Picosecond optical pulses generation in a ring fiber laser with a semiconductor optical amplifier was investigated. Optical spectrum width is minimal at a fundamental resonant repetition frequency of 45 MHz, corresponding to a fiber resonator length of 4.5 m. As the frequency increases, the spectral width increases by an order of magnitude while the pulse duration decreases to 18 ps, and the power increases to 0.5 W. The power of picosecond optical pulses at the output of the semiconductor amplifier is 7 times higher than in the CW mode due to the carrier accumulation effect that occurs with short pump pulses.

Picosecond optical pulses generation in a ring fiber laser with a semiconductor optical amplifier was investigated. Optical spectrum width is minimal at a fundamental resonant repetition frequency of 45 MHz, corresponding to a fiber resonator length of 4.5 m. As the frequency increases, the spectral width increases by an order of magnitude while the pulse duration decreases to 18 ps, and the power increases to 0.5 W. The power of picosecond optical pulses at the output of the semiconductor amplifier is 7 times higher than in the CW mode due to the carrier accumulation effect that occurs with short pump pulses.

High-speed photodetectors (PDs) based on InGaAs/GaAs quantum well-dot (QWD) nanostructures with the frontal-end and back-end input of radiation have been studied. A PD with 40 rows of QWDs exhibited a spectral responsivity of up to 0.4 A/W in the 950–1100 nm optical range at a –5-V bias voltage. The decay time constant of pulsed response for PDs with an input area of 1.4 × 10 –4 cm 2 was ~250 ps.

A novel ultrasensitive transient time-resolved monitoring method has been developed suitable for studying of fast anisotropic relaxation in electronic excited states of polyatomic and biologically relevant molecules under excitation with femtosecond laser pulses. The method is based on the modulation of a pump beam polarization with a photo-elastic modulator and highly sensitive balanced detection of mutually orthogonal polarization components of a probe beam with following recording of the differential transient signal with a lock-in amplifier. The method was used for the study of anisotropic relaxation in the first electronic excited state of coenzyme NADH in solutions with various viscosity and polarity.

The mode of generation of picosecond optical pulses in the spectral range near 1064 nm by semiconductor lasers with distributed feedback and active region based on an InGaAs/GaAs quantum well has been studied. In the gain-modulation mode, the width of laser pulses decreases from 150 to 35 ps as the temperature increases from 5 to 50°C. It was demonstrated that there is a temperature range in which the pulse width is at a minimum, 35 ps, at a full spectrum width at half-maximum of 70 pm. The laser was mounted in a hermetically sealed butterfly case, which enabled a temperature tuning of the wavelength within 3 nm in the generation mode of pulses with width less than 45 ps. The peak output power was 0.4 W at the outlet of a single-mode fiber, with the polarization preserved.

We report on broad-area lasers, mode-locked lasers (MLLs), and superluminescent light-emitting diodes (SLDs) based on a recently developed novel type of nanostructures that we refer to as quantum well-dots (QWDs). The QWDs are intermediate in properties between quantum wells and quantum dots and combine some useful properties of both. 1.08 μm InGaAs/GaAs QWDs broad area edge-emitting lasers based on coupled large optical cavity waveguides show high internal quantum efficiency of 92%, low internal loss of 0.9 cm-1 and material gain of ~1.1∙104 cm-1 per one QWD layer. CW output power of 14.2 W is demonstrated at room temperature. Superluminescent light-emitting diodes with one QWD layer in the active region exhibit stimulated emission spectra centered at 1050 nm with the maximal full width at half maximum of 36 nm and the output power of 17 mW. First results on mode-locked operation in QWD lasers are also presented. 2 mm long two-section devices demonstrate the pulse repetition rate of 19.3 GHz and the pulse duration of 3.5 ps. The width of the radio frequency spectrum is 0.2 MHz.

Picosecond optical pulses generation by 1064nm InGaAs/GaAs quantum well distributed feedback lasers was investigated. In the gain-switching regime the duration of laser pulses decreased from 150 to 35 ps with temperature increase from 5 to 50 degrees. The minimal pulses duration 35 ps and spectral width 70 pm was achieved in the optimal temperature range. The laser was placed in sealed butterfly package, which made it possible to obtain wavelength temperature tuning of 3 nm where the pulses duration was less than 45 ps. The output peak power was 0.4 W from single-mode polarization maintaining fiber.

Исследованы быстродействующие фотодетекторы на основе InGaAs/GaAs-наноструктур квантовая яма-точки (КЯТ) с фронтальным и торцевым вводом излучения. Фотодетектор с 40 рядами КЯТ продемонстрировал спектральную чувствительность до 0.4 A/W в диапазоне 900-1100 nm при смещении -5 V. Постоянная времени спада импульсного отклика фотодетектора площадью 1.4·10-4 cm2 составила ~250 ps. Ключевые слова: фотодетектор, быстродействие, спектральная чувствительность, наноструктуры, емкость.

