Scanning Fabry-Perot Interferometer Research Articles

The Brillouin linewidth in water as a function of temperature and salinity: the missing empirical relationship

Brillouin scattering in water has been proposed as a method to measure temperature profiles in the ocean. Spontaneous Brillouin scattering can be understood as light scattering on phonons in the water originating from thermal fluctuations. The scattering signal usually features three peaks in its spectrum, of which one is attributed mainly to scattering from suspended particles and shows no frequency shift from the incident light, while the other two are shifted by the phonon frequency leading to a linear dependency of this Brillouin shift to the speed of sound. The speed of sound is dependent on temperature and salinity. To measure temperature and salinity independently, a second measurement parameter is necessary. The spectral width of the Brillouin lines constitutes a measure for the phonon lifetime and depends on various macroscopic water properties. This linewidth was investigated in a laboratory using a scanning FPI (Fabry-Perot interferometer) over a temperature range from 1.8 °C to 35 °C and 13 salinities from 0 ppt to 36 ppt. A strong temperature dependence was confirmed and a weaker, nonlinear dependency on salinity was found. An empirical model was created to describe the data for the purpose of enabling remote sensing of water temperature profile and salinity simultaneously in the future.

Stellar feedback impact on the ionized gas kinematics in the dwarf galaxy Sextans B

ABSTRACT We investigated the ionized and atomic gas kinematics and excitation state in the central region of ongoing star formation of the nearby low-metallicity dwarf galaxy Sextans B. The analysis is based on the new observations performed in the H α emission line with high resolution (R ∼ 16 000) scanning Fabry–Perot interferometer at the 6-m BTA Special Astrophysical Observatory of the Russian Academy of Sciences telescope, and on the long-slit spectral observations at the 9.2-m SALT and 2.5-m Caucasian Mountain Observatory of Sternberg Astronomical Institute of Moscow State University telescopes. Strong non-circular gas motions detected in the studied regions probably resulted from the off-plane gas motions and impact of stellar feedback. We identified six regions of elevated H α velocity dispersion, five of which exhibit asymmetric or two-component H α line profiles. Three of these regions are young (<1.1 Myr) expanding ($V_\mathrm{exp} \sim 25-50 \, \mbox{km}\, \mbox{s}^{-1}$) superbubbles. We argue that at least three regions in the galaxy could be supernova remnants. We conclude that supernovae feedback is the dominant source of energy for superbubbles in Sextans B, which is expected for such a low metallicity, although we cannot rule out a strong impact of pre-supernova feedback for one superbubble.

S0 Galaxies: Outer Gas Accretion through Tidal Interaction and Minor Merging

To clarify the sources of outer gas accretion onto disk galaxies, we study the vicinity of four interacting galaxy systems in the Hα emission line by using the scanning Fabry–Perot interferometer of the 6m telescope of the Special Astrophysical Observatory RAS. We find perspective accretion flows seen as ionized-gas emission filaments between the galaxies. We discuss the whole kinematics and origin of these flows.

Gas and Stars in the Teacup Quasar Looking with the 6-m Telescope

New results on the radio-quiet type 2 quasar, known as the Teacup galaxy (SDSSJ1430+1339), based on the long-slit and 3D spectroscopic data obtained at the Russian 6-m telescope, are presented. The ionized gas giant nebula, which extends up to r=56 kpc in the [O iii] emission line, was mapped with the scanning Fabry–Perot interferometer. The direct estimation of the emission line ratios confirmed that the giant nebula is ionized by the AGN. Stars in the inner r<5 kpc are significantly younger than the outer host galaxy and have a solar metallicity. The central starburst age (∼1 Gyr) agrees with possible ages for the galactic merger events and the previous episode of the quasar outflow produced two symmetric arcs visible in the [O iii] emission at the distances r= 50–55 kpc. The ionized gas velocity field can be fitted by the model of a circular rotating disk significantly inclined or even polar to the stellar host galaxy.

Injection-locked highly Yb3+-doped uncoupled-61-core phosphate fiber laser.

