Laser Light Research Articles

Ca3Sc2Si3O12:Ce3+, Mn2+ phosphor ceramic: A promising color converter for full‐color laser lighting

AbstractPhosphor ceramics are considered to be promising color converters for high‐brightness laser lighting. However, current laser lighting usually suffers from a poor color rendering index (Ra ∼70) when using a single‐structured phosphor ceramic, due to the deficiencies in the cyan‐green and red components of the luminescence spectra. In this study, a series of Ca3Sc2Si3O12:Ce3+, Mn2+ (CSS:Ce3+, Mn2+) phosphor ceramics were prepared for the first time using a solid‐state reaction method. Based on the efficient energy transfer from Ce3+ to Mn2+ (with an energy transfer efficiency of ∼33.3%), these ceramics exhibit three distinct emission peaks appearing at 505, 580, and 680 nm, covering the cyan‐green, yellow, and deep red‐light regions, respectively. Additionally, the ceramics display excellent thermal stability, with a thermal quenching temperature (T0.5) exceeding 160°C. Finally, a laser lighting source was constructed by combining the CSS:Ce3+, Mn2+ ceramic with a blue laser diode. By optimizing the Mn2+ concentration, a tunable color from cyan‐green to white was achieved, and the resulting Ra and luminous efficacy of the white light were 86 and 65 lm/W, respectively. These results demonstrate that the CSS:Ce3+, Mn2+ phosphor ceramic is an excellent color converter for full‐color laser lighting.

Hydrothermal synthesis of carbon quantum dots from Citrus limetta peels: Exploration of pH sensing, non-hemolytic activity and thermoluminescent properties

This study introduces a novel hydrothermal green method for synthesized carbon quantum dots (CQDs) using dried powders of Citrus limetta peels as a carbon source. The synthesized CQDs were evaluated for their photothermal response, pH sensing under various conditions and biocompatibility through non-hemolytic activity. CQDs had low crystallinity and an average size of 3 nm, ranging from 1 to 6 nm. CQDs have biocompatible properties, which makes them suitable for developing pH sensors. The study also revealed that the temperature of CQDs increases up to 37 °C under laser light irradiation of 808 nm, which might have potential applications in the biomedical field.

Effect of linear antenna chemical vapor deposition process parameters on the growth of nanocrystalline diamond-on-GaN films

The present work will systematically study the effect of different linear antenna microwave plasma enhanced chemical vapor deposition (LACVD) processing parameters on the optimal deposition of the diamond films. The low pressure and low temperatures of LACVD growth conditions is expected to deposit diamond films on otherwise reactive gallium nitride (GaN) surfaces, without any intermediate nitride buffer layer. First, the distances between the quartz tube and the samples put on the stage are varied (3–15 cm), which has a direct impact on the substrate temperature (415°–300 °C). Thereafter, the microwave input power was also altered (1.5–2.8 kW) to attain low substrate temperatures. It was found that 300 °C is the temperature limit, which can be attained by heating only with microwave plasma when the substrates are kept farthest (15 cm) away from the liner antenna quartz tube. An additional heater was used under the stage for rapidly achieving such minimum substrate temperature of 300 °C. Substrate heater was used for efficient growth of the diamond phase while using pulse mode frequency of microwave power input for optimization of the diamond films. The microstructure (plate-like and cauliflower-like) of the deposited nanocrystalline diamond (NCD) films and the cross-sectional images for thickness measurements was observed under the scanning electron microscope and the elemental analysis of the film surfaces was done by electron diffraction spectroscopy. Moreover, the diamond film quality and crystallinity were evaluated by Raman spectroscopy with 488 nm laser light. Diamond-on-GaN film results were compared with conventional Si substrate. Different LACVD reactor parameters like, antenna to stage distances, microwave input power in continuous wave mode, and growth temperatures have significant impacts on the grown films, both in terms of their quality and microstructure. It was found that the optimum deposition of nanocrystalline diamond film on GaN substrates without its surface etching was possible, under pulse mode (20 kHz, 45 % duty cycle) with 2 kW average input microwave power.

