Precise Wavelength Research Articles

Compact soft x-ray spectrometer for plasma diagnostics at the Heidelberg Electron Beam Ion Trap

A compact flat-field soft x-ray grazing-incidence grating spectrometer equipped with a cryogenically cooled back-illuminated charge-coupled device camera was built and implemented at the Heidelberg Electron Beam Ion Trap. The instrument spans the spectral region from 1 to 37 nm using two different gratings. In slitless operation mode, it directly images a radiation source, in this case ions confined in an electron beam ion trap, with high efficiency and reaching hereby a resolving power of lambda/Deltalambda approximately =130 at 2 nm and of lambda/Deltalambda approximately =600 at 28 nm. Capable of automatized operation, its low noise and excellent stability make it an ideal instrument not only for spectroscopic diagnostics requiring wide spectral coverage but also for precision wavelength measurements.

CHIP-SIZE WAVELENGTH DETECTORS

Chip-size wavelength detectors are described that can resolve the spectrum of the incident light with high accuracy over a broad spectral range. The devices can be configured either as compact spectrometers or precise wavelength shift detectors. Applications that are anticipated to benefit from the spectrometers include reagentless optical identification of analytes in fluidic and aerosol samples. The wavelength shift detector is widely applicable as read-out instrument for optical sensors in which a stimulus (e.g., temperature, strain, PH-value, etc.) results in a wavelength shift of an optical output signal, examples include the interrogation system for Fiber Bragg Grating sensors, photonic crystal sensors, Fabry-Perot type sensors, and sensors in which an analyte influences a laser cavity and thereby its emission wavelength.

Testing QED Screening and Two-Loop Contributions with He-Like Ions

We report wavelength measurements of H-like and He-like ions obtained with a novel x-ray spectrometer at the Heidelberg Electron Beam Ion Trap. The experimental uncertainty for the Lyman-alpha1 wavelength in Cl16+ is reduced by a factor of 3 and, as expected, excellent agreement with theory is maintained. For the resonance line in He-like Ar16+, an uncertainty of only deltalambda/lambda=2x10(-6) was achieved. This is the most precise x-ray wavelength reported for highly charged ions to date, and allows to test recent predictions on QED two-electron and two-photon radiative corrections for He-like ions. The results also point to the advantages of establishing absolute x-ray wavelength standards using Lyman-alpha transitions (in the present case Ar17+ Lyman-alpha1) to supersede the current ones.

High-precision wavelength calibration of astronomical spectrographs with laser frequency combs

We describe a possible new technique for precise wavelength calibration of high-resolution astronomical spectrographs using femtosecond-pulsed mode-locked lasers controlled by stable oscillators such as atomic clocks. Such ‘frequency combs’ provide a series of narrow modes which are uniformly spaced according to the laser's pulse repetition rate and whose absolute frequencies are known a priori with relative precision better than 10−12. Simulations of frequency comb spectra show that the photon-limited wavelength calibration precision achievable with existing echelle spectrographs should be ∼1 cm s−1 when integrated over a 4000 Å range. Moreover, comb spectra may be used to accurately characterize distortions of the wavelength scale introduced by the spectrograph and detector system. The simulations show that frequency combs with pulse repetition rates of 5–30 GHz are required, given the typical resolving power of existing and possible future echelle spectrographs. Achieving such high repetition rates, together with the desire to produce all comb modes with uniform intensity over the entire optical range, represents the only significant challenges in the design of a practical system. Frequency comb systems may remove wavelength calibration uncertainties from all practical spectroscopic experiments, even those combining data from different telescopes over many decades.

Focus on lasers and optics

Focus on lasers and optics

Flat Frequency Comb Generation With an Integrated Dual-Parallel Modulator

A dual-parallel Mach-Zehnder modulator is employed to generate an optical frequency comb. Flat spectral response is obtained by optimizing the dc bias and the RF drive parameters of the device which is driven in the gigahertz frequency range. We demonstrate theoretically and experimentally, a flat spectral output across nine sidebands. A tunable multiwavelength source based on this approach allows for very precise wavelength spacing for dense wavelength-division-multiplexing applications and has the advantages of efficiency and simplicity.

Closed-loop wavelength stabilization of an optical parametric oscillator as a front end of a high-power iodine laser chain

We present a complex stabilization and control system for a commercially available optical parametric oscillator. The system is able to stabilize the oscillator's output wavelength at a narrow spectral line of atomic iodine with subpicometer precision, allowing utilization of this solid-state parametric oscillator as a front end of a high-power photodissociation laser chain formed by iodine gas amplifiers. In such setup, a precise wavelength matching between the front end and the amplifier chain is necessary due to extremely narrow spectral lines of the gaseous iodine (approximately 20 pm). The system is based on a personal computer, a heated iodine cell, and a few other low-cost components. It automatically identifies the proper peak within the iodine absorption spectrum, and then keeps the oscillator tuned to this peak with high precision and reliability. The use of the solid-state oscillator as the front end allows us to use the whole iodine laser system as a pump laser for the optical parametric chirped pulse amplification, as it enables precise time synchronization with a signal Ti:sapphire laser.

