Narrow Spectral Width Research Articles

파라핀이 코팅된 Rb 증기 셀에서 비선형 광자기 효과 신호

본 연구에서는 파라핀이 코팅된 Rb원자 증기 셀을 이용하여 <TEX>$^{87}Rb$</TEX> <TEX>$D_1$</TEX>전이선의 Hanle스펙트럼과 비선형 광자기 효과 신호를 조사하였다. 파라핀 코팅 증기 셀의 효과에 의한 좁은 스펙트럼 폭을 가진 영역과 순수 증기 셀에서 얻을 수 있는 넓은 스펙트럼폭을 가진 이중구조의 Hanle 스펙트럼을 관측할 수 있었다. 스펙트럼에 나타난 이중구조에서 좁은 선폭 영역의 선폭은 1 kHz로 측정되었고, 스펙트럼 크기는 전체 스펙트럼에 대해서 10%로 측정되었다. 또한, Hanle 스펙트럼에 대응되는 이중 미분형태의 비선형 광자기 신호를 관측하였으며, 기울기가 급격하게 변하는 비선형 광자기 신호의 기울기는 레이저의 출력이 <TEX>$200{\mu}W$</TEX>일 때 대략 10 mV/<TEX>${\mu}T$</TEX>였다. In our study, the Hanle spectrum and nonlinear magneto-optic effect (NMOE) signals were observed as a function of magnetic field on <TEX>$D_1$</TEX> line of <TEX>$^{87}Rb$</TEX> atoms contained in a paraffin coated vapor cell. We observed the double structure from the Hanle and the NMOE spectrum in the paraffin coated Rb vapor cell. The narrow spectral width of the narrow resonance signal is approximately 1 kHz and the magnitude is approximately 10 percent of the total spectrum. Also, the NMOE signals corresponding to the Hanle configuration consisted of two different dispersion-like features. At the near zero magnetic field, a sharp slope signal was centered, and its value was 10 mV/<TEX>${\mu}T$</TEX> with laser power was <TEX>$200{\mu}W$</TEX>.

Multi-wavelength generation of an extremely narrow pulse using a ring resonator system for bio-cells microscopy

We propose a new system of an extremely narrow light pulse generation for optical microscopy applications using a nonlinear ring resonator system. The system consists of one nano and three micro-optical ring resonators, which can be used to generate the 50 fm (10 −15 m) optical spectral width at the broad wavelength spectrum. By using a soliton pulse with a pulse width of 50 ps, peak power of 1 W, center wavelength at 550 nm, and after the soliton pulse is launched into the first ring device, the chaotic pulses are generated within the first ring. The chaotic filtering behaviors are performed by using the second and the third ring devices, whereas the extremely short pulse, i.e. narrow spectral width, can be generated by using the extended nano-ring device. The broad spectrum of the harmonic waves is generated and filtered, which is of use in optical tomography. Results obtained have shown that the generation of the broad spectrum of short pulse with width 100 fm and peak power 60 mW is achieved. The possibility of using such a system for nondestructive bio-cells microscopy, for visualizing bio-cells and for bio-cells tomography is also discussed in detail.

Scanning tunneling microscope light emission spectra of polycrystalline [formula omitted] and [formula omitted

We have observed scanning tunneling microscope light emission (STM-LE) spectra of Ge 2Sb 2Te 5 and Sb 2Te 3. Although these chalcogenide alloys exhibit band gaps less than 0.5 eV, the STM-LE was observed with a narrow spectral width at a photon energy of 1.5 eV for both materials. By analyzing its bias voltage, polarity, and temperature dependencies combined with recently reported theoretical electronic structures, we concluded that the STM-LE is excited by electronic transitions taking place in the local electronic structure having a direct gap-like shape with a band gap of 1.5 eV, commonly found in the electronic structures of both materials.

