Table of contents

We revealed experimentally and explained the generation of a second giant pulse at the neighboring longitudinal mode in an Nd:YLF Q-switched laser. The delay between two pulses was about 100 ns. Based on this effect, a new method of longitudinal mode selection was implemented.

Excited state absorption (ESA) is a process that occurs in many laser gain media and can significantly impact their efficiencies of operation. In this work we develop a model to quantify the effect of ESA at the pump wavelength on laser efficiency, threshold and heating. In an analysis based on the common end pumped laser geometry we derive solutions and analytical expressions that model the laser behaviour. From these solutions we discuss the main parameters affecting efficiency, such as the laser cavity loss, pump ESA cross section and stimulated emission cross section. Methodologies are described to minimise the impact of pump ESA, for example by minimising cavity loss. It is also shown that altering the pumping geometry can significantly improve performance by improved distribution of the population inversion. Double end pumping can approximately halve the effect of pump ESA compared to single end pumping, and side pumping also has the potential to arbitrarily reduce its effect.

We demonstrate the operation of a room-temperature, solid-state, broadly tunable Cr-doped CdSe single-crystal continuous-wave laser. Longitudinal pumping with a continuous-wave diode laser array at 1.94 μm produced a broadband output of 280 mW at 2.6 μm with an incident power slope efficiency of 12%. With an intracavity Brewster-cut CaF₂ prism, we tuned the Cr²⁺:CdSe laser from 2.45 to 3.06 μm with a resolution of 10 nm and an output power up to 55 mW.

We discuss a novel method for generating hyper-broadband mid-infrared (MIR) supercontinua (SC) with coherent bandwidth from ~2 μm to ~10 μm by using As₂Se₃ photonic crystal fiber (PCF) and a 4.1 μm pump with femtosecond (fs) Airy pulse profile. Our simulations confirm that, when pumping in the normal dispersion region, the deceleration and self-healing properties of the Airy pulse can suppress the incoherent noise in modulational instability (MI) induced SC generation and maintain the pulse coherence over a long propagation distance. We also find that fs Airy pulse can generate an MIR SC with a broader coherent bandwidth than these can be achieved with fs parabolic secant pulse.

We demonstrated an all-normal-dispersion Yb-doped mode-locked fiber laser based on tungsten disulphide (WS₂). The saturable absorbers (SA) were made by mixing WS₂ solution with polyvinyl alcohol (PVA), and then evaporated on a substrate. The modulation depth of the WS₂ film was 2.06% and the saturable optical intensity was 71.6 MW cm⁻². When the WS₂ film was inserted into the fiber laser, the mode-locked pulses with pulse width of 2.5 ns and repetition rate of 2.84 MHz were obtained. As the pump power increased to 350 mW, the maximum output power was measured to be 8.02 mW. To the best of our knowledge, this is the first time to realize mode-locked pulses based on WS₂-SA at 1 μm waveband.

We develop a quantum scattering model to describe the exciton transport through the Fenna–Matthews–Olson (FMO) complex. It is found that the exciton transport involving the optimal quantum coherence is more efficient than that involving classical behaviour alone. Furthermore, we also find that the quantum resonance condition is easier to be fulfilled in multiple pathways than that in one pathway. We then definitely demonstrate that the optimal distribution of the pigments, the multitude of energy delivery pathways and the quantum effects are combined together to contribute to the perfect energy transport in the FMO complex.

A 20 km/80 Gbps bidirectional passive optical network (PON) employing three-stage, injection-locked, 1.55 μm, vertical-cavity surface-emitting lasers (VCSELs), negative dispersion fibers (NDFs), and optical band-pass filters (OBPFs) is proposed and demonstrated. The three-stage injection-locked technique, which can greatly increase the frequency response of VCSELs, is thereby expected to provide excellent transmission performance in a bi-directional PON. To be the first one of employing directly modulated, three-stage injection-locked, 1.55 μm, VCSELs; NDFs; and OBPFs results in excellent bit error rate (BER) performance, and clear eye diagrams are obtained for 20 km/80 Gbps, bidirectional PON applications. Such a novel bidirectional PON provides the advantage of a communication link for high data rates that could accelerate bidirectional PON deployment.