Investigation on high-quality health laser light source based on the age of lighting users

Investigation on high-quality health laser light source based on the age of lighting users

Supermode lasing and light amplification in multicore bismuth-doped fiber

Multicore fibers are promising structures with specific light propagation properties, which can be managed to benefit several applications in optical communications, fiber lasers and amplifiers, high-resolution imaging, and fiber-based sensors. The current use of multicore fibers in laser technology is mainly focused on in-phase coherent beam combining in far-field regions (out-cavity) using bulk optical elements. However, this approach is challenging in terms of the power scalability of all-fiber lasers (intra-cavity), particularly with using low-gain media, where it is needed to provide mode-coupling (supermode propagation) stability along relatively long lengths. Here, we report a conceptual design and fabrication of a multicore bismuth-doped fiber that is capable of achieving light amplification and stable lasing in the E-telecom band inside the cavity using the supermode selection approach. By analysis of experimental and simulation data, it was found that the employment of the proposed design of a Bi-doped fiber provides a considerable advantage over the single-core fiber in terms of laser performance (output power, slope efficiency) in the cladding-pumped configuration. These results open up new opportunities for further advancement of the optical fiber technology towards efficient bismuth-doped fiber-integrated amplifiers and lasers for the O+E+S+C+L+U-telecom bands, which may find important applications, especially for the development of next-generation multiband optical transmission systems.

Gas detection using cavity-enhanced Raman spectroscopy with a bidirectional multi-pass cell and polarization beam-splitting optical path

We demonstrate a substantial enhancement of gas Raman scattering using a bidirectional multi-pass cavity CERS system, which incorporates a polarization beam-splitting optical path. The system design allows the laser light to traverse the multi-pass cavity for four specific trips, satisfying the need for quick detection of various gas components. Our gas detection experiments using multi-pass cavities with different times of reflection indicate that the addition of polarization beam-splitting optical path gives 1.5 to 1.68 times enhancement of Raman signal compared with that of the system without polarization beam-splitting. For the detection of CH4, a limit of detection of 1.66 ppm was achieved with our system using a multi-pass cell with 41 times of reflection and an integration time of 30s. Our proposed design, which integrates a bidirectional multi-pass cavity with polarization beam-splitting optical path, gives an economical multicomponent gas detection system and a valuable tool for guiding the design and precise alignment of these cavities. This system shows significant promise for applications in e.g. human breath and environmental monitoring.

An NIR-propelled janus nanomotor with enhanced ROS-scavenging, immunomodulating and biofilm-eradicating capacity for periodontitis treatment

Periodontitis is an inflammatory disease caused by bacterial biofilms, which leads to the destruction of periodontal tissue. Current treatments, such as mechanical cleaning and antibiotics, struggle to effectively address the persistent biofilms, inflammation, and tissue damage. A new approach involves developing a Janus nanomotor (J-CeM@Au) by coating cerium dioxide-doped mesoporous silica (CeM) with gold nanoparticles (AuNPs). This nanomotor exhibits thermophoretic motion when exposed to near-infrared (NIR) laser light due to the temperature gradient produced by the photothermal effects of asymmetrically distributed AuNPs. The NIR laser provides the energy for propulsion and activates the nanomotor's antibacterial properties, allowing it to penetrate biofilms and kill bacteria. Additionally, the nanomotor's ability to scavenge reactive oxygen species (ROS) can modulate the immune response and create a regenerative environment, promoting the healing of periodontal tissue. Overall, this multifunctional nanomotor offers a promising new approach for treating periodontitis by simultaneously addressing biofilm management and immune modulation with autonomous movement.

Singlet fission photovoltaic cells as dual-wavelength laser power converters compatible with highly efficient solar cells

I applied photovoltaic cells equipped with singlet fission (SF) of molecular systems to dual-wavelength laser power converters (DW-LPCs) that efficiently convert two laser lights of different wavelengths to electricity. When the SF-DW-LPC is illuminated by eye-safe laser light of 1470 nm wavelength emitted from a laser diode, a single photon is converted to a single carrier. On the other hand, a single high-energy photon emitted from a high-power and low-cost laser diode of 808 nm is converted to two carriers by SF owing to its endothermic feature, even though the photon energy is slightly lower than twice the fundamental energy gap. Furthermore, the SF-DW-LPC operates as a highly efficient solar cell. These functions are required for optical wireless power transmission to moving objects including electric vehicles and flying drones. I modeled the photovoltaic process with SF and evaluated the limiting conversion efficiencies by detailed-balance calculations. Conversion efficiencies of the SF-DW-LPC for these two laser lights are competitive with those of the conventional single-junction LPCs dedicated to these wavelengths, respectively. The efficiency under solar light is close to that of the optimally designed SF solar cell. Furthermore, the SF-DW-LPC outperforms other types of DW-LPCs designed on the basis of intermediate band, triplet–triplet annihilation, and multiple exciton generation solar cells. Endothermic SF and carrier/energy extraction into the neighboring acceptors have already been demonstrated. However, molecular systems that apply to 1470 nm have not yet been realized, which is the top-priority issue to be solved to realize highly efficient SF-DW-LPCs.