An extremely narrow UV pulse generation using a micro- and nano-ring system for pico-lithographic resolution

We propose a new technique of an extremely narrow ultraviolet (UV) pulse width generation for pico-lithography technology using a nonlinear ring resonator system. A system consists of three micro- and a nano-optical ring resonators, which can be used to generate the 50 pm (10 −12 m) optical spectral width at the ultraviolet wavelength. By using a soliton pulse with a pulse width of 50 ns, 1 W peak power, center wavelength at 1550 nm, after the soliton pulse is launched into a first ring device, the chaotic pulses are generated within the first ring. The chaotic filtering behaviors are performed by using the second and third ring devices, whereas the extremely short pulse, i.e. narrow spectral width, can be generated by using the extended nano-ring device. The broad spectrum of the harmonic waves is generated and filtered, especially the generation of third harmonic wave, which is known as the ultraviolet wavelength, is achieved, which is capable of forming pico-lithographic resolution. Results obtained have shown that the generation of the spectral width of 50 pm at a wavelength of 511.125 nm, with peak power at 35 mW is achieved.

808 nm broad area DFB laser for solid-state laser pumping application

Wavelength stabilised 808 nm broad area distributed feedback (DFB) diode lasers with high continuous-wave (CW) output have been realised. The centre wavelength was locked at the Bragg condition with narrow spectral widths of 0.3 nm FWHM and shifted at a rate of 0.062 nm/degC. The 2 mm long laser showed a record high 57 wall-plug efficiency and more than 4W CW output power at 25 C heatsink temperature. It is an ideal source for pumping solid-state lasers such as Nd-doped YAG and YVO 4 .

LONG RANGE SURFACE PLASMON DEVICES DESIGN USING SUBWAVELENGTH METAL GRATING

In this paper we review a new electro-optic devices design strategy using long range surface plasmon (LRSP) excitation along subwavelength metal grating. It is shown that LRSP can be excited on extremely thin subwavelength metal grating embedded in symmetric dielectric ambient. Due to coupling and propagation of LRSP between the metal grating nanowires, a super-narrow reflection dip can be obtained. Compared with conventional LRSP along metal thin film, much narrower resonance is achieved through decreased damping from the existence of large dielectric gaps between the grating nanowires. This interesting phenomenon can be used to design electro-optics devices with improved performance. Examples of electro-optic modulator design with lower insertion loss and low operating voltage and spectral notch filter design with very narrow spectral width will be shown. Its application in refractive index sensing is also discussed.

Examination of Chlorin–Bacteriochlorin Energy‐transfer Dyads as Prototypes for Near‐infrared Molecular Imaging Probes†

New classes of synthetic chlorin and bacteriochlorin macrocycles are characterized by narrow spectral widths, tunable absorption and fluorescence features across the red and near-infrared (NIR) regions, tunable excited-state lifetimes (<1 to >10 ns) and chemical stability. Such properties make dyad constructs based on synthetic chlorin and bacteriochlorin units intriguing candidates for the development of NIR molecular imaging probes. In this study, two such dyads (FbC-FbB and ZnC-FbB) were investigated. The dyads contain either a free base (Fb) or zinc (Zn) chlorin (C) as the energy donor and a free base bacteriochlorin (B) as the energy acceptor. In both constructs, energy transfer from the chlorin to bacteriochlorin occurs with a rate constant of approximately (5 ps)(-1) and a yield of >99%. Thus, each dyad effectively behaves as a single chromophore with an exceptionally large Stokes shift (85 nm for FbC-FbB and 110 nm for ZnC-FbB) between the red-region absorption of the chlorin and the NIR fluorescence of the bacteriochlorin (lambda(f) = 760 nm, Phi(f) = 0.19, tau approximately 5.5 ns in toluene). The long-wavelength transitions (absorption, emission) of each constituent of each dyad exhibit narrow (<or=20 nm) spectral widths. The narrow spectral widths enabled excellent selectivity in excitation and detection of one chlorin-bacteriochlorin energy-transfer dyad in the presence of the other upon diffuse optical tomography of solution-phase phantoms.