The initial processing of the gas electron diffraction data: New method for simultaneous determination of the sector function and electron wavelength from gas standard data

The accuracy of the routine investigations by the modern gas-phase electron diffraction method is no more than 0.1%. The full error of parameters determination consists of several contributions including the scale error and the errors in sector function. For correction of the scale error and estimation of the sector function, the gas standard method is used in gas electron diffraction. We have developed the new method for simultaneous determination of the electron wavelength and the sector function from the intensity curves of the gas standards. The new method allows to achieve the electron wavelength precision of about 0.02–0.05%. The distinguishing feature of the new method is the use of several intensity curves for determination of the sector function, resulting in an increase of the reliability of the sector function determination. The additional information from alternative determinations of sector function can be also used for regularization.

Accurate wavelength calibration in the near-infrared for multielement analysis without the need for reference spectra

A new technique has been developed for an instant, precise, and accurate wavelength calibration over a wide pixel array for simultaneous, multielement spectral analysis based on an inverse numerical solution to the grating dispersion function. This technique is applicable to multielement analytical applications such as laser-induced breakdown spectroscopy (LIBS), particularly when using high-density gratings in the upper visible and in the near-infrared, where nonmetallic elements are detected. This application overcomes the need to use reference spectra for each window of observation and is tested on a commercially available LIBS instrument.

The EU BIOXHIT standard test crystal – verfiying Se-MAD beamlines

The standard test crystal is designed to provide an automated, fast and robust procedure for identifying potential problems in the complex hardware and software infrastructure of modern protein crystallographic (PX) synchrotron beamlines. The resulting diagnostics should be independent of the data integration software employed (XDS, MOSFLM/SCALA and HKL2000). The cubic form of bovine insulin (space group I213) has proved to be a good first choice for a test crystal, with high reproducibility in crystal growth and freezing, high symmetry for highly redundant data collection, there is an additional need to verify the operation of MAD beamlines, in particular those used for phasing of selenomethionine derivatives. For this purpose we have synthesised an organoselenium compound that crystallises in the suitable space group P41212 and has four selenium atoms in general positions in the asymmetric unit. We have determined precise cell dimensions at various temperatures by X-ray powder diffraction to test the possibility that the cell can be reproduced well enough to provide a precise wavelength calibration for MAD beamlines. We will present our experiences with the new Se-MAD test crystal. We are grateful to the EU for support (LHSG-CT-2003503420) and to the other BIOXHIT partners for the fruitful collaboration. m06.o01

Picosecond excitation energy relaxation processes in a ladder-type π-conjugated polymer

We studied the relaxation dynamics of excitations in the lowest electronically excited singlet state in a ladder-type π-conjugated polymer employing picosecond time-resolved spectroscopy with high spectral resolution. At 1.5 K both the decay dynamics and the rising component of the fluorescence transients from the low-energy tail of the distribution of excited states show a strong dependence on time and on the precise emission wavelength. At room temperature, in contrast, such dependencies are not observed. Finally, the data allow us to retrieve the radiative lifetime of the excited states both at 1.5 K and 296 K.

Spectral Variability of Quasars in the Sloan Digital Sky Survey. I. Wavelength Dependence

SDSS repeat spectroscopic observations have resulted in multiepoch spectroscopy for ~2500 quasars observed more than 50 days apart. From this sample, calibrating against stars observed simultaneously, we identify 315 quasars that have varied significantly between observations (with respect to assumed nonvariable stars observed concurrently). These variable quasars range in redshift from 0.5 to 4.72. This is the first large quasar sample studied spectroscopically for variability and represents a potentially useful sample for future high-redshift reverberation mapping studies. This also marks the first time the precise wavelength dependence of quasar variability has been determined, allowing both the continuum and emission-line variability to be studied. We create an ensemble difference spectrum (bright phase minus faint phase) covering rest-frame wavelengths from 1000 to 6000 Å. This average difference spectrum is bluer than the average single-epoch quasar spectrum; a power-law fit to the difference spectrum yields a spectral index αλ = -2.00, compared to an index of αλ = -1.35 for the single-epoch spectrum. This confirms that quasar continua are bluer when brighter. The difference spectrum also exhibits very weak or absent emission-line features; the strongest emission lines vary only 30% as much as the continuum. This small emission-line variability with respect to the continuum is consistent with the intrinsic Baldwin effect. Due to the lack of variability of the lines, measured photometric color is not always bluer in brighter phases but depends on redshift and the filters used. Lastly, the difference spectrum is bluer than the ensemble quasar spectrum only for λrest < 2500 Å, indicating that the variability cannot result from a simple scaling of the average quasar spectrum.