Specificity of DNA damage formation induced by femtosecond near-infrared laser filamentation in water

We investigated the deoxyribonucleic acid (DNA) damage induced by laser filamentation, which was generated by focusing femtosecond near-infrared Ti:Sapphire laser light in water at several repetition rates ranging from 1000 Hz to 10 Hz. Using plasmid DNA (pUC19), the single-strand break, double-strand break, nucleobase lesions, and the fragmented DNA were analyzed and quantified by agarose gel electrophoresis. Additionally, the H2O2 concentration after irradiation was determined. We observed that (1) the DNA damage per laser shot and (2) the enzyme-sensitive base lesions per total DNA damage decreased as the laser repetition rate increased. Furthermore, (3) extraordinarily short DNA fragments were likely to be produced, compared with those produced using X-rays, and (4) most OH radicals could be eliminated by recombination to generate H2O2, preventing them from damaging the DNA. The Monte-Carlo simulation of the strand break formation implies that the observed dependency of strand break efficiency on the laser repetition rate is mainly due to diffusion of DNA molecules. These findings quantitatively and qualitatively revealed that an intense laser pulse induces a specific DNA damage profile that is not induced by X-rays, a sparsely ionizing radiation source.

Comparison of Polysaccharide Profiles of Different Seaweeds Based on Ion Chromatography and Ultrahigh‐Performance Liquid Chromatography

ABSTRACTIn traditional Chinese medicine research, seaweeds used for drug and health food development mainly refer to Sargassum pallidum (Turn.) C. Ag. (SP) and Sargassum fusiforme (Harv.) Setch. (SF). In the Chinese Pharmacopoeia, polysaccharides are the main quality control indicators. The total sugar content is determined by the anthrone–sulfuric acid method to evaluate the quality of seaweeds. However, this method cannot reflect the structural characteristics of seaweed polysaccharides and cannot distinguish among different seaweed varieties. Given this, to comprehensively evaluate the quality of different seaweeds, this study conducted a thorough analysis of the primary structure of polysaccharides in 11 batches of SF and 7 batches of SP. The neutral sugar content was determined by the anthrone–sulfuric acid colorimetric method, weight average molecular weight (Mw) by high‐performance size exclusion chromatography coupled with multi‐angle laser light scattering and refractive index detector method, sulfate content by ion chromatography and monosaccharide composition by ultrahigh‐performance liquid chromatography method, while also using professional software for statistical and similarity analysis. The results showed significant differences (p < 0.05) in neutral sugar content and Mw between S. fusiforme polysaccharides and S. pallidum polysaccharides, which can be used to distinguish SF and SP. The monosaccharide composition fingerprint was analyzed using chemometric methods, and it was found that fucose and glucose could serve as differential markers to distinguish SF and SP. This study further deepens the understanding of polysaccharides in seaweeds and more comprehensively evaluates the quality of different seaweeds.

Bactericidal Effect of Different Photochemical-Based Therapy Options on Implant Surfaces-An In Vitro Study.

