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Up-conversion luminescence (UCL) spectra of fluorophosphate glasses doped with the pair of rare-earth ions (REIs) ytterbium (4%) and thulium (0.1%) excited by radiation of a diode laser operating in steady-state mode at wavelength 975 nm are studied. Each of the observed UCL bands is a result of manifestation of several up-conversion processes (UCPs) corresponding to luminescence of thulium ions from different excited states. These UCPs are characterized by different degrees of effective nonlinearity (EN). The effect of pump power on UCL spectra formed by UCPs with different ENs is studied. The possibility of separation of spectra corresponding to individual UCPs from the total experimentally measured UCL spectrum of fluorophosphate glass doped with the pair of REIs ytterbium (4%) and thulium (0.1%) is demonstrated. The separation is based on the calculation of the EN based on the dependences of the UCL on the excitation power.
Up-conversion (UC) luminescence of rare earth ions is a promising area of research in optics and laser physics. Continuous lasers are widely used to excite UC processes, but femtosecond lasers are also of interest for several applications involving UC processes. Femtosecond laser radiation provides a high peak power of excitation pulses [1, 2], which can lead to multi-photon excitation [2, 3] and decay [4] processes. Direct laser excitation of thulium ions due to absorption processes between its excited states, along with the energy transfer from ytterbium ions, makes it possible to control the temporal dynamics of UC processes. One can either enhance or suppress UC processes using coherent control methods [2, 4, 5]. Note that the analysis of the time-hierarchy of UC processes [6], occurring due to both single- and multiphoton laser excitation of thulium ions [4] and energy transfer between ytterbium and thulium ions [7], becomes much more complicated when excited by femtosecond radiation [4, 8].
The study of ultrafast events in nature, such as chemical reactions and charge transfer processes, requires the use of ultrashort light pulses to capture phenomena occurring on the femtosecond to attosecond timescales [1]. Various experimental methods have been developed to generate these pulses, including supercontinuum generation in gas-filled hollow-core fibers [2] and thin plates [3,4]. Thin plate supercontinuum generaion is particularly promising due to its simplicity and compact design. Previous studies have demonstrated single-cycle pulse generation using silicon dioxide (SiO2) plates and multiple plate arrangements [5]. In this work, we theoretically investigate supercontinuum generation using a thin lithium fluoride (LiF) plate and compare it with SiO2. Our simulations are based on the parameters of Laser Research Center amplifier system at the National University of Mongolia and aiming to identify the optimal conditions for generating ultrashort pulses with this setup.
Up-conversion luminescence (UCL) spectra of fluorophosphate glasses doped with the rare-earth ions Yb3+ with concentrations of 4% and Tm3+ with concentrations of 0.1% were investigated using continuous-wave excitation at 975 nm. For each of four observed UCL bands (near 350, 475, 650 and 800 nm) we observed spectrally overlapping contributions of several up-conversion processes corresponding to the luminescence from various excited states of Tm3+. These states are characterized by different degrees of effective nonlinearity, i.e., different numbers of absorbed photons required to excite these states by transferring energy from the donor Yb3+ ions by their relaxation transitions 2F5/2 -2F7/2. We also analyzed influence of the pumping power on the contributions to UCL spectra from excitation processes with various effective nonlinearities. We separated the overlapping spectra of compound up-conversion processes different in the degree of effective nonlinearity. Our separation method relies on the factorization of wavelength and pumping power dependencies of the components processes contributions to the total luminescence. The method is self-testing and robust with respect to noise and experimental imperfections. Separating nonlinear processes by pump power dependence means that the spectral components inference can be carried on without a-priori assumptions and/or some preliminary modelling with just a single sample by means of the pump power variation. This separation method is useful when researching nonlinear media aiming for properties necessary for particular applications in sensing/imaging, multi-photon absorption, metrology, etc.
