Accurate Wavelength Calibration of an Etalon-Tuned Dye Laser

Development of a demountable and see-through hollow cathode (HC) discharge lamp suitable for optogalvanic (OG) spectroscopy is described. The design of the HC lamp is simple, compact, and inexpensive. Lithium, investigated rarely by the OG method, is selected for cathode material as its isotopes are important for nuclear industry. The HC lamp is characterized electrically and optically for discharge oscillations free OG effect. Strong OG signals of lithium as well as neon (as buffer gas) are produced precisely upon copper vapor laser pumped tunable dye laser irradiation. The HC lamp is capable of generating a clean OG resonance spectrum in the available dye laser wavelength scanning range (627.5-676 nm) obtained with 4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran dye. About 28 resonant OG lines are explicitly observed. Majority of them have been identified using j-l coupling scheme and assigned to the well-known neon transitions. One line that corresponds to wavelength near about 670.80 nm is assigned to lithium and resolved for its fine (2S1/2 → 2P1/2, 3/2) transitions. These OG transitions allow 0.33 cm-1 accuracy and can be used to supplement the OG transition data available from other sources to calibrate the wavelength of a scanning dye laser with precision at atomic levels.

Long-term wavelength drift compensation of tunable pulsed dye laser for sodium detection lidar

Abstract. Differential absorption lidar (DIAL) remote sensing is a promising technology for atmospheric CO2 detection. However, stringent wavelength accuracy and stability are required in DIAL system. Accurate on-line wavelength calibration is a crucial procedure for retrieving atmospheric CO2 concentration using the DIAL, particularly when pulsed lasers are adopted in the system. Large fluctuations in the intensities of a pulsed laser pose a great challenge for accurate on-line wavelength calibration. In this paper, a wavelength calibration strategy based on multi-wavelength scanning (MWS) was proposed for accurate on-line wavelength calibration of a pulsed laser for CO2 detection. The MWS conducted segmented sampling across the CO2 absorption line with appropriate number of points and range of widths by using a tunable laser. Complete absorption line of CO2 can be obtained through a curve fitting. Then, the on-line wavelength can be easily found at the peak of the absorption line. Furthermore, another algorithm called the energy matching was introduced in the MWS to eliminate the backlash error of tunable lasers during the process of on-line wavelength calibration. Finally, a series of tests was conducted to elevate the calibration precision of MWS. Analysis of tests demonstrated that the MWS proposed in this paper could calibrate the on-line wavelength of pulsed laser accurately and steadily.

Differential absorption lidar (DIAL) remote sensing is a promising technology for atmospheric CO<sub>2</sub> detection. However, stringent wavelength accuracy and stability are required in DIAL system. Accurate on-line wavelength calibration is a crucial procedure for retrieving atmospheric CO<sub>2</sub> concentration using the DIAL, particularly when pulsed lasers are adopted in the system. Large fluctuations in the intensities of a pulsed laser pose a great challenge for accurate on-line wavelength calibration. In this paper, a wavelength calibration strategy based on multi-wavelength scanning (MWS) was proposed for accurate on-line wavelength calibration of a pulsed laser for CO<sub>2</sub> detection. The MWS conducted segmented sampling across the CO<sub>2</sub> absorption line with appropriate number of points and range of widths by using a tunable laser. Complete absorption line of CO<sub>2</sub> can be obtained through a curve fitting. Then, the on-line wavelength can be easily found at the peak of the absorption line. Furthermore, another algorithm called the energy matching was introduced in the MWS to eliminate the backlash error of tunable lasers during the process of on-line wavelength calibration. Finally, a series of tests was conducted to elevate the calibration precision of MWS. Analysis of tests demonstrated that the MWS proposed in this paper could calibrate the on-line wavelength of pulsed laser accurately and steadily.

December 28, 1987:[...]