A scheme for giant Kerr nonlinearity via tunneling in triangular triple quantum dot molecules is proposed. In such a system, the linear absorption and the Kerr nonlinearity depend critically on the energy splitting of the excited states and the tunneling intensity. With proper parameters, giant Kerr nonlinearity accompanied by vanishing absorption can be realized. The enhancement of Kerr nonlinearity is attributed to the interacting double dark resonances induced by the tunneling between the quantum dots, requiring no extra coupling laser fields.

In the letter we define the notion of a quantum resistant ($(\epsilon ,\delta )$-resistant) hash function which consists of a combination of pre-image (one-way) resistance (ε-resistance) and collision resistance (δ-resistance) properties.

We present examples and discussion that supports the idea of quantum hashing. We present an explicit quantum hash function which is 'balanced', one-way resistant and collision resistant and demonstrate how to build a large family of quantum hash functions. Balanced quantum hash functions need a high degree of entanglement between the qubits. We use a phase transformation technique to express quantum hashing constructions, which is an effective way of mapping hash states to coherent states in a superposition of time-bin modes. The phase transformation technique is ready to be implemented with current optical technology.

This paper is a report on the novel experimental method of the study of the thermodynamic parameters of thin aluminum films in the critical point region. The controlled supercritical state of aluminum is achieved for the first time as a result of the heating of these films by the absorption of the powerful nanosecond pulse of Q-switched Nd:YAG laser at the fundamental wavelength. The possibility is demonstrated to find simultaneously the temporal dependencies of the temperature, of the pressure and of the density of aluminum during the experiment with the thin aluminum films confined at both sides by the quartz glass substrates. These dependencies are obtained taking into account the nonlinear dependence on the incident laser intensity of the light reflection coefficient from the irradiated surface of aluminum. For the first time the thermodynamic cooling cycle of aluminum after its heating by the powerful nanosecond laser pulse is plotted in the space of variables' temperature—pressure and temperature—density that get into the supercritical region.

A novel approach to fabricating nanocomposites comprising inorganic nanoparticles embedded in an organic matrix is presented. Ultra-fast laser ablation of a titanium metal target in aqueous ε-caprolactam monomer solution is used to produce ultra-small TiO₂ nanoparticles and to simultaneously initiate the polymerization of the monomer without the use of chemicals. The spectroscopic analysis and TEM studies reveal the formation of an organic matrix and its conjugation to the nanoparticles' surface. The laser beam induces the formation of TiO₂ nanoparticles, which subsequently act as photoinitiators of the polymerization of ε-caprolactam upon absorbing the photon energy provided by the unfocused part of the beam. This work can open new pathways for cost-effective and environmentally friendly nanocomposite production, in one step.

We report a new method for glucose monitoring in blood tissue based on the autocorrelation function (ACF) analysis in Fourier domain optical coherence tomography (FD-OCT). We have determined the changes in OCT monitoring signals' depth to characterize the modulations in ACFs for quantitative measurements of glucose concentrations in blood. We found that an increase in the concentration of glucose in blood results in decreased OCT monitoring signal due to the increase in the refractive index of the media.

The dynamics of Tm³⁺ optical center formation with increasing thulium concentration and the influence of different optical centers on the fluorescence and laser properties of the 2 μm ³F₄–³H₆ transition under ~795 nm laser diode excitation is studied.

Raman spectroscopy (RS) was employed for human saliva biochemical analysis with the aim to develop a rapidly non-invasive test for acute myocardial infarction (AMI) detection. High-quality Raman spectra were obtained from human saliva samples of 46 AMI patients and 43 healthy controls. Significant differences in Raman intensities of prominent bands were observed between AMI and normal saliva. The tentative assignment of the observed Raman bands indicated constituent and conformational differences between the two groups. Furthermore, principal component analysis (PCA) combined with linear discriminant analysis (LDA) was employed to analyze and classify the Raman spectra acquired from AMI and healthy saliva, yielding a diagnostic sensitivity of 80.4% and specificity of 81.4%. The results from this exploratory study demonstrated the feasibility and potential for developing RS analysis of human saliva into a clinical tool for rapid AMI detection and screening.

We demonstrate a high-power red laser at 660.5 nm from intracavity frequency doubling of a diode-side-pumped 1321 nm Nd:LiYF₄ (Nd:YLF) ring laser in a LiB₃O₅ (LBO) crystal. The maximum average output power of the red laser is obtained to be 23 W with beam quality factor M²  =  1.3.