The study of ultrafast events in nature, such as chemical reactions and charge transfer processes, requires the use of ultrashort light pulses to capture phenomena occurring on the femtosecond to attosecond timescales [1]. Various experimental methods have been developed to generate these pulses, including supercontinuum generation in gas-filled hollow-core fibers [2] and thin plates [3,4].
In this study, we report that the thermal treatment effects on the Raman and photoluminescence (PL) spectra of mono and few-layer MoS2 films by annealing in the vacuum and air at 300ºC, respectively. The MoS2 film samples were prepared on silicon substrate by exfoliating from a bulk MoS2 crystal with a micromechanical exfoliation. For characterization of structural properties of the MoS2 films and identification of the Raman active modes, Raman spectrometer equipped with a He-Ne laser source and an optical microscope has been used. The results show that the vacuum annealing 7L MoS2 decreases the Full Width at Half Maximum (FWHM) of the Raman active modes as E12g, A1g and the vacuum annealing 1L MoS2 increases the PL intensity and peak energy, for 60% and 13.3meV, respectively also air annealing bilayer MoS2 increased the PL intensity (IA) and peak energy (EA), respectively for 85% and 15.4 meV (3000C for 40 min). After thermal annealing (vacuum and air), we observe that the indirect bandgap of the few-layer MoS2 was changed.
2004 онд графены нэг атомын давхаргыг илрүүлсэнээс хойш сүүлийн 10-аад жилд хоёр хэмжээст материалын судалгаа эрдэмтдийн сонирхлыг татсаар байна. MoS2 нь олон үеэс тогтдог бөгөөд үеүүд нь хоорондоо Ван дер Ваальсын сул харилцан үйлчлэлээр, харин нэг үе доторхи Mo ба S нь ковалентын хүчтэй харилцан үйлчлэлээр холбогддог. MoS2 нь цул бүтэцтэй үед шууд биш шилжилттэй, хориотой зоны өргөн нь 1.2 эВ ба харин нэг үет бүтэцтэй байхад шууд шилжилттэй, хориотой зоны өргөн нь 1.8 эВ байдаг. Энэ өвөрмөц шинж чанартай холбоотойгоор 2 хэмжээст MoS2-ыг сүүлийн жилүүдэд наноэлектроник ба оптоэлектроникийн төхөөрөмжүүдэд хэрэглэх боломжтойг судлаачид харуулсаар байна. Энэ чиглэлийн судлаачдын үр дүнгээс үзэхэд том хэмжээтэй 1 болон олон үет молибдений дисульфидийг гарган авах, үеийн тоог тодорхойлох зайлшгүй шаардлага тулгардаг. Ийм учраас эдгээр асуудлыг шийдэхийн тулд судалгааны ажлын зорилгоо дараах байдлаар дэвшүүлсэн. Үүнд: 1. Механик хуулах аргаар боломжит том хэмжээтэй нэг болон олон үеүүдийг гарган авах оновчтой горимыг тогтоох, тэдгээрийн оптик болон электронон шинж чанарыг үеийн тооноос хамааруулан судлах 2. Раман спектроскоп болон Фотолюминесценцийн спектроскопийн хэмжилтийн үр дүнг боловсруулж, Раманы пикийн болон шууд шилжилтэд харгалзах А пикийн талбай үеийн тооноос хэрхэн хамаарах зүй тогтлыг тогтоох 3. Оптик микроскоп ашиглан молибдений дисульфидийн нэг болон олон үеүүдийн оптик ялгарал (contrast)-ыг тодорхойлж, үеийн тооноос хэрхэн хамаарахыг үнэлэх 4. Дулаан боловсруулалт молибдений дисульфидийн торын эвдрэл болон кристал бүтцэд хэрхэн нөлөөлөхийг судлах