Studies of the optogalvanic effect in a commercial caesium hollow cathode lamp and its use for tuning pulsed dye lasers

In an attempt to understand the implications of using glow discharge atomizers in atomic absorption spectrometry (AAS), line profiles and kinetic (Doppler) temperatures were measured in commercial hollow cathode lamps and a laboratory-constructed, jet-assisted dc glow discharge atomizer using a high-resolution Bomem Fourier transform spectrometer. Line profiles were measured in the hollow cathode lamps as current was increased from 1 to 30 mA for three resonance atomic lines (Mg 285.21 nm, Al 308.22 nm, and Pb 283.31 nm) having distinctly different hyperfine structure. Although the Al 308.22-nm line was largely unaffected by self-absorption as the lamp current was increased, the Pb 283.31-nm and Mg 285.21-nm lines exhibited pronounced self-absorption broadening at relatively low lamp currents. Kinetic temperatures in the hollow cathode lamps ranged from 320 ± 20 K at low lamp currents to 840 ± 20 K at high currents. With the use of the Ar(I) 415.86-nm line from the argon discharge gas as a thermometric species, kinetic temperatures of 460 ± 20 K to 620 ± 20 K were measured in the glow discharge atomizer under typical analytical operating conditions. These low atomizer gas temperatures imply that the sensitivity and linear dynamic range of analytical calibration curves will be more strongly affected by the lamp current of the primary radiation source and the spectral properties of the analysis line in glow discharge AAS than in flame or furnace AAS, and that operation at low lamp current is essential for optimal analytical performance. The degrees to which the linear dynamic range and the slope of the analytical calibration curve would be affected by the hyperfine structure of the analysis line, the extent of self-absorption in the hollow cathode lamp, the hollow cathode kinetic temperature, and the glow discharge kinetic temperature are considered separately for each atomic line investigated. The kinetic temperatures in the hollow cathode lamps and the glow discharge atomizer were so close that it was possible to obtain absorption line profiles for the three resonance atomic lines in the glow discharge atomizer with the use of hollow cathode lamps as primary radiation sources, i.e., without the necessity of using a continuum source of radiation.

Vocal fold scar is a challenging clinical problem, resulting in a spectrum of voice-related complaints. While there are a variety of treatment options available, it is rare to obtain outcomes similar to the perfectly normal voice. The pulsed dye and other lasers are an emerging treatment option for cutaneous scar and have shown promise for the treatment of vocal fold scarring. The purpose of this review is to summarize the theory, and describe clinical outcomes from both cutaneous and vocal fold scarring treated with lasers. There are a growing number of papers in the literature substantiating the use of pulsed dye and other lasers used to treat cutaneous scars. Some experimental models describe potential mechanisms of laser effect, which include the development of a sub-basement membrane cleavage plane, as well as up-regulation of proteins which may actively modulate continued fibrosis. One prospective pilot study of 11 patients with vocal fold scarring treated with the pulsed dye laser has also shown statistically significant improvement in subjective and objective voice measures, as well as laryngeal stroboscopy findings after treatment. The pulsed dye and other lasers have shown effectiveness and potential in treating cutaneous and vocal scarring.

Two-step selective photoionization of lithium isotopes is carried out in a hollow cathode (HC) discharge lamp using a nitrogen-laser-pumped homemade tunable dye laser (∼0.2 cm-1, 7ns, 640-680nm). The HC lamp is developed in-house and used as a lithium ion source as well as a detector. The dark space region of HC discharge is illuminated by a dye laser exciting pulse followed by an ionizing radiation from the nitrogen laser. The high electric field (∼kV/cm) present in HC dark space is exploited for fast charge collection, produced by the simultaneous interaction of exciting and ionizing laser beams with sputtered lithium atoms, enabling the detection of photoionization signal. Photoionization signals with a high signal-to-noise ratio are obtained without using any amplifier. Effects of the ionizing laser pulse energy and the precise tuning of the dye laser on lithium photoionization signal, across 670.780nm (S1/22→P1/2,3/22) transition, are studied. The fine structure of lithium is clearly identified, and its two isotopes (Li7,6) are fairly resolved in the measured photoionization spectrum. Using a saturation technique, the photoionization cross section and the number density of lithium atoms for the Li7 (P3/22) excited level are also measured as 18.5±2.4 Mb, N0∼1.7×109 (atoms/cm3). The results obtained infer that HC-lamp-based photoionization is an easier and cost-effective way of selective photoionization of lithium atoms, and it can be applied for other elements also.