Uncoupled multicore fibers are promising platforms for advanced optical communications, optical computing, and novel laser systems. In this paper, an injection-locked highly ytterbium (Yb3+)-doped uncoupled-61-core phosphate fiber laser at 1030 nm is reported. The 61-core fiber with a core-to-core pitch of 20 μm was fabricated with the stack-and-draw technique. Each core doped with 6-wt.% Yb3+ ions has a diameter of 3 μm and numerical aperture of 0.2. Linearly polarized single-frequency output of 9.1 W was obtained from the injection-locked cavity with a 10-cm-long gain fiber at a pump power of 23.6 W. The injection locking of all 61 cores was confirmed by inspecting the longitudinal modes of the individual lasers with a scanning Fabry-Perot interferometer. The performance of the injection-locked 61-core fiber laser was characterized and compared to that of the free-running operation in terms of optical spectrum, near- and far-field intensity profiles, and relative intensity noise.

Stellar feedback impact on the ionized gas kinematics in the dwarf galaxy Sextans A

ABSTRACT Feedback from massive stars shapes the interstellar medium (ISM) and affects the evolution of galaxies, but its mechanisms acting at the small scales (∼10 pc) are still not well constrained observationally, especially in the low-metallicity environments. We present the analysis of the ionized gas (focusing on its kinematics, which were never studied before) and its connection to the massive stars in the nearby (D ∼ 1.4 Mpc) star-forming very metal poor ($Z\sim 0.07 \, \mathrm{Z}_\odot$) galaxy Sextans A. The analysis is based on the observations with a scanning Fabry–Perot interferometer, long-slit spectroscopy, and imaging in emission lines with narrow-band tunable filters. We found 10 expanding superbubbles of ionized gas with ages of 1–3 Myr. We argue that three of them are probable supernova remnants, while the pre-supernova feedback is an important source of energy for blowing out the remaining superbubbles. The two brightest sites of star formation exhibit signs of outflowing ionized gas, which is traced by its ionized and atomic gas kinematics and (in one case) by its emission line flux ratios. Overall, the ionized gas kinematics in Sextans A is highly affected by the feedback from several generations of massive stars and inconsistent with the mere solid-body rotation observed in atomic hydrogen.

Tunable single-mode chip-scale mid-infrared laser

Portable mid-infrared (mid-IR) spectroscopy and sensing applications require widely tunable, chip-scale, single-mode sources without sacrificing significant output power. However, no such lasers have been demonstrated beyond 3 μm due to the challenge of building tunable, high quality-factor (Q) on-chip cavities. Here we demonstrate a tunable, single-mode mid-IR laser at 3.4 μm using a tunable high-Q silicon microring cavity and a multi-mode Interband Cascade Laser. We achieve single-frequency lasing with 0.4 mW output power via self-injection locking and a wide tuning range of 54 nm with 3 dB output power variation. We further estimate an upper-bound effective linewidth of 9.1 MHz and a side mode suppression ratio of 25 dB from the locked laser using a scanning Fabry-Perot interferometer. Our laser platform based on a tunable high-Q microresonator can be expanded to higher wavelength quantum-cascade lasers and lead to the development of compact, high-performance mid-IR sensors for spectroscopic applications.

Broadband high-spatial-resolution high-spectral-resolution flexible imaging spectrometer design study.

A broadband high-spatial-resolution high-spectral-resolution flexible imaging spectrometer (B-2HSR-FIS) is presented, which includes two microlens arrays (MLAs), multiple fiber bundles, a scanning Fabry-Perot interferometer (FPI), a reflection grating, a cylindrical lens, and an area-array detector. The first MLA is arranged in a circular arc to obtain a field angle between 8° and 60° in the horizontal plane. The second MLA is arranged in a straight line. Each fiber bundle containing seven optical fibers is coupled to a separate microlens of the first MLA, subdividing the field angle of each microlens into seven smaller field angles to improve spatial resolution. The combination of a scanning FPI and a reflection grating enables the B-2HSR-FIS to obtain both high spectral resolution and broadband spectral range in the ultraviolet to near-infrared spectral region. Compared with all existing imaging spectrometers, the B-2HSR-FIS is the first to simultaneously obtain high spatial resolution, high spectral resolution, broadband spectral range, and moderate field angle, to the best of our knowledge. The B-2HSR-FIS has great potential for vision intelligence (e.g., as an eye of a robot).