Objectives: Photochemical systems are frequently recommended as an adjuvant treatment option in peri-implantitis therapy. The aim of the present study was to evaluate the efficacy of these treatment options, as well as a novel curcumin-based option, in a biofilm model on implants. Methods: Eighty dental implants were inoculated with an artificial biofilm of periodontal pathogens and placed in peri-implant pocket models. The following groups were analyzed: I, photodynamic therapy (PDT); II, PDT dye; III, curcumin/DMSO + laser; IV, curcumin/DMSO only; V, dimethyl sulfoxide (DMSO) only; VI, photothermal therapy (PTT); VII, PTT dye; VIII, control. After treatment, remaining bacterial loads were assessed microbiologically using quantitative real-time polymerase chain reaction analysis. Results: The PDT, PTT, and DMSO treatment methods were associated with statistically significant (p < 0.05) improvements in germ reduction in comparison with the other methods and the untreated control group. The mean percentage reductions were as follows: I (PDT) 93.9%, II (PDT dye) 62.9%, III (curcumin/DMSO + laser) 74.8%, IV (curcumin/DMSO only) 67.9%, V (DMSO) 89.4%, VI (PTT) 86.8%, and VII (PTT dye) 66.3%. Conclusions: The commercially available PDT and PTT adjuvant treatment systems were associated with the largest statistically significant reduction in periopathogenic bacteria on implant surfaces. However, activation with laser light at a suitable wavelength is necessary to achieve the bactericidal effects. The use of curcumin as a photosensitizer for 445 nm laser irradiation did not lead to any improvement in antibacterial efficacy in comparison with rinsing with DMSO solution alone.

Unveiling the effect of Ce3+ doping concentration in YAG:Ce single crystals towards high luminance laser lighting

Doping concentration of a phosphor is key parameter, affecting multiple properties such as light absorption, quantum yield, luminescence decay, thermal conductivity, and thermal quenching, etc. These properties could directly influence the luminous efficacy, the saturation threshold, and the emitting area of the phosphor when irradiated by laser, thus determining the peak luminance of a phosphor-converted laser lighting device. But surprisingly no systematic investigation has been done to research the effect of phosphor doping concentration on the luminance performance of laser lighting. Here we report the YAG:Ce single crystal phosphors with different Ce3+-doping concentrations (between 0.05 at% and 0.30 at%) and thicknesses (0.15 mm–0.45 mm). The relationship between Ce3+ concentration, phosphor thickness, and the colorimetric/photometric parameters (luminous efficacy, luminous flux, luminance) are built and elucidated. It is found that the thinner sample with higher doping density tends to be saturated at lower laser power density (314.1 W/mm2) and the device shows lower luminance. This result is also verified by thermal simulation that the corresponding sample shows highest working temperature. Remarkably, the optimal sample with thickness of 0.45 mm and Ce3+ density of 0.30 at% presents a record high luminous exitance of 33414 lm/mm2 and a record high luminance of 10636 Mcd/m2, indicating potential for use in special lighting, projector, and optical communication fields.

Mid-Infrared Supercontinuum Generation in Highly Nonlinear Chalcogenide Fibers

Interest in mid-infrared broadband laser light sources has surged due to applications in trace gas detection, free-space communications, and countermeasures. Progress in supercontinuum generation leverages fiber-based near-infrared and bulk-optic mid-infrared pump sources. In this paper, the Generalized Nonlinear Schrödinger Equation has been solved, using the Split Step Fourier Method, to simulate the pulse propagation and mid-infrared supercontinuum generation, inside a fiber composed of highly nonlinear As2Se3/As2S3 chalcogenide glass. The effect of various parameters, including fiber nonlinearity, Group Velocity Dispersion (GVD), input power and pulse-width, anomalous and normal dispersion pumping regime, etc. on the output supercontinuum bandwidth has been extensively studied. A tapered chalcogenide fiber is modeled to facilitate continuous simultaneous modification of the GVD and the Kerr nonlinearity parameter. Pumping the waveguides with 230-fs secant pulses at a peak power of 4.2-kW yields a mid-IR supercontinuum extending from [Formula: see text] to [Formula: see text] micrometers.

Laser nanofabrication inside silicon with spatial beam modulation and anisotropic seeding

Nanofabrication in silicon, arguably the most important material for modern technology, has been limited exclusively to its surface. Existing lithography methods cannot penetrate the wafer surface without altering it, whereas emerging laser-based subsurface or in-chip fabrication remains at greater than 1 μm resolution. In addition, available methods do not allow positioning or modulation with sub-micron precision deep inside the wafer. The fundamental difficulty of breaking these dimensional barriers is two-fold, i.e., complex nonlinear effects inside the wafer and the inherent diffraction limit for laser light. Here, we overcome these challenges by exploiting spatially-modulated laser beams and anisotropic feedback from preformed subsurface structures, to establish controlled nanofabrication capability inside silicon. We demonstrate buried nanostructures of feature sizes down to 100 ± 20 nm, with subwavelength and multi-dimensional control; thereby improving the state-of-the-art by an order-of-magnitude. In order to showcase the emerging capabilities, we fabricate nanophotonics elements deep inside Si, exemplified by nanogratings with record diffraction efficiency and spectral control. The reported advance is an important step towards 3D nanophotonics systems, micro/nanofluidics, and 3D electronic-photonic integrated systems.