Open AccessCCS ChemistryRESEARCH ARTICLE1 Jan 2022An Optically Reconfigurable Förster Resonance Energy Transfer Process for Broadband Switchable Organic Single-Mode Microlasers Chan Qiao, Chunhuan Zhang, Zhonghao Zhou, Jiannian Yao and Yong Sheng Zhao Chan Qiao Key Laboratory of Photochemistry, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 University of Chinese Academy of Sciences, Beijing 100049 , Chunhuan Zhang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory of Photochemistry, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 , Zhonghao Zhou Key Laboratory of Photochemistry, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 , Jiannian Yao Key Laboratory of Photochemistry, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 University of Chinese Academy of Sciences, Beijing 100049 and Yong Sheng Zhao *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory of Photochemistry, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 University of Chinese Academy of Sciences, Beijing 100049 https://doi.org/10.31635/ccschem.021.202000768 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Miniaturized lasers with multicolor output and high spectral purity are indispensable for various ultracompact photonic devices. Here, we propose an optically reconfigurable Förster resonance energy transfer (FRET) process to realize broadband switchable single-mode lasing based on in situ activation of acceptors. The stoichiometric ratio of the donor and acceptor in the ready-made microstructures could be modulated readily by precisely activating the acceptors through a photoisomerization process, leading to a reconstructed FRET process to achieve dynamically switchable lasing. Furthermore, dual-color switchable single-mode lasing was realized by selectively constructing the FRET process in an identical coupled microdisks system. These results advance a comprehensive understanding of excited-state dynamics in organic composite material systems, thereby providing new ideas for the rational design of miniaturized photonic materials and devices with desired performances. Download figure Download PowerPoint Introduction Micro-/nanolasers regarded as the key driver for various applications ranging from biochemical sensors to on-chip optical interconnects have already been a subject of great interest.1–5 The synchronous achievement of monochromaticity and multiwavelength switching is an essential requirement of miniaturized lasers for realizing more versatile integrated photonic elements.6–11 Organic optofunctional materials, with abundant energy levels and excited-state processes,12–17 provide an ideal platform to achieve multiwavelength switchable lasing.18–20 Nevertheless, owing to the limited bandgap in a single gain medium, broadly tailoring the lasing wavelength of these materials remains a considerable challenge, which largely restricts their applications in ultracompact photonic devices. Therefore, it is critical to expand the gain region to enable widely switchable lasing for achieving broadband single-mode laser switch toward practical photonic integration. Förster resonance energy transfer (FRET) process, featuring an energy transfer from donor to acceptor, has been widely used to extend the gain range for broadband lasing.21,22 The output wavelength of FRET lasing could be tailored by modulating the FRET efficiency (ΦFRET), which is related to the stoichiometric ratio of donor and acceptor.23–27 However, due to the fixed concentration of laser dyes in a ready-made system, the ΦFRET is usually constant, almost precluding the possibility of in situ modulation of laser output. The reversible photoisomerization process generally leads to a dynamically tunable concentration of the isomers,28,29 promising for modulating the stoichiometric ratio of donor and acceptor in ready-made systems.30 Moreover, the isomers of spiropyran derivatives have been reported to fulfill optical gain for laser generation.31,32 Therefore, introducing such photochromic molecules into a donor–acceptor system is a potential for realizing an optically controlled FRET process, which is essential for multicolor switchable single-mode microlasers. Herein, we demonstrate the realization of broadband switchable single-mode microlasers based on an optically reconfigurable FRET process. A typical laser dye and photochromic compound were chosen to construct a FRET system, whereby the excitation energy of the donor dye could efficiently transfer to the isomer of the photochromic molecules. Based on the controlled photoisomerization process, the stoichiometric ratio of the donor and acceptor was tuned precisely through in situ activation of acceptors, resulting in an optically controllable ΦFRET for the tailorable gain region. Laser oscillation was further achieved by incorporating these dye molecules into polymeric microcavities. The emission output of the dual-color microlasers was finely controlled by optically reconfiguring the FRET process in the composite system. On this basis, through selective activation of the FRET process in the coupled microdisks, we constructed a heterogeneous coupled cavity system and achieved broadband switchable single-mode lasing. These results provided a comprehensive understanding of excited-state dynamics in organic composite materials and enlightened the rational design of miniaturized photonic materials and devices with desired performances. Experimental Method Synthesis of model compounds The model compound oligo-(α-phenylenevinylene)-1,4-bis(R-cyano-4-diphenylaminostyryl)-2,5-diphenylbenzene (referred to as OPV) used in this study was synthesized using the Knoevenagel condensation reaction ( Supporting Information Figure S1). Step 1: Synthesis of [1,1′;4′,1″]terphenyl-2′,5′-dicarbaldehyde A mixture of 2,5-dibromobenzene-1,4-dicarbaldehyde (1.0 g), phenylboronic acid (1.1 g), Pd(PPh3)4 (0.2 g), toluene (12.5 mL), and 2 M Na2CO3 solution (2.5 mL) was refluxed