The paper presents an analysis of singlet oxygen phosphorescenceтkinetics in HeLa cells in suspension generated using Radachlorin photosensitizer. The characteristic time of singlet oxygen generation and its lifetime in cells have been determined. The experimental data analysis demonstrated that the singlet oxygen lifetime in cells decreases as compared to that in Radachlorin solutions in PBS and in water, while the lifetime of the photosensitizer triplet state increases.

The kinetics of singlet oxygen phosphorescence in HeLa cells suspended in phosphate buffered saline (PBS) being generated under photosensitized excitation with Radachlorin photosensitizer has been observed and studied. The characteristic time of singlet oxygen generation and its lifetime in HeLa cells have been determined. The experimental data analysis demonstrated that the singlet oxygen lifetime in cells decreases as compared to that in Radachlorin solutions in PBS and in water, while the photosensitizer triplet state lifetime increases.

AbstractWe present the results of an experimental study of two-section semiconductor lasers with active region consisting of three 3.1 nm InGaAs/InGaAlAs quantum wells. Passive mode-locking regime with a repetition rate of 10 GHz is realized. Different approaches have been compared to determine the stability of pulse repetition.

Люминесценция водного раствора фотосенсибилизатора Радахлорин при возбуждении в полосах 405 и 605 nm

Spectral characteristics of luminescence of the DMEM cell-culture medium are studied. The luminescence spectrum of the medium is determined in the visible and near-IR spectral ranges at wavelengths of up to 1350 nm under excitation at 405 and 660 nm. The lifetimes of excited states of the medium are determined, and the absence of singlet oxygen phosphorescence at about 1270 nm is demonstrated.

Entire luminescence spectrum of a commercial photosensitizer Radachlorin in aqueous solution has been recorded under laser excitation at 660 nm and analyzed. The peak of singlet oxygen phosphorescence at 1274 nm has been observed. The results obtained were compared with those recorded with laser excitation at 405 nm and reported earlier. The comparison showed the similarity of relaxation and luminescence processes occurring in both cases. Effective absorption cross sections were determined at each excitation wavelength, it was also shown that the singlet oxygen quantum yield is independent of photosensitizer concentration. The lifetime of the first excited triplet state in Radachlorin was determined. The results obtained can be used for optimization of the conditions of singlet oxygen generation and detection in solutions and biological samples.

Поступило в Редакцию 1 февраля 2018 г

AbstractWe have investigated two-sectional semiconductor lasers with an active region comprising five layers of InGaAs quantum dots, emitting in the spectral range near 1.06 μm. Regimes of passive mode-locking, passive Q-switching, and mode-locking with pulse modulated amplitude are realized. The transition conditions between generation regimes are investigated. The frequency tuning range with current increase in the Q-switched regime exceeds more than 4 times. The duration of the mode-locked pulses was 2 ps at the pulse repetition rate of 44.3 GHz.

We report results of spectral- and time-resolved study of Radachlorin photosensitizer luminescence in water in the spectral range of 950–1350nm and for determination of the photosensitizer triplet state and the singlet oxygen lifetimes responsible for singlet oxygen generation and degradation. At any wavelength within the explored spectral range the luminescence decay contained two major contributions: a fast decay at the ns time scale and a slow evolution at the μs time scale. The fast decay was attributed to electric dipole fluorescence transitions in photosensitizer molecules and the slow evolution to intercombination phosphorescence transitions in singlet oxygen and photosensitizer molecules. Relatively high-amplitude ns peak observed at all wavelengths suggests that singlet oxygen monitoring with spectral isolation methods alone, without additional temporal resolution can be controversial. In the applied experimental conditions the total phosphorescence signal at any wavelength contained a contribution from the photosensitizer triplet state decay, while at 1274nm the singlet oxygen phosphorescence dominated. The results obtained can be used for optimization of the methods of singlet oxygen monitoring and imaging.

The luminescence spectrum of aqueous solution of Radachlorin photosensitizer in the near IR spectral range (950-1350 nm) has been determined at the excitation in both the Soret and Q absorption bands. Major sources of the recorded luminescence were analyzed. Kinetics of photosensitizer and singlet oxygen phosphorescence signals were studied by means of time-resolved spectroscopy. The corresponding characteristic lifetimes were determined.

We have fabricated passive mode-locked laser diodes based on strained InGaAlAs/InGaAs/InP heterostructures with crystal lattice mismatch parameter of + 1.0 % between quantum well and barrier. The laser with temperature stabilization at 18 degrees C was demonstrated 10.027 GHz optical pulse repetition rate with 6 ps pulse duration time. Timing jitter of optical pulses in mode-locked regime was 0.145 ps.