Edik Rafailov - Academia.edu (original) (raw)

Papers by Edik Rafailov

ABSTRACT We present an overview of recent advances in generation of non-diffracting (Bessel) beam... more ABSTRACT We present an overview of recent advances in generation of non-diffracting (Bessel) beams from surface-emitting lasers, such as electrically and optically pumped VECSELs, and discuss their applications in optical trapping/tweezing and manipulation of micromachines. Our experiments on VECSEL-generated watt power level Bessel beams with central lobe diameters of a few to tens micrometers suggest that the semiconductor surface-emitting lasers are the best candidates for replacement of gas and solid-state counterparts for power-demanding applications in optical manipulation.

Optics Express, 2019

We report on conical refraction (CR) with low-coherence light sources, such as light-emitting dio... more We report on conical refraction (CR) with low-coherence light sources, such as light-emitting diodes and decoherentized HeNe laser radiation, and demonstrate different CR patterns. In our experiments, a variation of the pinhole sizes from 25 to 100 µm and the distances to pinhole from 50 to 5 cm reduced spatial coherence of radiation that resulted in the disappearance of the dark Poggendorff's ring in the Lloyd's plane. This is attributed to the interference nature of the Lloyd's distribution and found to be in excellent agreement with the paraxial dual-cone model of conical refraction.

SPIE Proceedings, 2015

Many applications of high-power laser diodes demand tight focusing. This is often not possible du... more Many applications of high-power laser diodes demand tight focusing. This is often not possible due to the multimode nature of semiconductor laser radiation possessing beam propagation parameter M 2 values in double-digits. We propose a method of 'interference' superfocusing of high-M 2 diode laser beams with a technique developed for the generation of Bessel beams based on the employment of an axicon fabricated on the tip of a 100 μm diameter optical fiber with highprecision direct laser writing. Using axicons with apex angle 140 0 and rounded tip area as small as ~10 μm diameter, we demonstrate 2-4 μm diameter focused laser 'needle' beams with approximately 20 μm propagation length generated from multimode diode laser with beam propagation parameter M 2 =18 and emission wavelength of 960 nm. This is a few-fold reduction compared to the minimal focal spot size of ~11 μm that could be achieved if focused by an 'ideal' lens of unity numerical aperture. The same technique using a 160 0 axicon allowed us to demonstrate few-μm-wide laser 'needle' beams with nearly 100 μm propagation length with which to demonstrate optical trapping of 5-6 μm rat blood red cells in a water-heparin solution. Our results indicate the good potential of superfocused diode laser beams for applications relating to optical trapping and manipulation of microscopic objects including living biological objects with aspirations towards subsequent novel lab-on-chip configurations.

IEEE Transactions on Biomedical Engineering

This paper presents clinical results of wireless portable dynamic light scattering sensors that i... more This paper presents clinical results of wireless portable dynamic light scattering sensors that implement laser Doppler flowmetry signal processing. It has been verified that the technology can detect microvascular changes associated with diabetes and ageing in volunteers. Studies were conducted primarily on wrist skin. Wavelet continuous spectrum calculation was used to analyse the obtained time series of blood perfusion recordings with respect to the main physiological frequency ranges of vasomotions. In patients with type 2 diabetes, the area under the continuous wavelet spectrum in the endothelial, neurogenic, myogenic, and cardio frequency ranges showed significant diagnostic value for the identification of microvascular changes. Aside from spectral analysis, autocorrelation parameters were also calculated for microcirculatory blood flow oscillations. The groups of elderly volunteers and patients with type 2 diabetes, in comparison with the control group of younger healthy volunteers, showed a statistically significant decrease of the normalised autocorrelation function in time scales up to 10 s. A set of identified parameters was used to test machine learning algorithms to classify the studied groups of young controls, elderly controls, and diabetic patients. Our conclusion describes and discusses the classification metrics that were found to be most effective.

