The instability and broad optical features of perovskites limit the full realization of their unique optoelectronic potential. In this study, a novel MAPbBr3@SWCNTs hybrid material is presented, in which methylammonium lead bromide perovskite (MAPbBr3) is successfully encapsulated in single-walled carbon nanotubes (SWCNTs), fabricated in the form of thin films. Encapsulation enables the formation of 1D perovskite structures with narrowband light-emission, confined within a protective carbon nanoshell. A thorough investigation is conducted into the hybrid material's structure, linear optical properties, ultrafast carrier dynamics, and THz conductivity. The encapsulation preserves the distinct characteristics of both MAPbBr3 and SWCNTs while introducing novel optoelectronic effects, including the tuning and spectral unification of perovskite photoluminescence (PL), as well as doping-induced modifications to SWCNT carrier relaxation dynamics. Furthermore, the observation of negative photoconductivity (NPC) response of MAPbBr3@SWCNTs thin films highlights the potential of this innovative material as a strong candidate for future energy-efficient photodetectors, optoelectronic switches, neuromorphic computing devices, photovoltaic enhancers, and flexible electronics.

The instability and broad optical features of perovskites limit the full realization of their unique optoelectronic potential. In this study, a novel MAPbBr 3 @SWCNTs hybrid material is presented, in which methylammonium lead bromide perovskite (MAPbBr 3 ) is successfully encapsulated in single‐walled carbon nanotubes (SWCNTs), fabricated in the form of thin films. Encapsulation enables the formation of 1D perovskite structures with narrowband light‐emission, confined within a protective carbon nanoshell. A thorough investigation is conducted into the hybrid material's structure, linear optical properties, ultrafast carrier dynamics, and THz conductivity. The encapsulation preserves the distinct characteristics of both MAPbBr 3 and SWCNTs while introducing novel optoelectronic effects, including the tuning and spectral unification of perovskite photoluminescence (PL), as well as doping‐induced modifications to SWCNT carrier relaxation dynamics. Furthermore, the observation of negative photoconductivity (NPC) response of MAPbBr 3 @SWCNTs thin films highlights the potential of this innovative material as a strong candidate for future energy‐efficient photodetectors, optoelectronic switches, neuromorphic computing devices, photovoltaic enhancers, and flexible electronics.

Artificial zero-dimensional quantum defects within single-walled carbon nanotubes hold immense promise for diverse optoelectronic applications such as bioimaging, near-infrared light emission, nanolasing, and single-photon generation. This study delves into the temporal behavior of excitons within oxygen-functionalized single-walled carbon nanotubes, employing ultrafast transient absorption spectroscopy. Our investigation unveils the emergence of functionalization-induced excitonic states, distinguished by a long-lasting induced transmittance signal. Remarkably, even at degree of functionalization, we observe a reduction in the lifetime of band-edge excitons. In contrast, the population dynamics of deep-band excitons exhibit resilience against low and moderate functionalization degrees, with a pronounced reduction manifesting only at high degrees of functionalization. Our findings align closely with a kinetic model that accounts for an additional relaxation channel prompted by functionalization. This empirical evidence provides a significant breakthrough, establishing that the formation of functionalization-induced excitonic states within oxygen-functionalized single-walled carbon nanotubes is a consequence of the diffusive trapping of free band edge excitons, while interaction of deep band excitons with oxygen defect sites rather yields in exciton recombination. These insights shed light on the intricate dynamics of excitons within single walled carbon nanotube with artificially embedded quantum defects, advancing our understanding and potential applications in the realm of optoelectronics.

Covalent functionalization of single-walled carbon nanotubes (SWCNTs) is a promising way to improve their photoluminescent (PL) brightness and thus make them applicable as a base material for infrared light emitters. We report as high as over two-fold enhancement of the SWCNT PL brightness by using oxygen doping via the UV photodissociation of hypochlorite ions. By analyzing the temporal evolution of the PL and Raman spectra of SWCNTs in the course of the doping process, we conclude that the enhancement of SWCNTs PL brightness depends on the homogeneity of induced quantum defects distribution over the SWCNT surface.

