor with the radius of 5 μm reaches a value of 708 nm/RIU. The quality factor of 580 and the free spectral range (FSR) of 33 nm are achieved.     

Widely tunable sum-frequency generation in PPLN waveguide pumped by a multi-wavelength Yb-doped fiber laser

We present some experimental results on tunable sum-frequency generation in a periodically poled lithium-niobate waveguide using a multi-wavelength fiber laser pump stabilized by a nonlinear optical loop mirror. We are able to up-convert to about 629 nm a continuous-wave infrared signal varying from 1497 nm to 1525 nm. Such a wideband conversion efficiency is ensured by the multiple spectral components of the laser pump, which is controlled by an adjustable Fabry-Perot filter. Potential applications, in particular for stellar imaging, are discussed.     

Broadband photoluminescence from pulsed laser deposited Er2O3 films

Photoluminescence (PL) with the bandwidth of 45 nm (1523-1568 nm at the level of 3 dB) was observed in amorphous Er₂O₃ films grown on to the quartz substrate by pulsed laser ablation of erbium oxide stoichiometric target. Optical transmission spectrum has been fitted to Swanepoel formula to determine the dispersion of refractive index and to extract resonance absorption peaks at 980 and 1535 nm. The maximum gain coefficient of 800 dB/cm at 1535 nm was estimated using McCumber theory and experimental spectrum of the resonance absorption. In 5.7 mm-long waveguide amplifier a theory predicts the spectral gain of 20 dB with 1.4 dB peak-to-peak flatness in the bandwidth of 31 nm (1532-1563 nm) when 73% of Er³⁺ ions are excited from the ground state to the ⁴I_13/2 laser level. Strong broadband PL at room temperature and inherently flat spectral gain promise Er₂O₃ films for ultra-short high-gain optical waveguide amplifiers and integrated light circuits.     

Multichannel silicon WDM ring filters fabricated with DUV lithography

We have fabricated 9-channel silicon wavelength-division-multiplexing (WDM) ring filters using 193 nm deep-ultraviolet (DUV) lithography and investigated the spectral properties of the ring filters by comparing the transmission spectra with and without an upper cladding. The average channel-spacing of the 9-channel WDM ring filter with a polymeric upper cladding is measured about 1.86 nm with the standard deviation of the channel-spacing about 0.34 nm. The channel crosstalk is about −30 dB, and the minimal drop loss is about 2 dB.     

White-light emission derived from yttrium tungstate-chloride xerogel without activator ions

White xerogel powder of yttrium tungstate-chloride was synthesized, and its photoluminescence properties were investigated. Under the excitation of 254 nm, the xerogel phosphor exhibits emission ranging from 300 to 650 nm. This luminescent spectrum is identified as two emission bands of 300-400 and 400-650 nm due to different emission mechanism. While the emission band of 300-400 nm is ascribed to the charge transfer (CT) from O to metal W, the emission of 400-650 nm is attributed to electron-hole (e⁻-h⁺) carrier emission related to oxygen vacancies. By calcining the sample in reducing atmosphere, the number of oxygen vacancies acting as luminescence centers is increased. As a result, the emission intensity of 400-650 nm is significantly enhanced. Based on electron paramagnetic resonance and spectral analysis, the mechanism of peroxy-radical hole traps (PRHT) is proposed for the luminescence of 400-650 nm.