New FTS measurements, optimized energy levels and refined VUV standards in the Ne III spectrum

All observed spectral lines of Ne III in the range 204 A to 36 μm (277 cm-1 to 490000 cm-1) have been compiled and critically evaluated. 57 visible and ultraviolet lines of Ne III have been precisely measured using Fourier transform spectroscopy. An optimized level scheme has been derived from the total list of observed lines. Relative positions of about 180 out of a total of 226 previously known energy levels of Ne III have been determined with improved accuracy compared to previous studies. Excitation energies of almost all excited levels have been revised by (1.5–2.0) cm-1. 127 precise wavelength standards in the region 210 A to 2900 A have been derived. Concepts of error current and covariance matrix have been implemented in a computational algorithm that permits one to derive the uncertainties of Ritz wavelength standards obtained from a set of least-squares-optimized energy levels. Nine new energy levels have been found, and 16 new transitions have been identified in the extreme ultraviolet region. The ionization potential has been increased by 4.5 cm-1. The new value is (\(\rm 511543.5\pm 2.7)~cm^{-1}\) (\(\rm 63.4233~eV \pm 0.0003~eV\)).

In situdetection of the temporal and initial phase of the second harmonic of a microwave field via incoherent fluorescence

Measuring the amplitude and absolute (i.e., temporal and initial) phase of a monochromatic microwave field at a specific point of space and time has many potential applications, including precise qubit rotations and wavelength quantum teleportation. Here we show how such a measurement can indeed be made using resonant atomic probes via detection of incoherent fluorescence induced by a laser beam. This measurement is possible due to self-interference effects between the positive- and negative-frequency components of the field. In effect, the small cluster of atoms here act as a highly localized pickup coil, and the fluorescence channel acts as a transmission line.

Quantum Dots Protected with Tiopronin: A New Fluorescence System for Cell‐Biology Studies

Nanocrystals of semiconducting materials, otherwise included in the term quantum dots (QDs), have fascinated physicists, chemists and electronic engineers since the 1970s. The most striking feature of these materials is that their chemical and physical properties differ markedly from those of the bulk solid.[1] Since their quantum size effects are understood, fundamental and applied research on these systems has become increasingly popular. One of the most interesting applications is the use of nanocrystals as luminescent labels for biological systems.[2-5] The quantum dots have several advantages over conventional fluorescent dyes: they emit light at a variety of precise wavelengths depending on their size and have long fluorescent lifetimes

A wavelength-tunable optical transmitter using semiconductor optical amplifiers and an optical tunable filter for metro/access DWDM applications

This paper proposes and demonstrates a widely tunable and precisely controllable optical transmitter that uses semiconductor optical amplifiers (SOAs) and an optical tunable filter (OTF) for metro/access dense-wavelength-division-multiplexing (DWDM) systems/networks. The transmitter consists of a fiber-ring-laser section based on SOA(s) and an OTF and a modulation section based on an SOA. First, the requirements imposed on the components intended for the fiber-ring laser are clarified through approximate analyses and basic experiments. To obtain low-noise characteristics, the lower limit of effective OTF bandwidth is investigated by considering the SOA carrier lifetime. For obtaining wavelength precision, the upper limit of the effective OTF bandwidth is derived by considering the SOA ripple effect. Next, the proposed transmitter is demonstrated, where all SOAs are integrated into one planar lightwave circuit (PLC) platform using spot-size converting technology. By designing the fiber-ring-laser section according to the clarified requirements, a wavelength control precision of /spl plusmn/1.75GHz is achieved while realizing the required relative intensity noise (RIN) from 1540 to 1560 nm. Finally, it is demonstrated that the transmitter can handle signals at up to 1.25 Gb/s.

Broadband precision wavelength meter based on a stepping Fabry–Pérot interferometer

We have constructed a broadband apparatus for wavelength metrology capable of absolute accuracy at a level of better than 2 parts in 109. An evacuated plane-parallel Fabry–Pérot interferometer with continuously adjustable mirror separation is used to compare the wavelength of a single-frequency tunable laser with that of an iodine-stabilized HeNe laser used as a wavelength standard. This work details apparatus construction, a thorough investigation of systematic errors, and data analysis. The wavelengths of five Doppler-free Te2130 transitions in the region from 475.6 to 490.8 nm have been measured and are found to be in excellent agreement with previous measurements. In addition, the wavelengths of five previously unmeasured Te2130 transitions spanning the region from 424.9 to 462.3 nm have been determined for use as new reference wavelength standards.