at 85 °C for 36 h under nitrogen, then poured into water and extracted using dichloromethane.33 The organic layer was washed with brine and water and dried over MgSO4. Next, the crude product was purified by flash column chromatography with dichloromethane as an eluent. After recrystallization from chloroform, the compound was obtained in 81% yield. Step 2: Synthesis of 2-(cyanomethyl)-4-(diphenylamino)benzene 2-(Cyanomethyl)-4-(diphenylamino)benzene was prepared from 4-(diphenylamino)benzaldehyde upon treatment with tosylmethylisocyanide (TosMIC) and tBuOK in a single step.34 Step 3: Synthesis of OPV [1,1′;4′,1″]terphenyl-2′,5′-dicarbaldehyde (0.1 mmol) and 2-(cyanomethyl)-4-(diphenylamino)benzene (0.21 mmol) were dissolved in tert-butanol (1.2 mL) and tetrahydrofuran (THF; 0.8 mL) under nitrogen atmosphere.35 Potassium tert-butoxide (0.02 mmol) and tetra-n-butylammonium hydroxide (0.02 mmol, 1 M solution in methanol) were added quickly; then the mixture was stirred vigorously at 50 °C. After 20 min, the mixture was poured into acidified methanol. Next, the crude product was precipitated from methanol and further purified by column chromatography in darkness to obtain OPV. Preparation of microcavity We began the fabrication process by spin-coating a 2-μm thick layer of lift-off resist (LOR)-5A on a clean silicon substrate. To remove the solvent and ensure a clear interface, the first LOR-5A film was baked at 180 °C for 5 min. Then a 1.5-μm thick layer of poly(methyl methacrylate) [PMMA; molecular weight (MW) 996 K] was spin-coated on the top of the LOR layer, followed by soft baking at 180 °C for 2 min to remove the residual solvent and ensure flatness and uniformity over the wafer. The microstructures were patterned on the surface of the prepared PMMA layer by electron beam direct writing (EBDW). Subsequently, an exposed PMMA was developed in a 1:3 mixture of methyl isobutyl ketone (MIBK) and isopropyl alcohol (IPA) at room temperature for 30 s, followed by a thorough rinse in IPA and blow-dried by compressed nitrogen gas, leaving circular microdisks on LOR-5A film. Subsequently, a 101 developer was chosen specifically for selective LOR-5A removal. As a result, the edges of the PMMA microdisks were equally undercut, leaving circular LOR pillars to support larger PMMA disks. Characterization of the dye-doped PMMA composite The absorption and fluorescence spectra were measured using Shimidazu UV-2600 spectrophotometer (Shimadzu Co., Tokyo, Japan) and Hitachi F-7000 (Hitachi, Tokyo, Japan), respectively. The time-resolved photoluminescence (TRPL) was measured using an Edinburgh FLS980 spectrofluorometer system equipped with EPLED-360 (Edinburgh Instruments Ltd., Kirkton Campus, Livingston, UK). The morphology of the PMMA microdisk was examined using scanning electron microscopy (SEM; FEI Nova NanoSEM450; ,Thermo Fisher Scientific, Lafayette, CO). Bright-field optical images and fluorescence microscopy images were taken using an inverted fluorescence microscope (Nikon Ti-U) with a mercury lamp (Nikon Corp., Tokyo, Japan). The lasing characteristics of the microdisks were investigated with a home-built far-field micro-photoluminescence (PL) system. The samples were excited locally by a focused 450 nm pulse laser beam (150 fs, 1 kHz). The spatially resolved spectra were measured with a monochromator (Princeton Instruments Acton SP 2300i, New Jersey) connected with an electron-multiplying, charge-coupled device (EMCCD; Princeton Instruments ProEM 1600B). Results and Discussion An optically reconfigurable FRET process in the OPV-BIPS system Figure 1a presents the working mechanism of the optically reconfigurable FRET process. Before exposure to UV light, there is no FRET process in the polymeric matrix doped with donor and spiropyran molecules, and only green emission from the donor could be observed (Figure 1a, left). As the exposure time increased, the colorless spiropyran molecules are activated and convert to their luminous isomers, which act as energy acceptors to the donors (Figure 1a, middle). This process would result in a dynamic tunable stoichiometric ratio between the donor and acceptor, triggering a reconstruction of the FRET process. After sufficient UV light exposure (Figure 1a, right), the spiropyran molecules transformed completely to their isomers, which finally led to a switch of gain region for broadband switchable lasing. Figure 1 | An optically reconfigurable FRET process in the OPV-BIPS system. (a) The working mechanism of optically reconfigurable FRET process in the OPV-BIPS system. (b) Normalized absorption (dashed line) and PL (solid line) spectra of OPV (green) and BIPS-MC (red). (c) PL spectra of OPV-BIPS-doped PMMA film with increasing exposure time to UV light. (d) PL decay profiles of OPV-BIPS-doped PMMA film monitored at 560 nm with increasing exposure time to UV light. (e) Corresponding PL decay time and ΦFRET of the dye-doped PMMA film. Error bars represent the standard deviation of five representative measurements. Download figure Download PowerPoint We selected 1′,3′-Dihydro-1′,3′,3′-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-(2H)-indole] (BIPS) as photochromic molecules, which could be transformed quantitatively to high luminous merocyanine (BIPS-MC) by light ( Supporting Information Figure S2).30 The OPV ( Supporting Information Figure S1) is a typical laser dye,35 chosen as the energy donor to constitute the FRET pair because its PL spectrum largely overlapped with the absorption band of BIPS-MC. PMMA was utilized as the polymeric matrix to incorporate the donor–acceptor pair due to its high materials compatibility and good optical transparency in the visible (vis) and near-infrared (NIR) spectral ranges.36 As shown in Supporting Information Figure S3, the absorption band of BIPS is spectrally separated from the PL spectrum of OPV, implying a negligible FRET process between OPV and BIPS. With increasing UV light exposure