Measurement of Facet Reflectivity Through Reflection Gain in Fabry–PÉrot Laser Diode

We propose a simple and useful method to measure the facet reflectivity in a Fabry-Perot laser diode (LD). The new measurement method does not require information on LD parameters such as threshold current or optical spectrum. The measurement is based on a simple formula that describes the relationship of facet reflectivity and reflection gain with launching the probe beam of a narrow spectral width.

A new protein A assay based on Raman reporter labeled immunogold nanoparticles

A unique, sensitive, highly specific, and photobleaching-resistant immunoassay system utilizing gold nanoparticles and surface-enhanced Raman scattering (SERS) is described. This new system, featuring a capability of bifunctional analysis, is manufactured by chemisorption of antibody immunoglobulin G (IgG) on gold nanoparticles (AuNP), followed by coupling the Raman-active reporter molecule, 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB) to the surface of IgG–AuNP. The adsorbed DTNB molecules exhibit strong Raman signals via both electromagnetic and chemical enhancement. The narrow spectral widths and high photostability assure the system to be an excellent detection label. This SERS-based immunoassay is applied to the detection of protein A, which is a specific surface antigen of Staphylococcus aureus. A working curve is obtained by plotting the intensity of the SERS signal of symmetric NO2 stretching of DTNB at 1333cm−1 versus the concentration of the analyte (antigen). A dynamic range of two to three orders of magnitude and a detection limit of 1pg/mL of protein A are achieved.

New strategy for band-gap tuning in semiconductor nanocrystals

In the last decade, the main efforts have focused on the preparation of different sized binary II–VI group semiconductor nanocrystals to obtain different color-emitting luminescence. However, the tuning of physical and chemical properties by changing the particle size could cause problems in many applications, in particular if unstable small particles are used. Recent advances have led to the exploration of tunable optical properties by changing their constituent stoichiometries in ternary alloy nanocrystals. High-quality Zn x Cd1−x Se alloy nanocrystals have been successfully prepared at high temperature by incorporating stoichiometric amounts of Zn and Se into pre-prepared CdSe nanocrystals or embryonic CdSe nuclei. With increasing Zn content, a composition-tunable emission across the whole visible spectrum has been demonstrated by a systematic blue-shift in emission wavelength. High-quality alloy Zn x Cd1−x S nanocrystals have been obtained by the conucleation and co-growth of the constituents through the reaction of a mixture of CdO- and ZnO-oleic acid complexes with sulfur at elevated temperatures. The obtained Zn x Cd1−x S alloy nanocrystals possess superior optical properties with photoluminescence quantum yields of 25–50%, especially the extremely narrow emission spectral width (fwhm=14 nm).

High-average-power light source below 200 nm from a KBe_2BO_3F_2 prism-coupled device

Using a 2.3 mm thick KBe(2)BO(3)F(2) crystal optically contacted with CaF(2) in a prism-coupled device, we have obtained an average output power of as much as 360 mW at 200 nm. Long-term stability was verified above a 150 mW level at 200 nm. An output power of 50 mW was also obtained with a narrow spectral width of 0.007 pm at 193.5 nm.

Hydrogen analysis in solid samples by utilizing He metastable atoms induced by TEA CO 2 laser plasma in He gas at 1 atm

A TEA CO 2 laser (350 mJ–1.5 J, 10.6 μm, 200 ns, 10 Hz) was focused onto a metal sub-target under He as host gas at 1 atmospheric pressure with a small amount of impurity gas, such as water and ethanol vapors. It was found that the TEA CO 2 laser with the help of the metal sub-target is favorable for generating a strong, large volume helium gas breakdown plasma at 1 atmospheric pressure, in which the helium metastable-excited state was then produced overwhelmingly. While the metal sub-target itself was never ablated. The helium metastable-excited state produced after the strong helium gas breakdown plasma was considered to play an important role in exciting the atoms. This was confirmed by the specific characteristics of the detected Hα emission, namely the strong intensity with low background, narrow spectral width, and the long lifetime. This technique can be used for gas and solid samples analysis. For nonmetal solid analysis, a metal mesh was introduced in front of the nonmetal sample surface to help initiation of the helium gas breakdown plasma. For metal sample, analysis can be carried out by combining the TEA CO 2 laser and an Nd–YAG laser where the Nd–YAG laser is used to ablate the metal sample. The ablated atoms from the metal sample are then sent into the region of helium gas breakdown plasma induced by the TEA CO 2 laser to be excited through the helium metastable-excited state. This technique can be extended to the analysis of other elements, not limited only to hydrogen, such as halogens.