The main properties of halide perovskites useful for solar cells make them also attractive for terahertz (THz)applications. This class of materials, well studied in the optical range, remains much less studied in the THz range. Meanwhile, increasing the efficiency of pulsed terahertz sources and detectors due to more advanced designs or new materials is one of the main directions in the field of terahertz technologies. Here, room-temperature detection of THz pulses propagating in free space with unbiased halide perovskites is demonstrated. The ultrafast change of conductivity that occurs in single crystals and polycrystalline films of lead methylammonium halides excited by a femtosecond laser enables efficient coherent detection of THz radiation. The results demonstrate the viability of solution-processable halide perovskite for the fabrication of photoconductive THz detectors and the further development of scalable and cost-effective sensor manufacturing for THz time-domain spectroscopy, imaging, and other photonic THz devices.

A compact waveguide Tm:YAP laser with a pulse repetition rate of 8 GHz is developed. A controllable change in the intracavity loss provides continuous tuning of the central emission wavelength of the laser operating in the Q-switched mode-locking in the range from 1925 to 1950 nm, as well as makes it possible dual-wavelength lasing. The main approach of this study is the use of waveguide structures inside the Tm:YAP crystal and the saturable absorber based on graphene. This approach is universal for producing compact lasers with the gigahertz pulse repetition rate, operating in a wide spectral range.

In recent years, progress has been made in obtaining extremely short electromagnetic pulses up to singlecycle and unipolar half-cycle pulses. For pulses with such a dependence of the electric field strength on time, the behavior and properties of such radiation and its interaction with matter acquires a number of new features. For extremely short unipolar pulses an important role in the interaction with matter is played by the electric pulse area (the integral of the electric field strength over time at a given point in space). The review presents the latest theoretical and experimental results in the field of obtaining and interaction of extremely short pulses with extended resonant media and individual microobjects (atoms, molecules, nanostructures). The results of new publications are discussed, in which phenomena are predicted that arise during the coherent propagation of extremely short pulses in resonant media - self-compression and self-stopping of a pulse in a homogeneous medium. Particular attention is paid to the effect of ultrashort pulses on microobjects from the point of view of the recently introduced concept of "interference " of pulse areas (electrical area and envelope area). The research results presented in the review relate to a new direction in modern optics that has emerged recently - "Optics of unipolar and subcycle light ", which is becoming an actively developing area of modern physics.

Theoretical studies of graphene began long before the first real samples were obtained (Wallace, 1947). Calculations performed in the 1930s and 1940s showed that a free two-dimensional film must be thermodynamically unstable. For this reason monolayer structures were obtained only on the surface of bulk materials. The first steps to make single carbon layers were made in the 1960s and 1970s using the reduction of graphite oxide from colloidal solutions (Boehm et al., 1962a, b) and the method of chemical vapor deposition (CVD) of hydrocarbons on metal substrates (Eizenberg and Blakely, 1979) or on their carbides (Aizawa et al., 1990). It has been shown that a high-temperature treatment of silicon carbide with evaporation of silicon leads to the formation of carbon film, that is, the so-called epitaxial growth is realized (van Bommel et al., 1975; Forbeaux et al., 1998). However, in all the works listed above, carbon films with a thickness of at least 20–30 layers were obtained, which were not inherently graphene. A detailed review of early experiments on the preparation of thin graphite layers was given in Jang and Zhamu (2008).

A multi-wavelength compact ultrafast laser based on a single-mode waveguide inscribed in Nd:YAG and graphene saturable absorber is developed. By changing the pump parameters, we demonstrate single-, dual- and multi- wavelength mode-locking regimes. Accurate control of intracavity losses provides stable CW passive mode-locking at a wavelength of 1064 nm and dual-wavelength mode-locking at 1061 and 1064 nm with a pulse repetition rate of 9.5 GHz.