time, the BIPS molecules were activated and converted to BIPS-MC molecules with strong absorption in the OPV emission band (Figure 1b and Supporting Information Figure S4), which would result in an efficient FRET process. Accordingly, we prepared a PMMA film doped with a 1:1 ratio of OPV:BIPS, and the excitation spectrum of the composite clearly showed an energy transfer process from OPV to BIPS-MC ( Supporting Information Figure S5).23 As illustrated in Figure 1c, before exposure to UV light, the PL spectrum was dominated by the emission of OPV, which indicated the absence of FRET. As the exposure time was increased, a stronger emission was obtained from the acceptor, accompanied by a decreasing emission from the OPV molecules. After sufficient exposure to UV light, the PL spectrum was dominated by the emission of BIPS-MC, and the fluorescence from OPV molecules was well suppressed. This evolution of PL spectra implied the existence of an optically reconfigurable FRET process, leading to a UV exposure time-controlled fluorescence emission. In Figure 1d, the PL decay profiles of the composite system at ∼560 nm revealed a distinct decrease of donor lifetime with increasing UV light exposure time ( Supporting Information Table S1), indicating the occurrence of efficient energy transfer from donor to acceptor. The ΦFRET was estimated from the lifetime as ΦFRET = 1 − τ/τ0, where τ0 and τ are the average lifetimes of the donor in the absence and presence of the acceptor, respectively. The calculated ΦFRET was up to 45% after sufficient UV light exposure, accompanied by a decreasing donor lifetime from 2.63 to 1.47 ns (Figure 1e). This should be attributed to the decreasing donor–acceptor separation distance as the increasing acceptor activated by UV light. The dynamically controlled ΦFRET could be utilized to tailor the gain region of the composite systems, which is promising for broadband tunable lasing. Lasing characteristics of a single microdisk Benefiting from the outstanding processability of PMMA, the OPV-BIPS-doped PMMA film was readily processed into high-quality microresonators by an EBDW method ( Supporting Information Figure S6).37 The as-prepared microdisks showed homogeneous and switchable emissions ( Supporting Information Figure S7), indicating that the optically reconfigurable FRET processes were well-maintained in these microcavities. As shown in the SEM images, the obtained microdisk had perfect circular boundaries and ultra-smooth surfaces ( Supporting Information Figure S8), promising to serve as a high-quality whispering gallery mode (WGM) cavity to support laser oscillations ( Supporting Information Figure S9). The size of microdisks was readily controlled over a wide range ( Supporting Information Figure S10), which was crucial for optimizing laser performance. The optically pumped lasing was characterized on a home-built far-field micro-PL system ( Supporting Information Figure S11). When the microdisk was pumped by a pulsed laser beam (450 nm, 150 fs, and repetition rate of 1 kHz), a bright rim was observed at the outer boundary of the microdisk (Figure 2a, inset), demonstrating a total internal reflection of the emitted light along the edge of the microdisk. With increasing pump fluence, the PL intensity at ∼560 nm was amplified dramatically, manifesting the lasing action from the OPV molecules (Figure 2a). The corresponding emission intensity and full width at half maximum (FWHM) plots versus pump fluence are shown in Figure 2b, revealing a characteristic apparent knee points at the threshold of ∼6.0 μJ/cm2. This further confirmed the lasing action in the microdisk with a high quality (Q, defined as λ/FWHM) factor of 1268.38–40 The modulated lasing spectra presented an increasing mode number with increasing cavity diameter (Figure 2c). The mode spacing (Δλ) and the diameter (D) satisfy the equation λ2/Δλ = ngπD (λ is the light wavelength and ng is the group refractive index), which is in good accordance with the WGM resonance condition (Figure 2d).15,41 These microdisks exhibited no significant photodegradation over 105 laser pulses ( Supporting Information Figure S12), demonstrating the excellent stability of these microlasers. Figure 2 | Lasing characteristics of a single microdisk. (a) Lasing spectra of a single microdisk with increasing pump fluence without exposure to UV light. Inset: PL image of the pumped microdisk. The scale bar is 10 μm. (b) Plots of lasing intensity and FWHM as a function of pump fluence. (c) Lasing spectra of dye-doped microdisks with different sizes. (d) Relationship between λ2/Δλ (λ = 550 nm) and the diameter of the microdisk. Download figure Download PowerPoint Optically controlled FRET lasing of a single microdisk Benefiting from the optically reconfigurable FRET process, a dynamically switchable laser in these composite microdisks should be expected by in situ activating the acceptors with external stimuli. The schematic diagram of dynamically tunable FRET lasing is shown in Figure 3a. Upon UV light exposure, the BIPS molecules quantitatively transform into their highly emissive BIPS-MC isomers, which resulted in a robust energy transfer process to suppress donor lasing. Because the ΦFRET is tightly correlated with the acceptor concentration, the rising BIPS-MC concentration would significantly increase ΦFRET, leading to an increased population of acceptor excitons for enhanced acceptor lasing. In contrast, under vis light exposure, the decreased concentration of BIPS-MC resulted in a suppressed acceptor lasing. The laser output of the composite system could finally recover back to the initial state after sufficient exposure to vis light, which is potential to be utilized to switch the lasing wavelength between the donor and acceptor. Figure 3 | Optically controlled FRET lasing. (a) Schematic excited-state processes in a dynamically tunable FRET lasing system. (b) Lasing spectra of an identical [email