Resolving the Circumstellar Environment of the Galactic B[e] Supergiant Star MWC 137.II. Nebular Kinematics and Stellar Variability*

Abstract The Galactic B[e] supergiant MWC 137 is surrounded by a large-scale optical nebula. To shed light on the physical conditions and kinematics of the nebula, we analyze the optical forbidden emission lines [N ii] λ λ 6548,6583 and [S ii] λ λ 6716,6731 in long-slit spectra taken with ALFOSC at the Nordic Optical Telescope. The radial velocities display a complex behavior but, in general, the northern nebular features are predominantly approaching while the southern ones are mostly receding. The electron density shows strong variations across the nebula with values spreading from about zero to ∼800 cm−3. Higher densities are found closer to MWC 137 and in regions of intense emission, whereas in regions with high radial velocities the density decreases significantly. We also observe the entire nebula in the two [S ii] lines with the scanning Fabry–Perot interferometer attached to the 6 m telescope of the Special Astrophysical Observatory. These data reveal a new bow-shaped feature at P.A. = 225°–245° and a distance 80″ from MWC 137. A new Hα image has been taken with the Danish 1.54 m telescope on La Silla. No expansion or changes in the nebular morphology appear within 18.1 yr. We derive a mass of 37 − 5 + 9 M ☉ and an age of 4.7 ± 0.8 Myr for MWC 137. Furthermore, we detect a period of 1.93 d in the time series photometry collected with the TESS satellite, which could suggest stellar pulsations. Other, low-frequency variability is seen as well. Whether these signals are caused by internal gravity waves in the early-type star or by variability in the wind and circumstellar matter currently cannot be distinguished.

CW Direct Detection Lidar with a Large Dynamic Range of Wind Speed Sensing in a Remote and Spatially Confined Volume

A novel continuous-wave (CW) direct detection lidar (DDL) is demonstrated to be capable of wind speed measurement 40 m away with an update rate of 4 Hz using a fiber-based scanning Fabry–Perot interferometer as an optical frequency discriminator. The proposed CW DDL has a large dynamic wind speed range with no sign ambiguity and its sensitivity is assessed by comparing its performance with that of a CW coherent detection lidar (CDL) in a side-by-side wind measurement. A theoretical model of the spatial weighting function of the fiber-based CW DDL is also presented and validated experimentally. This work shows that the CW DDL has a spatially confined measurement volume with a Lorentzian axial profile similar to that of a CW CDL. The proposed DDL has potential use in various applications in which requirements such as high-speed wind sensing and directional discrimination are not met by state-of-the-art Doppler wind lidar systems.

Proper motions of spectrally selected structures in the HH 83 outflow

Context. We continue our program of investigation of the proper motions of spectrally separated structures in the Herbig–Haro outflows with the aid of Fabry–Perot scanning interferometry. This work mainly focuses on the physical nature of various structures in the jets. Aims. The aim of the present study is to measure the proper motions of the previously discovered kinematically separated structures in the working surface of the HH 83 collimated outflow. Methods. We used observations from two epochs separated by 15 yr, which were performed on the 6 m telescope with Fabry–Perot scanning interferometer. We obtained images corresponding to different radial velocities for the two separate epochs, and used them to measure proper motions. Results. In the course of our data analysis, we discovered a counter bow-shock of HH 83 flow with positive radial velocity, which makes this flow a relatively symmetric bipolar system. The second epoch observations confirm that the working surface of the flow is split into two structures with an exceptionally large (250 km s−1) difference in radial velocity. The proper motions of these structures are almost equal, which suggests that they are physically connected. The asymmetry of the bow shock and the turning of proper motion vectors suggests a collision between the outflow and a dense cloud. The profile of the Hα line for the directly invisible infrared source HH 83 IRS, obtained by integration of the data within the reflection nebula, suggests it to be of P Cyg type with a broad absorption component characteristic of the FU Ori-like objects. If this object underwent an FU Ori type outburst, which created the HH 83 working surfaces, its eruption took place about 1500 years ago according to the kinematical age of the outflow.