IEEE Journal of Selected Topics in Quantum Electronics

In recent years, there has been increasing interest in the singlet form of oxygen as a regulator ... more In recent years, there has been increasing interest in the singlet form of oxygen as a regulator of the physiological functions of cells. The use of photosensitisers is a classical mechanism for the excitation of the main triplet form of oxygen and the generation of its singlet form. At the same time, it has been shown that there is a possibility of direct optical excitation of the main oxygen form into the singlet state by light at certain wavelengths. This review article aims to combine recent accumulated experience in the field of direct optical generation of singlet oxygen. We focus on works on the application of a 1267 nm wavelength, which is the most frequently used and well-studied in this area. In this review, we consider the use of laser-induced singlet oxygen in various biomedical applications both at the cellular level and at the level of whole organisms. This review presents the latest results on the use of singlet oxygen for therapeutic effects on cancer cells, as well as for photostimulation of neurons and the vascular and lymphatic systems.

IEEE Photonics Journal

Building upon recent advances in GaSb-based diode lasers and Er-doped fluoride fibre technologies... more Building upon recent advances in GaSb-based diode lasers and Er-doped fluoride fibre technologies, this article demonstrates for the first time the fibre-based amplification of midinfrared diode lasers in the wavelength range around 2.78 µm. The laser setup consists of a GaSb-based diode laser and a single-stage Er-doped fibre amplifier. Amplification is investigated for continuous wave (CW) and ns-pulsed input signals, generated by gainmodulation of the GaSb-based seed lasers. The experimental results include the demonstration of output powers up to 0.9 W, pulse durations as short as 20 ns, and pulse repetition rates up to 1 MHz. Additionally, the amplification of commercial and custom-made GaSb-based seed lasers is compared and the impact of different fibre end-cap materials on laser performance is analysed.

IEEE Journal of Selected Topics in Quantum Electronics

We present a prototype and verification of a multichannel laser system applicable to optogenetic ... more We present a prototype and verification of a multichannel laser system applicable to optogenetic research. In vivo photostimulation of neural cells expressing photoconvertible phytochromes or opsins requires enough light irradiation delivery to the brain that cannot be supported by continues-wave (CW) light sources. The use of ultra-short pulsed (USP) lasers operating in the second near-infrared region (II-NIR) and allowing nonlinear activation and deactivation of the photoactuators is a promising method that allows to increase the penetration depth and provide spatio-temporal localisation of radiation in tissues. This study aimed to investigate the efficiency of USP light propagation in the skin, skull, and brain of the mouse head, as well as to compare it with the corresponding CW radiation propagation in the 750-830 nm and 1086-1183 nm wavelength ranges. The experimental results and computer modelling demonstrate that about 10-12% of the initial laser radiation can reach the brain tissues. These results prove that under certain conditions, the USP laser radiation can reach a penetration depth with required power that will be sufficient for non-linear activation of opsins/phytochromes in the brain of living animals.

Terahertz Emitters, Receivers, and Applications XIII

IEEE Photonics Journal

We investigate the gain bandwidth and wavelengthtuning range of an erbium-doped fluoride fibre am... more We investigate the gain bandwidth and wavelengthtuning range of an erbium-doped fluoride fibre amplifier. The presented experimental setup consisted of a widely wavelengthtunable optical parametric oscillator (OPO), which was amplified in a single-stage Er-doped fluoride fibre amplifier. The OPO laser provided seed pulses with a pulse width of 5.2 ns and a repetition rate of 10 kHz. The fibre section consisted of 2.2 m of doubleclad, single-mode fibre with a doping concentration of 7 mol%. Wavelength-tuning was analysed at gain values of up to 26 dB and amplified pulse energies of up to 37.4 µJ. Using this setup, we demonstrate continuous wavelength tuning of more than 100 nm, covering the wavelength range from 2712 nm to 2818 nm.

Applied Sciences

Tunable metamaterials belonging to the class of different reconfigurable optical devices have pro... more Tunable metamaterials belonging to the class of different reconfigurable optical devices have proved to be an excellent candidate for dynamic and efficient light control. However, due to the consistent optical response of metals, there are some limitations aiming to directly engineer electromagnetic resonances of widespread metal-based composites. The former is accomplished by altering the features or structures of substrates around the resonant unit cells only. In this regard, the adjusting of metallic composites has considerably weak performance. Herein, we make a step forward by providing deep insight into a direct tuning approach for semiconductor-based composites. The resonance behavior of their properties can be dramatically affected by manipulating the distribution of free carriers in unit cells under an applied voltage. The mentioned approach has been demonstrated in the case of semiconductor metamaterials by comparing the enhanced propagation of surface plasmon polaritons w...