protected] microdisk with increasing exposure time to UV light. Insets: corresponding PL images of the microdisk. The scale bar is 10 μm. (c) Corresponding lasing intensity at 562 nm (green) and 704 nm (red) with increasing exposure times to UV light. (d) Lasing spectra of an identical [email protected] microdisk under alternate irradiation with UV and vis light. Download figure Download PowerPoint The optically reconfigurable FRET lasing process was investigated in-depth in an identical microdisk under different UV light exposure times with fixed pump fluence. The respective doping concentrations of OPV and BIPS in PMMA were set at 10 wt % with a stoichiometric ratio of 1:1 ( Supporting Information Figure S13). Figure 3b depicts the dynamically tunable dual-color lasing from a well-fabricated microdisk. Before the exposure to UV light, the spectrum was dominated by donor lasing at the green wavelength (Figure 3b, bottom). As the exposure time increased, a strong acceptor lasing was observed, accompanied by a decrease in donor lasing, leading to a distinct color variation (Figure 3b, insets). After sufficient UV irradiation, the lasing spectrum was dominated by the acceptor, and lasing from OPV molecules was well-suppressed (Figure 3b, top, and Supporting Information Figure S14). The corresponding lasing intensities at the wavelength of 562 nm (OPV) and 704 nm (BIPS-MC) versus exposure time of UV light show that the laser output can be well controlled by dynamically reconfiguring the FRET process (Figure 3c). Benefiting from the excellent reversibility of photoisomerization processes, the lasing wavelength was fully recovered upon exposure to vis light (Figure 3d) with good reproducibility ( Supporting Information Figure S15). Optically switchable single-mode lasing in coupled microdisks The brand new mechanism showed great potential for building optically switchable single-mode lasers in coupled cavity systems based on spatially selective activation of acceptors by UV light (Figure 4a). Accordingly, coupled microdisk cavities doped with OPV-BIPS were constructed for single-mode lasing ( Supporting Information Figure S16),42 and bright fluorescence emissions were further observed under excitation ( Supporting Information Figure S17). Thus, after the activation of all acceptors in the coupled microdisks by UV light, the single-mode lasing λ1 would switch to a longer wavelength λ2 due to the shift of gain region. Based on spatially selective activation of the acceptor, a heterogeneous coupled microdisks system could be obtained, which is promising for supporting the sustained operation of dual-color single-mode laser λ1 + λ2.6 Figure 4 | Optically switchable single-mode lasing. (a) Schematic illustration of the optically controlled single-mode lasing in coupled microdisks. (b) Lasing spectra of the coupled microdisk with increasing pump fluence before exposure to UV light. Inset: PL image of the pumped microdisks. (c) Switchable dual-color single-mode lasing with an optically controlled FRET process. Insets: corresponding PL images of the coupled microdisks. (d) A plot of the lasing wavelength versus switching cycles. The scale bar is 10 μm. Download figure Download PowerPoint The exact observations from the experiments were as follows: (1) The lasing peak of the coupled microdisks was located at ∼558 nm before the exposure to UV light (Figure 4b and Supporting Information Figure S18), demonstrating a high quality (Q ∼1395) single-mode lasing action from the donor OPV. (2) Under homogeneous UV light exposure for 2 min, the total activation of the BIPS-MC molecules led to a complete reconfiguration of the FRET process, resulting in a switch from a single-mode lasing at 558 nm (Figure 4c, bottom) to acceptor lasing at 704 nm (Figure 4c, top, and Supporting Information Figure S19). (3) When one of the microdisks was exposed separately to UV light, red emission from the microdisk was observed while the other remained unchanged, manifesting the achievement of heterogeneous coupled structure for dual-wavelength single-mode lasing (Figure 4c, middle). Furthermore, the lasing spectral shift remained almost unchanged after dozens of continuous cycles (Figure 4d), indicating excellent stability and reliability of the switchable single-mode microlasers. This prototype illustrated the applicability of the optically reconfigurable FRET process in coupled microcavities for dual-color single-mode microlaser switches. Conclusion A broadband switchable single-mode microlaser was implemented based on an optically reconfigurable FRET process in OPV-BIPS-doped coupled microdisks. The photoisomerization process between BIPS and BIPS-MC was utilized to achieve a tunable acceptor concentration for dynamically tailoring the stoichiometric ratio of donor and acceptor, leading to a reconfiguration of FRET process. The output of dual-color microlasers was modulated precisely by optically reconstructing the FRET process. On this basis, multicolor switchable single-mode lasing was realized by selectively activating the FRET process in these coupled microdisks. These results inspired a more comprehensive understanding of the relationship between excited-state dynamics and photonic functions for the rational design of miniaturized photonic materials and devices with desired performances. Supporting Information Supporting Information is available and includes materials, synthesis of model compound, preparation of microcavity, characterizations, supporting figures S1–S19 and table S1, and references. Conflict of Interest There are no competing interests. Acknowledgments This work was supported financially by the Ministry of Science and Technology of China (grant no. 2017YFA0204502), the National Natural Science Foundation of China (grant nos. 21790364 and 51903238), the Postdoctoral Innovation Talent Support Project (grant no. BX20180314), the China Postdoctoral Science Foundation (grant no. 2019M650854).