Enhanced radio-photodynamic therapy potential of advanced gold-based nanoclusters for breast cancer treatment.

The purpose of current study was to assess the impact of ALA-coated gold nanoclusters (Au NPs) on the combined therapeutic effects of radiotherapy (RT) and photodynamic therapy (PDT) on healthy MCF-10A and MCF-7 breast cancer cells. The Au NPs were covered with ALA using PEG polymer, resulting in the synthesis of Au@ALA NPs. The successful synthesis of the final NPs was confirmed through FTIR, XRD, TEM, and UV-Vis tests. MCF-10A and MCF-7 cell lines were treated with different concentrations of Au@ALA NPs and exposed to irradiation of 2 and 4Gy (using MV X-ray) and 630nm laser light irradiation. Cytotoxicity was assessed using a multifaceted approach involving the MTT assay, real-time PCR, and colony forming assay. The findings revealed that the damage inflicted by Au@ALA NPs on cancerous tissue was significantly greater than that on normal tissue. The cytotoxic effects of all experimental groups exhibited a direct correlation with increasing concentrations and radiation doses. The combination of Au@ALA NPs with RT doses of 2 and 4Gy resulted in a reduction in cell viability by a factor of 1.58 (P = 0.001) and 1.73 (P = 0.004), respectively. Furthermore, the simultaneous intervention of NPs with PDT and RT at doses of 2 and 4Gy led to a decrease in cell viability by a factor of 2.10 (P = 0.001) and 3.08 (P = 0.001) in turn. Furthermore, the real-time PCR and colonogenic assay results demonstrated that the combined treatment significantly increased phosphorylation of ATM and expression of TP53, indicating an adequate synergistic effect on breast cancer cells. The concurrent application of Au@ALA NPs in RT and PDT successfully enhanced the radiosensitization of breast cancer cells to megavoltage RT and PDT.

The effect of age on the attachment ability of stick insects (Phasmatodea).

Many insect species have found their way into ageing research as small and easy-to-keep model organisms. A major sign of ageing is the loss of locomotory functions due to neuronal disorders or tissue wear. Soft and pliable attachment pads on the tarsi of insects adapt to the substrate texture to maximize their real contact area and, thereby, generate attachment during locomotion. In the majority of stick insects, adhesive microstructures covering those pads support attachment. Stick insects do not molt again after reaching the imaginal stage; hence, the cuticle of their pads is subject to continuous ageing. This study aims to quantify how attachment ability changes with age in the stick insect Sungaya aeta Hennemann, 2023 and elucidate the age effects on the material and microstructure of the attachment apparatus. Attachment performance (adhesion and friction forces) on substrates with different roughnesses was compared between two different age groups, and the change of attachment performance was monitored extending over a larger time frame. Ageing effects on the morphology of the attachment pads and the autofluorescence of the cuticle were documented using light, scanning electron, and confocal laser scanning microscopy. The results show that both adhesion and friction forces decline with age. Deflation of the pads, scarring of the cuticle, and alteration of the autofluorescence, likely indicating stiffening of the cuticle, were observed to accumulate over time. This would reduce the attachment ability of the insect, as pads lose their pliant properties and cannot properly maintain sufficient contact area with the substrate.

Random lasers with controlled emission modes by colloidal semiconductor quantum dots coupled to plasmonic nanorod arrays

Random lasers based on scattering for light amplification have gained extensive attention due to their simple structures. Colloidal semiconductor quantum dots (CSQDs) are excellent candidates as active media for random lasing. However, achieving CSQDs-based random lasers is challenging because the non-radiative Auger recombination produces a remarkable carrier loss. Here, we report random lasers with low thresholds based on the CSQDs coupled to the plasmonic nanorod arrays. The random lasers result from the enhancing excitation and emission rates of the CSQDs through plasmon resonance energy transfer induced by the spectral overlap between the resonant cavity modes of the plasmonic nanorod arrays and the excitons of the CSQDs, which reduces the carrier loss and establishes the optical gain in the CSQDs. Moreover, the incoherent and coherent emission modes can be controlled by varying the filling configurations (i.e., full-filling and partial-filling) of the plasmonic nanorods embedded in anodic aluminum oxide templates. Consequently, the incoherent random laser with a threshold of 19.3 μJ/mm2 and coherent random lasers with a threshold of 13.5 μJ/mm2 are performed, respectively. The proposed system provides a feasible method for low-threshold CSQDs-based random lasers with controlled emission modes, showing a promising avenue for potential applications.