Conference on Lasers and Electro-Optics, 2020

We numerically investigate terahertz photoconductive antenna based on optimized plasmonic nanostr... more We numerically investigate terahertz photoconductive antenna based on optimized plasmonic nanostructures, stressing the stronger enhancement in case of transparent conducting oxide nanowires. The case is treated by means of local and nonlocal effective medium approximations.

Diagnostics, 2020

Abdominal cancer is a widely prevalent group of tumours with a high level of mortality if diagnos... more Abdominal cancer is a widely prevalent group of tumours with a high level of mortality if diagnosed at a late stage. Although the cancer death rates have in general declined over the past few decades, the mortality from tumours in the hepatoduodenal area has significantly increased in recent years. The broader use of minimal access surgery (MAS) for diagnostics and treatment can significantly improve the survival rate and quality of life of patients after surgery. This work aims to develop and characterise an appropriate technical implementation for tissue endogenous fluorescence (TEF) and assess the efficiency of machine learning methods for the real-time diagnosis of tumours in the hepatoduodenal area. In this paper, we present the results of the machine learning approach applied to the optically guided MAS. We have elaborated tissue fluorescence approach with a fibre-optic probe to record the TEF and blood perfusion parameters during MAS in patients with cancers in the hepatoduod...

Waves in Random and Complex Media, 2021

In this study, the models for the DNA origami lattice will be investigated. Our aim is to theoret... more In this study, the models for the DNA origami lattice will be investigated. Our aim is to theoretically explore the ways of constructing DNA origami. To achieve this goal the DNA origami structure, consisting of nanowires embedded in a host material, will be treated from the perspective of nanowire metamaterial. Surface plasmon polaritons propagating at the interface of air and DNA metamaterial are analyzed. The dispersion relation is attained using the transfer matrix technique and employing continuity conditions of electric fields and their derivatives at the boundary separating two regions. We have concluded that with numerous nanowires into the metamaterial unit, cell frequencies of surface plasmon polaritons are altered to higher frequencies. In this study, we have studied the effect of modifications of the metamaterial, allowing for the shift of the dispersion maps toward higher frequencies. It is possible to obtain the propagation of spoof plasmons mimicking the behavior of surface waves at lower frequencies. All the properties and parameters of the inorganic metamaterials are applicable to study the phenomenon of the organic substances

A conical refraction (CR) laser based on a separate gain medium (Nd:YVO4) and an intracavity CR e... more A conical refraction (CR) laser based on a separate gain medium (Nd:YVO4) and an intracavity CR element (KGW) was demonstrated. The decoupling of the gain and CR media enabled the laser to produce a well-behaved CR laser beam with excellent quality, while reducing the complexity of the pumping scheme. The proposed laser setup has the potential for power scaling using the efficient diode pumping approach and the properties of the generated CR beam are independent from the laser gain medium.

Biosensors, 2020

Novel, non-invasive wearable laser Doppler flowmetry (LDF) devices measure real-time blood circul... more Novel, non-invasive wearable laser Doppler flowmetry (LDF) devices measure real-time blood circulation of the left middle fingertip and the topside of the wrist of the left hand. The LDF signals are simultaneously recorded for fingertip and wrist. The amplitude of blood flow signals and wavelet analysis of the signal are used for the analysis of blood perfusion parameters. The aim of this pilot study is to validate the accuracy of blood circulation measurements recorded by one such non-invasive wearable LDF device for healthy young non-smokers and smokers. This study reveals a higher level of blood perfusion in the non-smoker group compared to the smoker group and vice-versa for the variation of pulse frequency. This result can be useful to assess the sensitivity of the wearable LDF sensor in determining the effect of nicotine for smokers as compared to non-smokers and also the blood microcirculation in smokers with different pathologies.