Spectroscopy is one of the most powerful techniques to analyze light of astronomical objects. New instrumentation strives to extend high-precision spectroscopy from the optical to the near-infrared spectral range. This development is driven by research on cool low-mass stars and the search for low-mass extrasolar planets with the radial velocity technique. A crucial requirement for precise spectroscopic measurements is the wavelength calibration that maps the pixels of a spectrograph’s detector to the corresponding wavelengths. In the optical, hollow cathode lamps and gas absorption cells are established wavelength calibrators, but these techniques cannot be readily transferred to the near-infrared because they do not provide enough spectral lines over a broad spectral range. Many spectral lines in the near-infrared are present in discharge spectra of molecules, such as nitrogen or CN. In this thesis, I investigate whether discharge spectra of these two molecules are potential wavelength references for astrophysical spectrographs. An experimental setup with a microwave-induced plasma lamp has been constructed. Characteristics of this lamp are the electrodeless design and the relatively inexpensive equipment. The plasma is sustained within a sealed glass tube so that measurements can be repeated with the same gas mixture and gas pressure. In addition, the sealed cell allows for a compact setup with no requirements for gas supply during operation. Spectra of different gas discharges, using two sealed gas cells, are recorded with a high-resolution Fourier transform spectrometer. One cell is filled with pure nitrogen gas, while the second cell is filled with a gas mixture producing emission from CN molecules. In the context of wavelength calibration, the analysis of the spectra focuses on line density, relative line intensities, wavelength stability and aging behavior. The nitrogen discharge provides a spectrum with densely-spaced emission lines over the whole spectral range 4500-11000 cm^-1 (0.9-2.2 µm). In the spectrum of the second discharge cell, about 4500 lines of CN and about 26000 lines of molecular nitrogen are detected (4500-10000 cm^-1). Both species combined provide about four times more lines as uranium from hollow cathode lamps in this spectral range. The wavelength stability of the spectra is measured with a precision of about 1 m/s over 24 hours. These properties make the microwave-induced plasma lamp an interesting candidate for wavelength calibration of future high-resolution spectrographs. However, the number of spectral lines usable for calibration will be reduced due to inhomogeneities regarding line spacing and line intensities, depending on the characteristics of a spectrograph (e.g., resolution and detector response). The demonstrated operational time of a single gas cell is about 180 hours, which is about 4-6 times shorter than typical lifetimes of hollow cathode lamps. Application of the microwave-induced plasma lamp for astrophysics is not limited to the task of wavelength calibration. An example is the laboratory study of molecular spectra which can be used to analyze magnetic fields in cool stars. First measurements with the discharge lamp operated in a magnetic field are presented. A magnetic flux density of B = (0.130 +/- 0.003) T is determined using the Zeeman-splitting of three argon lines. Measurements of molecular species, such as CN, in a calibrated field could be used in the future to identify magnetically-sensitive lines and to determine Landé factors.

