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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Optics and Lasers".

Deadline for manuscript submissions: closed (30 September 2020) | Viewed by 37947

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Dr. Daniel Sola

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Guest Editor

Marie Skłodowska-Curie Individual Fellow, Professur für Laserbasierte Methoden der großflächigen Oberflächenstrukturierung, Institut für Fertigungstechnik, Technische Universität Dresden, Dresden, 01062 Dresden, Germany
Interests: laser spectroscopy; laser–matter interaction; ultrashort lasers; laser processing; ophthalmic polymers; ocular tissues; photonic devices
Special Issues, Collections and Topics in MDPI journals

Dr. Eugenio Cantelar

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Associate Professor, Departamento de Física de Materiales, Universidad Autónoma de Madrid, 28049 Madrid, Spain
Interests: laser spectroscopy; spectroscopic characterization; rare-earth doped materials; nanoparticles; active waveguides; optical amplification; lasers

Special Issue Information

Dear Colleagues,

Since their invention in 1960, lasers have been successfully applied to both fundamental and applied research. In particular, laser spectroscopy is a powerful technique which has been used in physics, chemistry, and biology to study and unravel the structure of matter by using laser light as a pumping probe. The development of solid-state and tunable lasers working in both continuous and pulsed mode has resulted in a sensitive, versatile tool for sensing and analytical applications.

This Special Issue covers the whole spectrum of laser spectroscopy, ranging from the study of the interaction of radiation with matter in terms of absorption, fluorescence, and scattering to UV–vis–IR spectroscopy, imaging, ultrafast laser spectroscopy, optical sources, and remote sensing. The topics of this Special Issue include fundamental, applied, technological, and industrial aspects of laser spectroscopy. Novel applications in optics, photonics, energy, and biomedicine, as well in materials science and technology, are warmly welcome.

It is our pleasure to invite you to submit a manuscript to this Special Issue. Full papers, short communications, and reviews would be greatly appreciated.

Dr. Daniel Sola
Dr. Eugenio Cantelar
Guest Editors

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Keywords

interaction between laser radiation and matter
absorption
fluorescence
scattering
UV–vis–IR spectroscopy
laser-based sensing in solids
imaging
laser sources
simulation analysis

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Published Papers (10 papers)

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10 pages, 9104 KiB

Open AccessArticle

Spectroscopy and Near-Infrared to Visible Upconversion of Er³⁺ Ions in Aluminosilicate Glasses Manufactured with Controlled Optical Transmission

by Daniel Sola, Adrián Miguel, Eduardo Arias-Egido and Jose I. Peña

Appl. Sci. 2021, 11(3), 1137; https://doi.org/10.3390/app11031137 - 26 Jan 2021

Cited by 7 | Viewed by 2096

Abstract

In this work we report on the spectroscopic properties and the near-infrared to visible upconversion of Er³⁺ ions in aluminosilicate glasses manufactured by directionally solidification with the laser floating zone technique. Glasses were manufactured in a controlled oxidizing atmosphere to provide them with high optical transmission in the visible spectral range. Absorption and emission spectra, and lifetimes were assessed in both the visible and the near infrared spectral range. Green upconversion emissions of the ²H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 transitions at 525 nm and 550 nm attributed to a two-photon process were observed under excitation at 800 nm. Mechanisms responsible for the upconversion luminescence were discussed in terms of excited state absorption and energy transfer upconversion processes. Excitation spectra of the upconverted emission suggest that energy transfer upconversion processes are responsible for the green upconversion luminescence. Full article

(This article belongs to the Special Issue Laser Spectroscopy)

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11 pages, 7530 KiB

Open AccessArticle

Temperature Sensing with Nd³⁺ Doped YAS Laser Microresonators

by Daniel Walo-Martín, Franzette Paz-Buclatin, Susana Ríos, Inocencio R. Martín, Leopoldo L. Martin, Airán Ródenas, Vladimir N. Sigaev, Vitaliy I. Savinkov and Georgiy Y. Shakhgildyan

Appl. Sci. 2021, 11(3), 1117; https://doi.org/10.3390/app11031117 - 26 Jan 2021

Cited by 5 | Viewed by 2829

Abstract

Yttria–alumina–silica (YAS) glass microspheres doped with Nd³⁺ ions were excited with a 532 nm continuous laser in order to study the dependency of the wavelength of the whispering gallery mode (WGM) peaks on the temperature of the sample. This was possible due to a previous calibration of the 808 nm and 890 nm emission bands of the Nd:YAS glass sample for different temperatures using the fluorescence intensity ratio (FIR) technique. A maximum sensitivity of 15 × 10⁻⁶ K⁻¹ and a temperature resolution limit of 0.2 K were obtained for the microsphere sensor. Moreover, laser emission at 1064 nm was observed by continuous pumping at 532 nm, and a power threshold of 100 mW was determined. Upconversion emissions of Nd³⁺ were also studied by exciting the sample at 808 nm. Full article