DNA as a genetic biomolecule is more commonly referred to in life sciences, genetics, and microbiology. With the development of 'DNA photonics', it has shown tremendous applicability as an optical and photonic material. In this letter, we introduce a novel dye PicoGreen as a lasing medium in which DNA not only acts as a host matrix but also functions as a fluorescence enhancer. A dramatic increase in the fluorescence led us to the observation of optical amplification in dye doped DNA thin films. We also indicate the possible tunability of the output emission in the green–yellow region. With the obtained results, we have enough reasons to lead to the development of DNA-based bio-lasers.

We present diode-pumped Yb:YVO₄/YVO₄ thin-disk Raman laser operation around 1120 nm. The thin-disk crystals, Yb:YVO₄, and the Raman crystal, YVO₄, are cut with 250 μm and 20 mm, respectively. In multimode configurations, up to 0.91 W of Raman laser output power and a maximum slope efficiency of 10% are demonstrated corresponding to a pump power of 10 W. A continuous wavelength tuning range of 54 nm from 1096 to 1150 nm with a maximum output power of 320 mW at 1126 nm is confirmed.

A cascade, diode-pumped, continuous wave (CW), dual-wavelength operation in a 0.5% Er³⁺:Y₂O₃ cryogenic ceramic laser is demonstrated for the first time. The laser operates on cascaded Er (⁴I_11/2  →  ⁴I_13/2  →  ⁴I_15/2) transitions and can deliver 24 and 13 W at 1.6 and 2.7 μm, respectively. The overall efficiency with respect to the absorbed ~980 nm power was 62%. This is, to our best knowledge, the first demonstration of an efficient, high power, cascade, erbium laser achieved in bulk solid-state lasers. The analysis of the output power, the laser's wavelengths and slope efficiency for each individual laser transition are presented for pure CW operation mode. Also presented are the temporal behaviors of each laser line as a function of pump pulse duration in the quasi-CW regime.

The photonic density of states (PDS) of eigen polarizations (EPs) in cholesteric liquid crystal (CLC) cells with a defect layer inside are calculated. The dependences for the PDS and light intensity in the defect layer on the parameters characterizing absorption and gain are obtained. We investigated the possibility of connections between the PDS and the density of the light energy accumulated in the system. The influence of the defect layer and CLC layer on the PDS are investigated. It is shown that the PDS is maximum when the defect is in the center of the system. We also showed that the subject system can work as a low threshold laser, a multi-position trigger, filter, etc.

We systematically investigated a laser diode (LD) pumped Nd:GYSO (Nd³⁺:Gd_0.6Y_1.4SiO₅) laser. The output power of the continuous wave laser was as high as 3.5 W with a slope efficiency of 31.8%. In the Q-switched operation; the laser exhibited dual-wavelengths output (1073.6 nm and 1074.7 nm) synchronously with a Cr⁴⁺:YAG as the saturable absorber (SA). Additionally, a passively mode-locked laser was demonstrated using a semiconductor SA mirror with a maximum average output power of 510 mW at a central wavelength of 1074 nm, while the pulse width of the laser was as short as 5 ps. Our experiment proved that the Nd:GYSO mixed crystal was a promising material for a solid-state laser.

A comparison of laser ablation by a train of picosecond pulses and nanosecond pulses revealed a difference in laser craters, ablation thresholds, plasma sizes and spectral line intensities. Laser ablation with a train of picosecond pulses resulted in improved crater quality while ablated mass decreased up to 30%. A reduction in laser plasma dimensions for picosecond train ablation was observed while the intensity of atomic/ionic lines in the plasma spectra was greater by a factor of 2–4 indicating an improved excitation and atomization in the plasma.

The action of the longitudinal magnetic field on the collision-induced stimulated photon echo formed on the transition with the angular momentum change ${{J}_{a}}=0\to {{J}_{b}}=1$ is studied theoretically. It is shown that this action depends essentially on the sign of the difference in the orientation $\Gamma_{b}^{(1)}$ and alignment $\Gamma_{b}^{(2)}$ relaxation rates of the excited level b. If $\Gamma_{b}^{(2)}>\Gamma_{b}^{(1)}$, then the echo intensity in a weak magnetic field increases with the increase in the magnetic field strength, while in the alternative case $\Gamma_{b}^{(2)}<\Gamma_{b}^{(1)}$ it decreases up to zero value. The formulae enabling the determination of the magnitude of the difference $\Gamma_{b}^{(1)}-\Gamma_{b}^{(2)}$ from the experimental study of the oscillations of the echo intensity with the increase in the magnetic field strength are obtained.