Scanning Fabry–Perot Interferometer of the 6-m SAO RAS Telescope

The scanning Fabry-Perot interferometer (FPI) - is the oldest method of optical 3D spectroscopy. It is still in use because of the high spectral resolution it provides over a large field of view. The history of the application of this method for the study of extended ob jects (nebulae and galaxies) and the technique of data reduction and analysis are discussed. The paper focuses on the performing observations with the scanning FPI on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS). The instrument is currently used as a part of the SCORPIO-2 multimode focal reducer. The results of studies of various galactic and extragalactic objects with the scanning FPI on the 6-m telescope - star-forming regions and young stellar objects, spiral, ring, dwarf and interacting galaxies, ionization cones of active galactic nuclei, galactic winds, etc. are briefly discussed. Further prospects for research with the scanning FPI of the SAO RAS are discussed.

Search for gas accretion imprints in voids: II. The galaxy Ark 18 as a result of a dwarf–dwarf merger

ABSTRACT The low-mass low-surface brightness (LSB) disc galaxy Arakelian 18 (Ark 18) resides in the Eridanus void and because of its isolation represents an ideal case to study the formation and evolution mechanisms of such a galaxy type. Its complex structure consists of an extended blue LSB disc and a bright central elliptically shaped part hosting a massive off-centred star-forming clump. We present the in-depth study of Ark 18 based on observations with the SCORPIO-2 long-slit spectrograph and a scanning Fabry–Perot interferometer at the Russian 6-m telescope complemented by archival multiwavelength images and SDSS spectra. Ark 18 appears to be a dark matter dominated gas-rich galaxy without a radial metallicity gradient. The observed velocity field of the ionized gas is well described by two circularly rotating components moderately inclined with respect to each other and a possible warp in the outer disc. We estimated the age of young stellar population in the galaxy centre to be ∼140 Myr, while the brightest star-forming clump appears to be much younger. We conclude that the LSB disc is likely the result of a dwarf–dwarf merger with a stellar mass ratio of the components at least ∼5:1 that occurred earlier than 300 Myr ago. The brightest star-forming clump was likely formed later by accretion of a gas cloud.

Phase retrieval of nanosecond laser pulses based on temporal shearing interferomentry

Temporal shearing interferometry is proposed to measure the temporal phase distribution of nanosecond laser pulses. In the proposed scheme, the pulse to be measured is divided into two pulses with a delay of hundreds of picoseconds in between, arbitrary one of the two pulses is added to by an appropriate amount of frequency shift, then is combined with the remaining pulse, thereby obtaining the temporal shearing interferogram that is recorded by a normal photodiode. The temporal phase distribution is calculated by an adaptive algorithm based on Fourier transform, and further the precise spectra of the measured pulse can also be calculated according to the Fourier relation between time domain and spectral domain. Based on the systematic analysis of the principle of the technology, the proposed technology is verified by numerical simulation. And the influence of the variable parameters including noise, relative delay, relative intensity on the measured error are systematically analyzed in the simulation. And the results show that the proposed nanosecond temporal phase diagnostic technique has a good performance when the signal noise ratio of the interferogram is above 15 dB, the relative delay of the pulses is between 0.5% and 28% and the relative intensity is above 0.1%. The proposed method is verified experimentally in a nanosecond laser system with central wavelength of 640 nm and pulse width of 20 ns. And the calculated spectra obtained from the temporal shearing interferogram match well with the spectra measured by a scanning Fabry-Perot interferometer. This proposed technique does not use any nonlinear optical effects, thus it can be applied to the diagnostic of nanosecond laser pulse centered at any wavelength. Hence, it provides a simple experimental setup for implementing the higher-accuracy diagnostic of the temporal phase distribution of nanosecond laser pulses.