Progress in Quantum Electronics, 2017

For over half a century, laser technology has undergone a technological revolution. These technol... more For over half a century, laser technology has undergone a technological revolution. These technologies, particularly semiconductor lasers, are employed in a myriad of fields. Optical medical diagnostics, one of the emerging areas of laser application, are on the forefront of application around the world. Optical methods of non-or minimally invasive bio-tissue investigation offer significant advantages over alternative methods, including rapid real-time measurement, non-invasiveness and high resolution (guaranteeing the safety of a patient). These advantages demonstrate the growing success of such techniques. In this review, we will outline the recent status of laser technology applied in the biomedical field, focusing on the various available approaches, particularly utilising compact semiconductor lasers. We will further consider the advancement and integration of several complimentary biophotonic techniques into single multimodal devices, the potential impact of such devices and their future applications. Based on our own studies, we will also cover the simultaneous collection of physiological data with the aid a multifunctional diagnostics system, concentrating on the optimisation of the new technology towards a clinical application. Such data is invaluable for developing algorithms capable of delivering consistent, reliable and meaningful diagnostic information, which can ultimately be employed for the early diagnosis of disease conditions in individuals from around the world.

SPIE Proceedings, 2016

Here we overview our work on quantum dot based THz photoconductive antennae, capable of being pum... more Here we overview our work on quantum dot based THz photoconductive antennae, capable of being pumped at very high optical intensities of higher than 1 W optical mean power, i.e. about 50 times higher than the conventional LT-GaAs based antennae. Apart from high thermal tolerance, defect-free GaAs crystal layers in an InAs:GaAs quantum dot structure allow high carrier mobility and ultrashort photocarrier lifetimes simultaneously. Thus, they combine the advantages and lacking the disadvantages of GaAs and LT-GaAs, which are the most popular materials so far, and thus can be used for both CW and pulsed THz generation. By changing quantum dot size, composition, density of dots and number of quantum dot layers, the optoelectronic properties of the overall structure can be set over a reasonable range-compact semiconductor pump lasers that operate at wavelengths in the region of 1.0 µm to 1.3 µm can be used. InAs:GaAs quantum dot-based antennae samples show no saturation in pulsed THz generation for all average pump powers up to 1 W focussed into 30 µm spot. Generated THz power is superlinearly proportional to laser pump power. The generated THz spectrum depends on antenna design and can cover from 150 GHz up to 1.5 THz.

2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013

ABSTRACT We demonstrate an efficient THz source comprising an InAs quantum dot-based semiconducto... more ABSTRACT We demonstrate an efficient THz source comprising an InAs quantum dot-based semiconductor antenna optically pumped by a tunable dual-mode quantum-dot semiconductor laser, giving tunable CW THz output signal between around 250 GHz and 3 THz.

2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013

Here, we extend high peak power picosecond pulse generation to high repetition rates by employing... more Here, we extend high peak power picosecond pulse generation to high repetition rates by employing two monolithic tapered QD structures. The tapered mode-locked QD laser generates a pulse train at a repetition rate of 16 GHz with a pulse width of 1.15 ps at an average power of 6 mW. The active region of the novel tapered SOA structure consists of 15 InGaAs QD layers and the waveguide layout comprises two differently tapered sub-sections and a straight input section.

ABSTRACT We present an overview of recent advances in generation of non-diffracting (Bessel) beam... more ABSTRACT We present an overview of recent advances in generation of non-diffracting (Bessel) beams from surface-emitting lasers, such as electrically and optically pumped VECSELs, and discuss their applications in optical trapping/tweezing and manipulation of micromachines. Our experiments on VECSEL-generated watt power level Bessel beams with central lobe diameters of a few to tens micrometers suggest that the semiconductor surface-emitting lasers are the best candidates for replacement of gas and solid-state counterparts for power-demanding applications in optical manipulation.