Light Emission from Porous Silicon Photoetched in Aqueous Alkali Salt Solutions

An interband-transition model was applied to explain the emission mechanism in porous silicon (PSi) fabricated by photoetching in aqueous HF and salt (NaF and KF) solutions. The HF-formed samples show a yellow photoluminescence band at ∼2 eV. The salt-formed samples, on the other hand, show an ultraviolet (UV) emission peak at ∼3.3 eV with a spectral width of ∼0.1 eV, together with a broad emission band at ∼2.7 eV. The broad emission bands at ∼2 and ∼2.7 eV can be explained by the quantum-mechanical confinement effect, i.e., a relaxation of the momentum conservation at and above the indirect-absorption edge (supra-EgID emission). This effect may also lead to a change in the E1 critical point (CP) from the two-dimensional M0 to the zero-dimensional CP with decreasing nanocrystalline size. The change in the E1-CP dimensionality makes possible an emission in the UV region with a narrow spectral width.

An experimental investigation of the optical switching characteristics using an optical Sagnac interferometer incorporating one and two ring resonators

We present the use of a fiber optic Sagnac interferometer incorporating one and two fiber optic ring resonators to characterize experimentally the optical switching behaviors. These prototypes were formed by the Sagnac interferometer and serially connected to the ring resonators. The input optical signal was launched via one end of the interferometer, where the polarization control was employed to obtain the maximum optical transmission power. Results obtained have shown that the increasing in switching time (i.e. narrower spectral width) and power can be achieved.

The Marine Stratus/Stratocumulus Experiment (MASE): Aerosol‐cloud relationships in marine stratocumulus

The Marine Stratus/Stratocumulus Experiment (MASE) field campaign was undertaken in July 2005 off the coast of Monterey, California to evaluate aerosol‐cloud relationships in the climatically important regime of eastern Pacific marine stratocumulus. Aerosol and cloud properties were measured onboard the Center for Interdisciplinary Remotely‐Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft. One cloud that was clearly impacted by ship emissions as well as the ensemble of clouds observed over the entire mission are analyzed in detail. Results at both the individual and ensemble scales clearly confirm the Twomey effect (first indirect effect of aerosols) and demonstrate drizzle suppression at elevated aerosol number concentration. For the ship track impacted cloud, suppressed drizzle in the track led to a larger cloud liquid water path (LWP) at the same cloud thickness, in accord with the so‐called second indirect effect. Ensemble averages over all clouds sampled over the entire 13‐flight mission show the opposite effect of aerosol number concentration on LWP, presumably the result of other dynamic influences (e.g., updraft velocity and ambient sounding profile). Individual polluted clouds were found to exhibit a narrower cloud drop spectral width in accord with theoretical prediction (M.‐L. Lu and J. H. Seinfeld, Effect of aerosol number concentration on cloud droplet dispersion: A large‐eddy simulation study and implications for aerosol indirect forcing, Journal of Geophysical Research, 2006). This field experiment demonstrates both the indirect aerosol effect on ship track perturbed clouds, as well as the subtleties involved in extracting these effects over an ensemble of clouds sampled over a 1‐month period.

Strong photoluminescence at 1.3μm with a narrow linewidth from nitridized InAs∕GaAs quantum dots

Nitridized quantum dots (QDs) were prepared by metal-organic chemical vapor deposition. These QDs all showed strong photoluminescence (PL) emission at 1.3μm at room temperature, narrow spectral widths of 30meV, and large separations of 98meV between the ground and first excited states. Interestingly, the PL peak positions of the nitridized QDs were all around 1.3μm, despite the QDs having been prepared using significantly different amounts of nitrogen. Time-resolved PL revealed no electronic coupling between the QDs. These properties could potentially make these nitridized QDs very useful candidates for the fabrication of devices emitting at 1.3μm.