High-power narrow-linewidth single-frequency pulsed fiber amplifier based on self-phase modulation suppression via sawtooth-shaped pulses

Fiber laser system in master oscillator power amplifier (MOPA) scheme is a promising technique for high-power narrow-linewidth laser output. With modulation-generated pulsed seed laser, the fiber MOPA benefits the flexible temporal behavior. However, the spectral linewidth broadening induced by self-phase modulation (SPM) is the main obstacle to achieving high-power single-frequency laser output with narrow spectral linewidth, especially for pulsed fiber MOPA in which the kilowatts level peak power results in strong nonlinearity. The SPM induced linewidth broadening is related to the derivative of light intensity with respect to time (d<i>I</i>/d<i>t</i>). Theoretically, if the d<i>I</i>/d<i>t</i> of the laser pulse is a constant, the SPM process will not generate any new frequency components. Hence, the linewidth broadening can be suppressed. In this work, we demonstrate a high-power single-frequency Yb fiber amplifier at 1064 nm, in which a sawtooth laser pulse is employed to suppress the SPM induced linewidth broadening, for obtaining the output with near-transform-limited narrow linewidth. The sawtooth-shaped seed pulse train is generated through using an electro-optic intensity modulator to modulate the continuous-wave (CW) output of a single-frequency fiber laser. After being pre-amplified, the seed laser with a pulse repetition rate of 20 kHz is coupled into the main amplifier, in which a piece of 0.9-m-long Yb-doped silica fiber with core and clad diameters of 35 μm and 250 μm, respectively, is used as a gain medium. The seed laser is enhanced to an average power value of 3.13 W under a launched 976-nm pump power value of 11.3 W before the onset of stimulate Brillouin scattering. The pulse energy 157 μJ and the pulse width 6.5 ns give a peak power of 24 kW. The spectral linewidth measured using a scanning Fabry-Perot interferometer at the maximum power is only 83 MHz, which is quite close to the 76-MHz transform-limited linewidth of the 6.5-ns sawtooth-shaped pulse. For comparison, we also conduct an experiment with a common Gaussian-shaped seed laser, in which the spectral linewidth is broadened significantly with a peak power value of only 1.5 kW. The results here reveal that the using of the sawtooth-shaped pulse is a promising technique to suppress the SPM induced spectral linewidth broadening in high-peak-power fiber amplifiers and acquire near-transform-limited narrow-linewidth laser output.

Ionized Gas in the NGC 3077 Galaxy

The nearby dwarf galaxy NGC 3077 is known for its peculiar morphology, which includes numerous dust lanes and emission-line regions. The interstellar medium in this galaxy is subject to several perturbing factors. These are primarily the central starburst and tidal structures in the M 81 group. We present a comprehensive study of the state of ionization, kinematics, and chemical composition of ionized gas in NGC 3077, including both star-forming regions and diffuse ionized gas (DIG) at the periphery. We study gas motions in the H$\alpha$ line via high-resolution ($R\approx15\,000$) 3D spectroscopy with the scanning Fabry-Perot interferometer installed into SCORPIO-2 instrument attached to the 6-m telescope of the SAO RAS. Images in the main optical emission lines were acquired with MaNGaL photometer with a tunable filter at the 2.5-m telescope of the Caucasian Mountain Observatory of SAI MSU. We also used SCORPIO-2 to perform long-slit spectroscopy of the galaxy with a resolution of $R\approx1\,000$. Our estimate of the gas metallicity, $Z=0.6Z_\odot$, is significantly lower than the earlier determination, but agrees with the "luminosity--metallicity" dependence. Spatially resolved diagnostic diagrams of the emission-line ratios do not show correlations between the gas ionization state and its velocity dispersion, and this is most likely due to strong ionization by young stars, whereas the contribution of shocks to the excitation of emission lines is less important. We also studied the locations of multicomponent H$\alpha$ profiles and provide arguments suggesting that they are mostly associated with individual kinematic components along the line of sight and not with expanding shells as it was believed earlier. We also observe there a combination of wind outflow from star-forming regions and accretion from interstellar gas clouds in the M 81 group.