Optics Express, 2019

We report on conical refraction (CR) with low-coherence light sources, such as light-emitting dio... more We report on conical refraction (CR) with low-coherence light sources, such as light-emitting diodes and decoherentized HeNe laser radiation, and demonstrate different CR patterns. In our experiments, a variation of the pinhole sizes from 25 to 100 µm and the distances to pinhole from 50 to 5 cm reduced spatial coherence of radiation that resulted in the disappearance of the dark Poggendorff's ring in the Lloyd's plane. This is attributed to the interference nature of the Lloyd's distribution and found to be in excellent agreement with the paraxial dual-cone model of conical refraction.

SPIE Proceedings, 2015

Many applications of high-power laser diodes demand tight focusing. This is often not possible du... more Many applications of high-power laser diodes demand tight focusing. This is often not possible due to the multimode nature of semiconductor laser radiation possessing beam propagation parameter M 2 values in double-digits. We propose a method of 'interference' superfocusing of high-M 2 diode laser beams with a technique developed for the generation of Bessel beams based on the employment of an axicon fabricated on the tip of a 100 μm diameter optical fiber with highprecision direct laser writing. Using axicons with apex angle 140 0 and rounded tip area as small as ~10 μm diameter, we demonstrate 2-4 μm diameter focused laser 'needle' beams with approximately 20 μm propagation length generated from multimode diode laser with beam propagation parameter M 2 =18 and emission wavelength of 960 nm. This is a few-fold reduction compared to the minimal focal spot size of ~11 μm that could be achieved if focused by an 'ideal' lens of unity numerical aperture. The same technique using a 160 0 axicon allowed us to demonstrate few-μm-wide laser 'needle' beams with nearly 100 μm propagation length with which to demonstrate optical trapping of 5-6 μm rat blood red cells in a water-heparin solution. Our results indicate the good potential of superfocused diode laser beams for applications relating to optical trapping and manipulation of microscopic objects including living biological objects with aspirations towards subsequent novel lab-on-chip configurations.

IEEE Transactions on Biomedical Engineering

This paper presents clinical results of wireless portable dynamic light scattering sensors that i... more This paper presents clinical results of wireless portable dynamic light scattering sensors that implement laser Doppler flowmetry signal processing. It has been verified that the technology can detect microvascular changes associated with diabetes and ageing in volunteers. Studies were conducted primarily on wrist skin. Wavelet continuous spectrum calculation was used to analyse the obtained time series of blood perfusion recordings with respect to the main physiological frequency ranges of vasomotions. In patients with type 2 diabetes, the area under the continuous wavelet spectrum in the endothelial, neurogenic, myogenic, and cardio frequency ranges showed significant diagnostic value for the identification of microvascular changes. Aside from spectral analysis, autocorrelation parameters were also calculated for microcirculatory blood flow oscillations. The groups of elderly volunteers and patients with type 2 diabetes, in comparison with the control group of younger healthy volunteers, showed a statistically significant decrease of the normalised autocorrelation function in time scales up to 10 s. A set of identified parameters was used to test machine learning algorithms to classify the studied groups of young controls, elderly controls, and diabetic patients. Our conclusion describes and discusses the classification metrics that were found to be most effective.

IEEE Journal of Selected Topics in Quantum Electronics

In recent years, there has been increasing interest in the singlet form of oxygen as a regulator ... more In recent years, there has been increasing interest in the singlet form of oxygen as a regulator of the physiological functions of cells. The use of photosensitisers is a classical mechanism for the excitation of the main triplet form of oxygen and the generation of its singlet form. At the same time, it has been shown that there is a possibility of direct optical excitation of the main oxygen form into the singlet state by light at certain wavelengths. This review article aims to combine recent accumulated experience in the field of direct optical generation of singlet oxygen. We focus on works on the application of a 1267 nm wavelength, which is the most frequently used and well-studied in this area. In this review, we consider the use of laser-induced singlet oxygen in various biomedical applications both at the cellular level and at the level of whole organisms. This review presents the latest results on the use of singlet oxygen for therapeutic effects on cancer cells, as well as for photostimulation of neurons and the vascular and lymphatic systems.