Hydrogen and Deuterium Analysis Using Laser‐Induced Plasma Spectroscopy

Hydrogen emission in laser plasma has been studied by focusing a TEA CO2 laser and Nd‐YAG lasers on various types of samples, such as glass, quartz, and zircaloy pipes doped with hydrogen. It was found that Hα emission with a narrow spectral width occurs with high efficiency when the laser plasma is produced in low‐pressure host gas. In contrast, the conventional well‐known laser‐induced breakdown spectroscopy (LIBS), which operates at atmospheric air pressure, cannot be applied for the analysis of hydrogen as impurity. The specific characteristic of hydrogen emission in low‐pressure plasma is interpreted on the basis of our shock wave model, taking account of the fact that the hydrogen mass is extremely light compared to that of the host target. Another experimental study on gas analysis was conducted using an Nd‐YAG laser and helium host gas at atmospheric pressure on a sample of mixed water (H2O) and heavy water (D2O) in vapor form. It was shown that completely resolved hydrogen (Hα) and deuterium (Dα) emission lines that are separated by only 0.179 nm could be obtained at a properly delayed detection time when the charged particles responsible for the strong Stark broadening effect in the plasma have mostly disappeared. It is argued that a helium metastable excited state plays the important role in the hydrogen excitation process.

53% wallplug efficiency 975 nm distributed feedback broad area laser

100 µm-stripe, 2 mm-long, DFB diode lasers with narrow spectral widths of 2.3 Å FWHM were achieved at a CW power of 5 W. The centre wavelength was locked at the Bragg condition and shifts at a rate of 0.065 nm K−1. 1 mm-long DFB laser showed a record high 53% wallplug efficiency for grating-stabilised semiconductor lasers at 25°C heatsink temperature and 2 W CW output power.

Retrieval of Arbitrarily Shaped Raindrop Size Distributions from Wind Profiler Measurements

Abstract An efficient iterative retrieval method for arbitrarily shaped raindrop size distributions (ITRAN) is developed for Doppler spectra measured with a wind profiler. A measured Doppler spectrum is a convolution of the precipitation spectrum and the turbulent spectrum. Deconvolution of the Doppler spectra is achieved through repeated convolutions. The developed method assumes no prior shape of drop size distributions and automatically obtains raindrop size distributions; additionally, it can be applied to large data volumes. Furthermore, it is insensitive to initial values. The method was applied to both simulated and observed spectra. Derived drop size distributions agree with simulated values. Narrower turbulent spectral widths yield better results. Integral values of median volume diameter (D0), liquid water content (LWC), and radar reflectivity factor are estimated with errors of less than 10%. Accurate vertical profiles of raindrop size distributions result when this method is applied to wind profiler data. The technique performed very well with most observed spectra. Some recovered spectra departed from the corresponding measured spectra, for cases in which a clear-air peak could not be accurately reproduced because of uncertainties in the location of the minimum position between the clear-air echo and the precipitation echo. Statistical relationships between LWC and integral rainfall parameters yield interesting features. The median volume diameter is statistically independent of the LWC and is associated with the large variability of the total number of drops, NT, between events. Vertical profiles from one event show a clear inverse relationship between NT and D0

High-energy saturable absorber mode-locked fiber laser system

We demonstrate a mode-locked erbium-doped fiber laser with a 1-microm InGaAs saturable absorber that produces 84-ps, 1-nJ transform-limited pulses. Measurements of the InGaAs multiple quantum well revealed a slow saturable absorber that is useful for passive mode locking. Optical fiber was added to extend the cavity and vary the repetition rate from 51 kHz to 5.4 MHz. The narrow spectral width of the laser output (<0.04 nm) permits amplification to 0.2 microJ/pulse with minimal pulse broadening. Pulse energies as large as 1.7 microJ can be achieved with pulse widths of <330 ps. Average powers of 0.5 W at megahertz repetition rates are demonstrated.