(This article belongs to the Special Issue Laser Spectroscopy)

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19 pages, 3739 KiB

Open AccessFeature PaperArticle

Multianalyzer Spectroscopic Data Fusion for Soil Characterization

by Richard R. Hark, Chandra S. Throckmorton, Russell S. Harmon, John R. Plumer, Karen A. Harmon, J. Bruce Harrison, Jan M. H. Hendrickx and Jay L. Clausen

Appl. Sci. 2020, 10(23), 8723; https://doi.org/10.3390/app10238723 - 5 Dec 2020

Cited by 14 | Viewed by 2682

Abstract

The ability to rapidly conduct in-situ chemical analysis of multiple samples of soil and other geological materials in the field offers many advantages over a traditional approach that involves collecting samples for subsequent examination in the laboratory. This study explores the application of complementary spectroscopic analyzers and a data fusion methodology for the classification/discrimination of >100 soil samples from sites across the United States. Commercially available, handheld analyzers for X-ray fluorescence spectroscopy (XRFS), Raman spectroscopy (RS), and laser-induced breakdown spectroscopy (LIBS) were used to collect data both in the laboratory and in the field. Following a common data pre-processing protocol, principal component analysis (PCA) and partial least squares discriminant analysis (PLSDA) were used to build classification models. The features generated by PLSDA were then used in a hierarchical classification approach to assess the relative advantage of information fusion, which increased classification accuracy over any of the individual sensors from 80-91% to 94% and 64-93% to 98% for the two largest sample suites. The results show that additional testing with data sets for which classification with individual analyzers is modest might provide greater insight into the limits of data fusion for improving classification accuracy. Full article

(This article belongs to the Special Issue Laser Spectroscopy)

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13 pages, 4385 KiB

Open AccessArticle

Evolution of Whispering Gallery Modes in Li-Doped ZnO Hexagonal Micro- and Nanostructures

by Rocío Ariza, Belén Sotillo, Fernando Pavón, Ana Urbieta and Paloma Fernández

Appl. Sci. 2020, 10(23), 8602; https://doi.org/10.3390/app10238602 - 1 Dec 2020

Cited by 6 | Viewed by 2631

Abstract

The formation of optical cavities in Li-doped ZnO nanostructures was investigated. By means of the vapor–solid method, long micro- and nanostructures with a hexagonal cross-section were grown. These morphologies were favorable for Fabry-Pérot and whispering gallery modes to appear. A variety of structures with different sections was studied using µ-photoluminescence in both the transverse electric (TE) and transverse magnetic (TM) polarizations, showing well-pronounced optical resonant modes. The results showed a dominance of whispering gallery modes that were in good agreement with the calculated refractive index. The quality factor (Q) and finesse (F) were estimated, which demonstrated the quality of Li:ZnO structures as optical cavities. Full article

(This article belongs to the Special Issue Laser Spectroscopy)

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12 pages, 2517 KiB

Open AccessArticle

An Automatic Optimized Method for a Digital Optical Phase Conjugation System in Focusing through Scattering Media

by Pan Zhang, Zhan Li, Lu Han, Dean Liu and Jianqiang Zhu

Appl. Sci. 2020, 10(23), 8321; https://doi.org/10.3390/app10238321 - 24 Nov 2020

Cited by 2 | Viewed by 2192

Abstract

In this paper, a reliable automatic optimized method for a digital optical phase conjugation (DOPC) system based on a multipopulation genetic algorithm (MPGA) is proposed for improving the compensation quality of DOPC. The practical implementation and compensation quality of DOPC in focusing through scattering media are greatly limited by imperfect pixel alignment, optical aberration, and mechanical error in the DOPC system. For comprehensively solving the above problems, the concept of global optimization is introduced by Zernike polynomials (Zernike modes) to characterize overall imperfections, and MPGA is used to search for the most optimal Zernike coefficient and compensate for the overall imperfections of the DOPC system. The significant optimization ability of the proposed method is verified in DOPC-related experiments for focusing through scattering media. The peak-to-background ratio (PBR) of the OPC focus increases 174 times that of the initial OPC focus. Furthermore, we evaluated the optimization results of the proposed method with a fitness function of intensity fitness and correlation coefficient fitness in MPGA. The results show that the optimized capability is excellent and more efficiently used than the correlation coefficient fitness function in the Zernike modes. Full article

(This article belongs to the Special Issue Laser Spectroscopy)