Hybrid organic–inorganic perovskites, while well examined for photovoltaic applications, remain almost completely unexplored in the terahertz (THz) range. These low-cost hybrid materials are extremely attractive for THz applications because their optoelectronic properties can be chemically engineered with relative ease. Here, we experimentally demonstrate the first attempt to apply solution-processed polycrystalline films of hybrid perovskites for the development of photoconductive terahertz emitters. By using the widely studied methylammonium-based perovskites MAPbI3 and MAPbBr3, we fabricate and characterize large-aperture photoconductive antennas. The work presented here examines polycrystalline perovskite films excited both above and below the bandgap, as well as the scaling of THz emission with the applied bias field and the optical excitation fluence. The combination of ultrafast time-resolved spectroscopy and terahertz emission experiments allows us to determine the still-debated room temperature carrier lifetime and mobility of charge carriers in halide perovskites using an alternative noninvasive method. Our results demonstrate the applicability of hybrid perovskites for the development of scalable THz photoconductive devices, making these materials competitive with conventional semiconductors for THz emission.

We investigated room-temperature pulsed lasing in heavily doped Fe:ZnSe single crystals. The active elements were pumped by a Q-switched Cr3+:Yb3+:Ho3+:YSGG laser operating at 2.87 μm. Our results show that the generation of short laser pulses has a deep high-frequency modulation associated with relaxation dynamics in Fe:ZnSe. The lasing regime obtained in this study provides a straightforward way to generate mid-IR single nanosecond pulses at moderate pump energies. Moreover, we found a relation between the lasing pulse duration and the concentration of Fe2+ doping ions, and we experimentally demonstrated pulse shortening in heavily doped active crystals. Single-pulse lasing with an FWHM pulse duration of ~2.8 ns was achieved in ZnSe crystals doped with 2.3 · 1019 cm-3 Fe2+ ions. The demonstrated single-pulse lasing regime is applicable for seeding high-power mid-IR laser systems.

We report the observation of Coulomb blockade in field electron emission (FE) from single-wall carbon nanotubes (SWCNTs), which is manifested as pronounced steps in the FE current-voltage curves and oscillatory variations in the energy distribution of emitted electrons. The appearance of the Coulomb blockade is explained by the formation of nanoscale protrusions at the apexes of SWCNTs due to the electric field-assisted surface diffusion of adsorbates and carbon adatoms. The proposed adsorbate-assisted FE mechanism is substantially different from the well-known resonant tunneling associated with discrete electronic states of adsorbed atoms. The simulations based on the Coulomb blockade theory are in excellent agreement with the experimental results. The SWCNT field emitters controlled by the Coulomb blockade effect are expected to be used to develop on-demand coherent single-electron sources for advanced vacuum nanoelectronic devices.

We demonstrate that predepositing a nanometrically thin nickel film on a dielectric surface is sufficient to transform an amorphous pyrolyzed photoresist film (PPF) into a graphitic film (GRF) enriched with nickel particles. The GRF shows 3 orders of magnitude higher carrier mobility than the amorphous PPF, whereas its electrical conductivity doubles after etching away the nickel remains. The pronounced 2D peak in the Raman spectrum, almost dispersionless absorbance in the spectral range of 750-2000 nm, and the saturable absorption coefficient indicate that GRF possesses a graphene-like band structure. The proposed cost-efficient and scalable synthesis route opens avenues toward fabrication of micron size patterned graphitic structures of any shape directly on a dielectric substrate. Having graphene-like transport and electrical properties at 20 times higher absorbance than the single-layer graphene, GRF is attractive for fabrication of fast modulators for optical radiation, bolometers, and other photonics and optoelectronic devices that require enhanced optical absorption.

This paper presents single-mode waveguide Nd:YAG laser passively mode-locked with graphene saturable absorber. Fine tuning of intracavity losses provides the possibility not only to adjust the mode-locking stability but also to controllably switch between single- and dual-wavelength operation.