445nm Blue Laser for Cricopharyngeal Myotomy/Zenker's Diverticulotomy: Proof of Concept and Use.

Treatment for Zenker's diverticulum and cricopharyngeal dysfunction has evolved to include flexible endoscopic approaches. Currently, no flexible modalities combine the precision cutting of CO2 laser and the hemostasis of knife electrocautery. We present the first series describing fiber-based 445nm blue light (BL) laser for endoscopic cricopharyngeal myotomy/Zenker's diverticulotomy. We describe usage characteristics and laser parameters with rigid esophagoscopy to determine the feasibility of use with flexible endoscopy. Retrospective review and literature review. The first nine cases of endoscopic diverticulotomy (n = 5) and cricopharyngeal myotomy (n = 4) with BL were reviewed. Rigid exposure was achieved with the Dohlman Slimline diverticuloscope. Mean age was 75.6 years. Average diverticulum depth was 0.89 cm ±1.0 cm. Pulsed mode was used in seven cases with mean of 6.86 W, 54 ms pulse on, and 286 ms pulse pause and overall mean of 6.00 W and 405 J. Complete myotomy with intact buccopharyngeal fascia and without bleeding limiting view was achieved in all patients. One of two patients in whom continuous wave setting was used developed subcutaneous emphysema following vigorous cough on POD0; this resolved after 7 days nothing per oral (NPO). Eight patients were started on oral intake without evidence for leak. Pulsed mode with fiber-to-tissue contact provided effective muscle cutting without disruption of buccopharyngeal fascia. Literature review yielded three articles examining flexible approach with laser for Zenker's and none with BL. BL provides safe and effective fiber-based cutting and hemostasis in endoscopic cricopharyngeal myotomy/Zenker's diverticulotomy. Future use in flexible endoscopic approaches appears feasible, though continuous wave should be avoided. IV Laryngoscope, 2024.

Structured electrons with chiral mass and charge.

Chirality is a phenomenon with widespread relevance in fundamental physics, material science, chemistry, optics, and spectroscopy. In this work, we show that a free electron can be converted by the field cycles of laser light into a right-handed or left-handed coil of mass and charge. In contrast to phase-vortex beams, our electrons maintained a flat de Broglie wave but obtained their chirality from the shape of their expectation value in space and time. Measurements of wave function densities by attosecond gating revealed the three-dimensional shape of coils and double coils with left-handed or right-handed pitch. Engineered elementary particles with such or related chiral geometries should be useful for applications in chiral sensing, free-electron quantum optics, particle physics or electron microscopy.

Photodynamic Therapy in the Treatment of Cancer-The Selection of Synthetic Photosensitizers.

Photodynamic therapy (PDT) is a promising cancer treatment method that uses photosensitizing (PS) compounds to selectively destroy tumor cells using laser light. This review discusses the main advantages of PDT, such as its low invasiveness, minimal systemic toxicity and low risk of complications. Special attention is paid to photosensitizers obtained by chemical synthesis. Three generations of photosensitizers are presented, starting with the first, based on porphyrins, through the second generation, including modified porphyrins, chlorins, 5-aminolevulinic acid (ALA) and its derivative hexyl aminolevulinate (HAL), to the third generation, which is based on the use of nanotechnology to increase the selectivity of therapy. In addition, current research trends are highlighted, including the search for new photosensitizers that can overcome the limitations of existing therapies, such as heavy-atom-free nonporphyrinoid photosensitizers, antibody-drug conjugates (ADCs) or photosensitizers with a near-infrared (NIR) absorption peak. Finally, the prospects for the development of PDTs are presented, taking into account advances in nanotechnology and biomedical engineering. The references include both older and newer works. In many cases, when writing about a given group of first- or second-generation photosensitizers, older publications are used because the properties of the compounds described therein have not changed over the years. Moreover, older articles provide information that serves as an introduction to a given group of drugs.