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13 pages, 17699 KiB

Open AccessArticle

Measuring the Hyperfine Splitting and Deriving the Hyperfine Interaction Constants of the Cesium 5p⁶7d ²D_5/2 Excited State

by Zerong Wang, Xiaokai Hou, Jiandong Bai and Junmin Wang

Appl. Sci. 2020, 10(22), 8178; https://doi.org/10.3390/app10228178 - 18 Nov 2020

Cited by 3 | Viewed by 4118

Abstract

The measurement of the cesium (Cs) 5p⁶7d²D_5/2 excited state’s hyperfine splitting intervals and hyperfine interaction constants was experimentally investigated using a ladder-type (852 nm + 698 nm) three-level Cs system (5p⁶6s²S_1/2–5p⁶6p²P_3/2–5p⁶7d²D_5/2) with a room-temperature Cs atomic vapor cell. By scanning the 698 nm coupling laser’s frequency, the Doppler-free high-resolution electromagnetically-induced transparency (EIT)-assisted double-resonance optical pumping (DROP) spectra were demonstrated via transmission enhancement of the locked 852 nm probe laser. The EIT-assisted DROP spectra were employed to study the hyperfine splitting intervals for the Cs 5p⁶7d²D_5/2 excited state with a room-temperature Cs atomic vapor cell, and the radio-frequency modulation sideband of a waveguide-type electro-optic phase modulator (EOPM) was introduced for frequency calibration to improve the accuracy of frequency interval measurement. The existence of EIT makes the DROP spectral linewidth much narrower, and it is very helpful to significantly improve the spectroscopic resolution. Benefiting from the higher signal-to-noise ratio (SNR) and much better resolution of the EIT-assisted DROP spectra, the hyperfine splitting intervals between the hyperfine folds of (F” = 6), (F” = 5), and (F” = 4) of the Cs 5p⁶7d²D_5/2 state (HFS_6″–5″ = −10.60(17) MHz and HFS_5″–4″ = −8.54(15) MHz) were measured and, therefore, the magnetic dipole hyperfine interaction constant (A = −1.70(03) MHz) and the electrical quadrupole hyperfine interaction constant (B = −0.77(58) MHz) were derived for the Cs 5p⁶7d²D_5/2 state. These constants constitute an important reference value for an improvement of the precise measurement and determination of basic physical constants. Full article

(This article belongs to the Special Issue Laser Spectroscopy)

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12 pages, 2942 KiB

Open AccessArticle

Raman Laser Spectrometer: Application to ¹²C/¹³C Isotope Identification in CH₄ and CO₂ Greenhouse Gases

by Vladimir Vitkin, Anton Polishchuk, Ian Chubchenko, Evgeniy Popov, Konstantin Grigorenko, Artem Kharitonov, Arsen Davtian, Anton Kovalev, Valeria Kurikova, Patrice Camy, Pavel Loiko, Magdalena Aguiló, Francesc Díaz and Xavier Mateos

Appl. Sci. 2020, 10(21), 7473; https://doi.org/10.3390/app10217473 - 24 Oct 2020

Cited by 25 | Viewed by 4260

Abstract

A compact Raman laser gas spectrometer is developed. It comprises a high-power green laser at 532.123 nm as an excitation source and a specially designed gas cell with an internal volume of less than 0.6 cm³ that can withstand gas pressures up to 100 atm. The resolution of the spectrometer is ~1 cm⁻¹. The Raman spectra of chemically pure isotopically enriched carbon dioxide (¹²CO₂, ¹³CO₂) and methane (¹²CH₄, ¹³CH₄) gases are studied. The expected limit of detection (LOD) is less than 100 ppm for the isotopologues of CO₂ and less than 25 ppm for those of CH₄ (at a gas pressure of 50 atm.), making the developed spectrometer promising for studying the sources of emissions of greenhouse gases by resolving their isotopologue composition. We also show the suitability of the spectrometer for Raman spectroscopy of human exhalation. Full article

(This article belongs to the Special Issue Laser Spectroscopy)

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20 pages, 2396 KiB

Open AccessArticle

Band-Limited Reference-Free Speckle Spectroscopy: Probing the Fluorescent Media in the Vicinity of the Noise-Defined Threshold