2004 онд графены нэг атомын давхаргыг1 илрүүлсэнээс хойш сүүлийн 10-аад жилд хоёр хэмжээст материалын судалгаа эрдэмтдийн сонирхлыг татсаар байна. MoS2 нь олон үеэс тогтдог бөгөөд үеүүд нь хоорондоо Ван дер Ваальсын сул харилцан үйлчлэлээр, харин нэг үе доторхи Mo ба S нь ковалентын хүчтэй харилцан үйлчлэлээр холбогддог. MoS2 нь цул бүтэцтэй үед шууд биш шилжилттэй, хориотой зоны өргөн нь 1.2 эВ3 ба харин нэг үет бүтэцтэй байхад шууд шилжилттэй, хориотой зоны өргөн нь 1.8 эВ2,4 байдаг. Энэ өвөрмөц шинж чанартай холбоотойгоор 2 хэмжээст MoS2-ыг сүүлийн жилүүдэд наноэлектроник ба оптоэлектроникийн төхөөрөмжүүдэд хэрэглэх боломжтойг судлаачид харуулсаар байна. Цул молибдений дисульфидээс нэг болон олон үеүүдийг механик хуулах арга, химийн ууршуулалтаар гарган авах үндсэн 2 арга байдаг. Эдгээрээс бид механик хуулах аргыг сонгон авч туршилтаа хийсэн. Энэ аргаар гарган авах нь харьцангуй бага зардалтай боловч, нарийн нямбай ажиллагаа шаарддаг. Судлаачид механик хуулах аргаар дээжийг гарган авсан гэдэг боловч яаж хэрхэн гарган авах тухай дэлгэрэнгүй мэдээлэл байдаггүй. Дээж гарган авахад хамгийн гол нөлөөлөх зүйл бол суурийг (substrate) нарийн цэвэрлэх ажиллагаа чухал юм. Цахиурын оксидийг суурь болгон сонгон авч түүний цэвэрлэгээний олон янзын туршилтыг хийж гүйцэтгэсэн. Үүнд: зүсэж авсан сууриа сайтар цэвэрлэхийн тулд ацетон, изопропан, нэрмэл усанд хийж тухай бүрт нь 15 минут 40кГц-ийн давтамжтай хэт авианы вананд (давтамж чухал нөлөөтэй) цэвэрлэж дээж гаргаж авах нь илүү үр дүнтэй байсан. Дээжийг гарган авсны дараа цавуу болон бусад бохирдуулагчийг зайлуулахын тулд ацетон, изопропан, нэрмэл усанд хийж тус бүр нь 10 минут 400С-т халааж сайтар цэвэрлэсэн. Энэ нь дээжийг гарган авах оновчтой горим гэдгийг бидний олон удаагийн туршилт харууллаа.
In this study, we report that the thermal treatment effects on the Raman and photoluminescence (PL) spectra of mono and few-layer MoS2 films by annealing in the vacuum and air at 300ºC, respectively. The MoS2 film samples were prepared on silicon substrate by exfoliating from a bulk MoS2 crystal with a micromechanical exfoliation. For characterization of structural properties of the MoS2 films and identification of the Raman active modes, Raman spectrometer equipped with a He-Ne laser source and an optical microscope has been used. The results show that the vacuum annealing 7L MoS2 decreases the Full Width at Half Maximum (FWHM) of the Raman active modes as E1 2g, A1g and the vacuum annealing 1L MoS2 increases the PL intensity and peak energy, for 60% and 13.3meV, respectively also air annealing bilayer MoS2 increased the PL intensity (IA) and peak energy (EA), respectively for 85% and 15.4 meV (3000 C for 40 min). After thermal annealing (vacuum and air), we observe that the indirect bandgap of the few-layer MoS2 was changed.
Surface-plasmon resonance (SPR) effect in thin metal films is highly sensitive to the dielectric refractive index changes in the vicinity of metal interface and the conventional Kretschmann configuration has been widely used in the SPR measurement. In this work we have presented the thickness optimization for a monometallic plasmonic structure using the prism-based Kretschmann configuration in angular and spectral interrogation. He-Ne laser with wavelength of 632.8 nm as an optical source, a thin gold layer deposited onto the glass substrate and a BK7 glass prism were applied for this studies. Based on the numerical analysis with variation of metallic layer thickness, angle of incidence and wavelength we will obtain the resonance parameters, such as reflectivity and phase. Experimentally, the SPR spectra of a pure gold sensing surface has been studied. With functionalizing with specific antigen molecules on the surface of the gold layer, this optimized settings can be further used as biosensing purpose for detection of certain analytes.