Despite that significant efforts have been made in the development of time-integrated graphene-based detectors operating in vis/IR/THz ranges, little is known about coherent detection of THz pulses with graphene. To date only a few time resolved studies with on-chip detection schemes, which significantly limit the spectral range naturally provided by the gapless band structure of graphene, are known. Here we demonstrate free-space room-temperature detection of THz radiation in a wide spectral range with optically gated graphene. The detection principle is based on registration of the time-domain waveform of the THz field by measuring the hot-carrier photocurrent under THz pulse exposure in optically excited graphene using a pump probe scheme. The applied method is simple and robust, while the sensitivity and working range of the developed graphene-based detector are comparable and in some aspects outperform materials conventionally used for terahertz time domain spectroscopy based on electro-optic sampling and photoconductive antennas. In addition, we demonstrate that efficient coherent detection of terahertz radiation in a wide range to above 2 THz does not require highly crystalline, single-layer graphene but can be also realized with ultrathin graphite film, which is synthesized directly on an arbitrary dielectric substrate. Employment of such a material for fabrication of ultrafast terahertz detectors creates a versatile platform for the scalable production of wide-aperture photoconductive detectors applicable in spatially resolved time-domain terahertz spectrometers and visualizers.

Ultrashort-pulsed laser sources with repetition rates over 1 GHz are important for applications in telecommunications, frequency metrology and in fundamental physics. Here we present an approach to build-up compact ultrafast single-mode waveguide lasers with gigahertz repetition rate using graphene saturable absorber mirror (GSAM) as the output coupler [1, 2]. In particular, due to very efficient coupling of pump light into the femtosecond laser inscribed waveguide [3] and wavelength insensitive properties of graphene this approach demonstrates the possibility to achieve simultaneous generation of <; 20 picosecond pulses centered at 1061 and 1064 nm with 9.8 GHz repetition rate. Precise control of the intracavity dispersion and losses through the length of air-gap interferometer formed between the active medium and the GSAM allowed us to demonstrate the possibility of switching between single and dual-wavelength lasing and to adjust the stability of self-starting mode-locking at particular wavelength. However due to a constant trade-off between losses and dispersion compensation in the current scheme the CW mode-locking can be achieved only in a single-wavelength regime. We also demonstrated applicability of the developed laser as a tunable master-oscillator for fiber-based amplified laser systems and achieved 530 mW output power at 1061 nm using Yb-doped fiber amplifier. Our study open up new aspects of passive mode-locking in waveguide Nd:YAG lasers and demonstrates the compatebility of the developed device with the widely used fiber schemes.

We propose and demonstrate a scalable technique to grow a thin polycrystalline graphitic film directly onto a fused silica substrate. The technique is based on the pyrolysis of a photoresist in the presence of a sacrificial 10 nm thick nickel catalyst layer. The synthesized graphitic film with a thickness of about 50 nm possesses almost constant 40% absorptance over visual and near infrared spectral regions. By using Raman characterization, third harmonic generation spectroscopy, and the Z-scan technique we perform a comparative study of the films pyrolyzed with and without a Ni catalyst. We show that the amorphous carbon dominates the linear and nonlinear optical properties of the resist film pyrolyzed without the Ni catalyst. In contrast, in presence of a Ni catalyst layer, the pyrolysis leads to a graphitic film that demonstrates a strong saturable absorption behavior at 1550 nm wavelength and has a nonlinear refractive index comparable with that of graphene. Thus, the developed, transfer-free synthesis technique provides an alternative route towards the controllable growth of wafer scale graphitic films on the dielectric substrates for photonics applications.

A passive mode locking Nd:YAG waveguide laser with a gigahertz pulse repetition rate is presented. Single-layer graphene is used as the saturable absorber. A tubular waveguide in the active medium was developed to provide generation of only the fundamental transverse mode. Due to this approach, stable generation of pulses with a duration of < 20 ps and a repetition rate of 9.8 GHz was achieved.