by Dmitry Zimnyakov, Elena Isaeva, Anna Isaeva and Sergey Volchkov

Appl. Sci. 2020, 10(5), 1629; https://doi.org/10.3390/app10051629 - 29 Feb 2020

Cited by 1 | Viewed by 2202

Abstract

A method of reference-free speckle spectroscopy based on the statistical analysis of intensity spatial fluctuations of the spectrally-selected multiple-scattered fluorescence radiation is examined in the case of the finite-band spectral selection of fluorescence light emitted by the laser-pumped random medium, and detection conditions far from the ideal case. Intensity fluctuations are recorded during point-to-point scanning of the surface of a random multiple-scattering medium, which is characterized by the dependences of the second- and third-order statistical moments of intensity on the wavelength of detected spectrally selected light. In turn, the statistical moments of intensity fluctuations are determined by the average propagation path of fluorescent radiation in the medium. This makes it possible to analyze the features of the light-medium interactions at a scale of the order of the transport mean free path of radiation propagation in the medium. Depending on the spectral selection conditions, the method is applicable for characterizing micro- or nano-structured fluorescent layers with thicknesses from tens of micrometers to several millimeters. In the examined case, the finite-band spectral selection results in the values of coherence length of the detected fluorescence radiation compared with the ensemble-averaged absolute value of the path-length difference between the stochastically interfering and spectrally selected partial contributions to the fluorescence field. In addition, non-ideal detection conditions (usage of a multimode optical fiber in the light-collecting unit) cause additional strong damping of the detected speckle intensity fluctuations. These factors lead to a remarkable suppression of spatial fluctuations of the fluorescence intensity in the course of spatially- and spectrally-resolved surface scanning of the laser-pumped probed random medium. Nevertheless, with appropriate procedures of the intrinsic noise reduction and data correction, the obtained spectral dependencies of the normalized third-order statistical moment of the band-limited fluorescence intensity clearly indicate the fluorescence propagation features in the probed multiple-scattering random media (such as a strong influence of the scattering strength and multiple self-absorption–re-emission events on the average propagation path of light in the medium).The possibilities of noise reduction and data correction in the case of applying the band-limited reference-free spectroscopic instrumentation with low spectral and spatial resolution are illustrated by the experimental results obtained using the Rhodamine-6G-doped and continuous wave (CW)-laser-pumped layers of the densely packed titania and silica particles. Full article

(This article belongs to the Special Issue Laser Spectroscopy)

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8 pages, 4642 KiB

Open AccessArticle

Precise Measurement of Hyperfine Structure of Cesium 7S_1/2 Excited State

by Yunhui He, Jiabei Fan, Liping Hao, Yuechun Jiao and Jianming Zhao

Appl. Sci. 2020, 10(2), 525; https://doi.org/10.3390/app10020525 - 10 Jan 2020

Cited by 3 | Viewed by 7400

Abstract

We present a precise measurement of the hyperfine structure of cesium

7 S_{1 / 2}

excited state by employing electromagnetically induced spectroscopy (EIS) with a cesium three-level cascade ( [...] Read more.

We present a precise measurement of the hyperfine structure of cesium

7 S_{1 / 2}

excited state by employing electromagnetically induced spectroscopy (EIS) with a cesium three-level cascade (

6 S_{1 / 2} - 6 P_{3 / 2} - 7 S_{1 / 2}

) atom in a room temperature vapor cell. A probe laser,

λ_{p}

= 852 nm, was coupled to a transition

| 6 S_{1 / 2} ⟩ \to | 6 P_{3 / 2} ⟩

, related frequency locked to the resonance hyperfine transition of

| 6 S_{1 / 2} ⟩ \to | 6 P_{3 / 2} ⟩

with a Fabry–Perot (FP) cavity and an electro-optic modulator (EOM). A coupling laser,

λ_{c}

= 1470 nm, drove the

| 6 P_{3 / 2} ⟩ \to | 7 S_{1 / 2} ⟩

transition with the frequency scanned over the

| 6 P_{3 / 2} ⟩ \to | 7 S_{1 / 2} ⟩

transition line. The hyperfine level interval was extracted to be 2183.61 ± 0.50 MHz by analyzing EIS spectroscopy. The optical–optical double-resonance (OODR) spectroscopy is also presented for comparison, with the corresponding value of the hyperfine level interval being 2183.48 MHz ± 0.04 MHz, and the measured hyperfine splitting of excited 7

S_{1 / 2}

state is shown to be in excellent agreement with the previous work. Full article

(This article belongs to the Special Issue Laser Spectroscopy)

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Review

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15 pages, 2070 KiB

Open AccessReview

Far Off-Resonance Laser Frequency Stabilization Technology

by Chang Liu, Ziqian Yue, Zitong Xu, Ming Ding and Yueyang Zhai

Appl. Sci. 2020, 10(9), 3255; https://doi.org/10.3390/app10093255 - 7 May 2020

Cited by 3 | Viewed by 5694

Abstract

In atomic physics experiments, a frequency-stabilized or ‘locked’ laser source is commonly required. Many established techniques are available for locking close to an atomic resonance. However, in many instances, such as atomic magnetometer and magic wavelength optical lattices in ultra-cold atoms, it is desirable to lock the frequency of the laser far away from the resonance. This review presents several far off-resonance laser frequency stabilization methods, by which the frequency of the probe beam can be locked on the detuning as far as several tens of gigahertz (GHz) away from atomic resonance line, and discusses existing challenges and possible future directions in this field. Full article

(This article belongs to the Special Issue Laser Spectroscopy)

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