The Kerr-lens mode-locking (KLM) is known as a suitable method for generation of femtosecond pulses and mode-locked Ti:sapphire laser is now widely used sources of stable, energetic femtosecond pulses. We will present the simulation of KLM in Ti:sapphire laser cavities with a folded-cavity four-mirror by applying the ABCD ray-tracing technique for a Gaussian beam. Simulations will be performed for an asymmetric resonator design. Based on the numerical analysis, we will find the optimum design parameters (slit position, gain cavity spacing, gain medium position) for KLM.
The Kerr-lens mode-locking (KLM) is known as a suitable method for generation of femtosecond pulses and mode-locked Ti:sapphire laser is now widely used sources of stable, energetic femtosecond pulses. We will present the simulation of KLM in Ti:sapphire laser cavities with a folded-cavity four-mirror by applying the ABCD ray-tracing technique for a Gaussian beam. Simulations will be performed for an asymmetric resonator design. Based on the numerical analysis, we will find the optimum design parameters (slit position, gain cavity spacing, gain medium position) for KLM.
Керр-линз мод синхронизация (КМС) известна как подходящий метод генерации фемтосекундных импульсов, а Ti: сапфировый лазер с синхронизацией мод в настоящее время широко используется в стабильных энергичных фемтосекундных импульсах. Мы представим моделирование КМС в резонаторах Ti: сапфирового лазера со свернутым резонатором, применяя метод трассировки лучей ABCD для гауссовского пучка. Моделирование будет работать для асимметричной конструкции резонатора. Будут обсуждаться синхронизация мод с жесткой апертурой и усиление мод с мягкой апертурой. На основе численного анализа мы найдем оптимальные параметры конструкции (положение щели, расстояние между полостями усиления, положение среды усиления) для КМС. Ключевые слова: Самофокусировка, Керр-линз, Чувствительность смещения.
Two different pump-probe (PP) setups were developed successfully with different femtosecond pulse lasers. Using a PP setup with an ultra-short pulse laser, the excitation of coherent phonons in GaAs was measured for a calibration and an accuracy test of the developed setup. The frequencies of the coherent phonon modes were in good agreement with reported values [1, 2]. The setups for ZnSe and GaAs were transmission and reflection–type, respectively. When using the ultra-short pulse laser, the signal in the PP experiment was measured by a balanced photo diode. In the other PP experimental setup, built to measure the transient transmittance of bulk ZnSe, the light source and detector differed from the previous PP setup. A strong pulse laser was successfully used for the spectrally resolved pump probe experimental setup. A broadband, high-resolution spectrometer (HR4000CG-UV-NIR) was used as the detector.
In this study, we demonstrate mono and a few-layered MoS2 samples on an SiO2(270 nm)/Si substrate from bulk MoS2 crystal by a micromechanical exfoliation technique. For unambiguous layer number identification, experiments have been carried out with a unified complementary approach based on optical microscopy, atomic force microscopy, resonant Raman spectroscopy, and photo-luminescence spectroscopy. The experimental analysis was carried out on a statistically significant of mono and a few-layered MoS2 flakes (from one to ten layers) on the SiO2(270 nm)/Si substrate. Identification of the MoS2 layer number based on a quantitative analysis of resonant Raman and PL spectra is proposed. Results showed that first, the Raman intensity area ratio of the MoS2 E1 2g, A1g and 2LA modes to that area of the Si substrate increased linearly with increasing number of layers of MoS2. Second, the normalized PL intensity area of the (A) peak decreased linearly with increasing number of layers of MoS2