Tunable Lasers Handbook

The performance of dye lasers with excited singlet-state absorption (ESA) at the pump and the lasing wavelengths is analyzed for short pulse pumped systems in the medium range of pumping intensities. Analytical and numerical solutions are presented for a wide range of the variable parameters such as ESA cross sections, the cavity reflectivity, and the pumping intensity. An experiment is described for measuring ESA cross sections in the pumping as well as the lasing regions, and the results for rhodamine 6G and rhodamine B are given, showing that due to ESA, the effective gain of the laser will be much lower than that expected from previously published data on the stimulated emission cross sections.

Tin is the principal element of interest in the SPES ISOL facility, which is under construction at Legnaro INFN Laboratories. Atomic nuclei have a shell structure in which nuclei with "magic numbers" of protons and neutrons are analogous to the noble gasses in atomic physics. In particular, recent theoretical studies, reveal double-magic nature of radioactive 132Sn. For this reason the nuclear physics community demonstrated, in the last years, a huge interest to produce and study this radioactive neutron rich isotope. Experiments on Tin laser resonant ionization have been performed in the offline SPES laser laboratory to investigate the capability of the new home-made Time of Flight (ToF) mass spectrometer. Several three-step, two color ionization schemes have been tested by comparing fast and slow optogalvanic signals from a Tin Hollow Cathode Lamp (HCL) and Time of Flight signals from the spectrometer. By scanning the wavelength of one of the two dye lasers across the specific resonance, comparisons of ionization signals from both the ToF and the HCL have been made, finding perfect agreement. Furthermore, with the mass spectrometer, resolved peaks of all the natural Tin isotopes have been detected. The natural abundances extracted from these measurements are in agreement with the table values for Tin isotopes. This work, with comparison of OGE and ToF signals, confirm the fully functional SPES offline laser laboratory capability in order to develop scheme studies also for the other possible Radioactive Ion Beam (RIB) elements.

Sub-picogram detection of lead by non-flame atomic fluorescence spectrometry with dye laser excitation