광학부품의 진공자외선특성 측정용 분광반사율계 제작

진공자외선 파장영역에서 광학부품의 분광특성을 측정할 수 있는 중수소광원과 진공단색화장치, 시료챔버 및 광 검출기 구조의 진공자외선 분광반사율계를 제작하였다. 제작된 진공자외선 분광반사율계는 115nm∼330 nm의 분광영역에서 약 3.0<TEX>${\times}$</TEX><TEX>$10^{-4}$</TEX> Pa의 기압에서 작동하였다. 253.652 nm와 184.95 nm의 수은 선스펙트럼으로 진공단색화장치의 파장을 교정하여 그 분해능이 0.012 nm이고, 파장정확도가 <TEX>$\pm$</TEX>0.03 nm 임을 확인하였다. 중수소 광원을 이용하여 115 nm∼230 nm 파장대역의 진공자외선 영역에서 여러 가지 광학부품들에 이용되고 있는 재료(MgF<TEX>$_2$</TEX>, CaF<TEX>$_2$</TEX>, BaF<TEX>$_2$</TEX>, SiO<TEX>$_2$</TEX>, Sapphire)들의 분광투과율과 반사율을 측정하였다. We fabricated a vacuum ultraviolet spectre-reflectometer which consists of a deuterium light source, a vacuum monochromator, and a sample chamber and detector module. The operation was performed in the ultraviolet spectral ranges between 115 nm and 330 nm at the vacuum pressure of 3.0 <TEX>${\times}$</TEX> 10<TEX>$^{-4}$</TEX> Pa. The wavelength of the vacuum monochromator was calibrated with the line spectrum of a low pressure Mercury lamp of 253.652 nm and 184.95 nm wavelengths, and its resolution was 0.012 nm, and the precision of wavelength was <TEX>$\pm$</TEX> 0.03 nm. With this reflectometer and a deuterium lamp, we measured the spectral regular transmittance and reflectance of materials(MgF<TEX>$_2$</TEX>, CaF<TEX>$_2$</TEX>, BaF<TEX>$_2$</TEX>, SiO<TEX>$_2$</TEX>, Sapphire) used as optical components over the spectral range between 115 nm and 230 nm.

Investigation of single-factor calibration of the wave-number scale in Fourier-transform spectroscopy

We have used the fundamental and frequency-doubled output of a single-frequency tunable laser locked to a precisely known transition in molecular iodine to provide calibration of a Fourier-transform spectrometer (FTS) in the visible and near-ultraviolet regions and to investigate the limiting uncertainty involved in calibrating spectra by using a single multiplicative correction to the entire optical frequency scale. An integrating sphere was used to introduce the laser light as a pseudoincoherent source and provide uniform illumination of the FTS field of view. The sphere also served to combine the laser beams with light from a series of mercury electrodeless discharge lamps containing argon carrier gas at selected pressures. Four strong lines in the spectrum of 198Hg were measured with these lamps to obtain precise wavelengths and argon-pressure-shift coefficients. These lines, emitted from lamps with argon pressures in the range 33 Pa (0.25 Torr) to 1330 Pa (10 Torr), are suitable for future calibration of FT spectra without need for the laser source. The limiting relative uncertainty component in the reported wavelengths is 6.19×10−9, as estimated from observed deviation of the frequency ratios of the calibration lasers from the exact value of 2. The adequacy of a single multiplicative correction factor for the absolute calibration of an individual FT spectrum is supported by our data, at the level of better than a part in 108.

Wavelength control of tunable dense wavelength-division multiplexing sources by use of a Fabry-Perot etalon and a semiconductor optoelectronic diode.

A high-resolution tunable-wavelength controller is achieved by use of an etalon for control of wavelength drift and a semiconductor optical diode (SOD) for channel recognition. The etalon provides a stable wavelength reference, and the SOD can detect mode-hopping and incomplete-tuning problems in tuning a laser. With the help of a Fabry-Perot etalon as a precise wavelength reference, the usual concern with the temperature stability of a SOD can be relaxed at least tenfold compared with wavelength control with a single SOD. We demonstrate the feasibility of monitoring tunable lasers by using a Fabry-Perot laser diode (FPLD) or a semiconductor optical amplifier (SOA). The induced voltage of the FPLD and that of the SOA are modeled with analytic expressions that can help to optimize the operation of a SOD sensor.