Mapper of Narrow Galaxy Lines (MaNGaL): new tunable filter imager for Caucasian telescopes

We described the design and operation principles of a new tunable-filter photometer developed for the 1-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences and the 2.5-m telescope of the Sternberg Astronomical Institute of the Moscow State University. The instrument is mounted on the scanning Fabry-Perot interferometer operating in the tunable-filter mode in the spectral range of 460-800 nm with a typical spectral resolution of about 1.3 nm. It allows one to create images of galactic and extragalactic nebulae in the emission lines having different excitation conditions and to carry out diagnostics of the gas ionization state. The main steps of observations, data calibration, and reduction are illustrated by examples of different emission-line objects: galactic HII regions, planetary nebulae, active galaxies with extended filaments, starburst galaxies, and Perseus galaxy cluster.

Theoretical analysis of compact ultrahigh-spectral-resolution infrared imaging spectrometer.

A compact ultrahigh-spectral-resolution imaging spectrometer (CUSRIS) is presented, which combines an entrance slit, a scanning Fabry-Perot interferometer (FPI), a static grating interferometer (SGI) and a cylindrical lens. The SGI consists of a beam splitter, a fixed reflection grating in Littrow configuration, and a fixed plane mirror. For each point of the entrance slit, one spectral image is obtained at each FPI spacing position, and multiple spectral images are obtained to synthesize an ultrahigh-spectral-resolution spectral image. First-order approximations of system performance are given. The CUSRIS is a unique concept that not only obtains spatial information and ultrahigh-resolution spectral information (e.g., resolving power higher than 1,000,000) in the near-infrared, short-wave infrared or mid-wave infrared region, but also has the advantages of compact size and short measurement time compared with the existing ultrahigh-spectral-resolution infrared imaging spectrometers.

On the performance of wavelength meters: Part 1—consequences for medium-to-high-resolution laser spectroscopy

Present-day laser-spectroscopy experiments increasingly rely on modern commercial devices to monitor, stabilize, and scan the wavelength of their probe laser. Recently, new techniques are capable of achieving unprecedented levels of precision on atomic and nuclear observables, pushing these devices to their performance limits. Considering the fact that these observables themselves are deduced from the frequency difference between specific atomic resonances, in the order of MHz–GHz, the uncertainty on the output of the device measuring the wavelength is often directly related to the final systematic uncertainty on the experimental results. Owing to its importance, the performance of several commercial wavelength meters was compared against different reference sources, including a Scanning Fabry–Perot Interferometer (SFPI) and a frequency comb. Reproducible, wavelength- and device-dependent disagreements are observed, potentially skewing the experimental output at high precision. In this paper, a practical and relatively inexpensive wavelength meter characterization procedure is presented and validated. This method is capable of improving the precision on wavelength differences considerably depending on the device, while together with a second investigation that is published separately, (Konig et al., in Appl Phys B, 2020), it offers a full description of the expected wavelength meter performance for users.

Single-frequency DBR Nd-doped fiber laser at 1120 nm with a narrow linewidth and low threshold.

We report a narrow linewidth and low threshold single-frequency distributed Bragg reflector (DBR) fiber laser at 1120 nm based on a short 1.5 cm long Nd-doped silica fiber which, to the best of our knowledge, is the first demonstration of a Nd-doped fiber-based single-frequency fiber laser with a wavelength greater than 1100 nm. A stable single-longitudinal-mode laser operation with a signal-to-noise ratio greater than 67 dB was verified by a scanning Fabry-Perot interferometer. The laser threshold is as low as 10 mW. The DBR fiber laser has a maximum output power of 15 mW and optical-to-optical efficiency for the launched pump power reaches more than 8%. The narrow linewidth of 71.5 kHz is obtained in such a single-frequency fiber laser (SFFL). Our result is expected to offer an exciting new opportunity to realize high-performance SFFLs above 1100 nm.