IEEE Photonics Journal

Building upon recent advances in GaSb-based diode lasers and Er-doped fluoride fibre technologies... more Building upon recent advances in GaSb-based diode lasers and Er-doped fluoride fibre technologies, this article demonstrates for the first time the fibre-based amplification of midinfrared diode lasers in the wavelength range around 2.78 µm. The laser setup consists of a GaSb-based diode laser and a single-stage Er-doped fibre amplifier. Amplification is investigated for continuous wave (CW) and ns-pulsed input signals, generated by gainmodulation of the GaSb-based seed lasers. The experimental results include the demonstration of output powers up to 0.9 W, pulse durations as short as 20 ns, and pulse repetition rates up to 1 MHz. Additionally, the amplification of commercial and custom-made GaSb-based seed lasers is compared and the impact of different fibre end-cap materials on laser performance is analysed.

IEEE Journal of Selected Topics in Quantum Electronics

We present a prototype and verification of a multichannel laser system applicable to optogenetic ... more We present a prototype and verification of a multichannel laser system applicable to optogenetic research. In vivo photostimulation of neural cells expressing photoconvertible phytochromes or opsins requires enough light irradiation delivery to the brain that cannot be supported by continues-wave (CW) light sources. The use of ultra-short pulsed (USP) lasers operating in the second near-infrared region (II-NIR) and allowing nonlinear activation and deactivation of the photoactuators is a promising method that allows to increase the penetration depth and provide spatio-temporal localisation of radiation in tissues. This study aimed to investigate the efficiency of USP light propagation in the skin, skull, and brain of the mouse head, as well as to compare it with the corresponding CW radiation propagation in the 750-830 nm and 1086-1183 nm wavelength ranges. The experimental results and computer modelling demonstrate that about 10-12% of the initial laser radiation can reach the brain tissues. These results prove that under certain conditions, the USP laser radiation can reach a penetration depth with required power that will be sufficient for non-linear activation of opsins/phytochromes in the brain of living animals.

Terahertz Emitters, Receivers, and Applications XIII

IEEE Photonics Journal

We investigate the gain bandwidth and wavelengthtuning range of an erbium-doped fluoride fibre am... more We investigate the gain bandwidth and wavelengthtuning range of an erbium-doped fluoride fibre amplifier. The presented experimental setup consisted of a widely wavelengthtunable optical parametric oscillator (OPO), which was amplified in a single-stage Er-doped fluoride fibre amplifier. The OPO laser provided seed pulses with a pulse width of 5.2 ns and a repetition rate of 10 kHz. The fibre section consisted of 2.2 m of doubleclad, single-mode fibre with a doping concentration of 7 mol%. Wavelength-tuning was analysed at gain values of up to 26 dB and amplified pulse energies of up to 37.4 µJ. Using this setup, we demonstrate continuous wavelength tuning of more than 100 nm, covering the wavelength range from 2712 nm to 2818 nm.

Applied Sciences

Tunable metamaterials belonging to the class of different reconfigurable optical devices have pro... more Tunable metamaterials belonging to the class of different reconfigurable optical devices have proved to be an excellent candidate for dynamic and efficient light control. However, due to the consistent optical response of metals, there are some limitations aiming to directly engineer electromagnetic resonances of widespread metal-based composites. The former is accomplished by altering the features or structures of substrates around the resonant unit cells only. In this regard, the adjusting of metallic composites has considerably weak performance. Herein, we make a step forward by providing deep insight into a direct tuning approach for semiconductor-based composites. The resonance behavior of their properties can be dramatically affected by manipulating the distribution of free carriers in unit cells under an applied voltage. The mentioned approach has been demonstrated in the case of semiconductor metamaterials by comparing the enhanced propagation of surface plasmon polaritons w...

Conference on Lasers and Electro-Optics, 2020

We numerically investigate terahertz photoconductive antenna based on optimized plasmonic nanostr... more We numerically investigate terahertz photoconductive antenna based on optimized plasmonic nanostructures, stressing the stronger enhancement in case of transparent conducting oxide nanowires. The case is treated by means of local and nonlocal effective medium approximations.

Diagnostics, 2020

Abdominal cancer is a widely prevalent group of tumours with a high level of mortality if diagnos... more Abdominal cancer is a widely prevalent group of tumours with a high level of mortality if diagnosed at a late stage. Although the cancer death rates have in general declined over the past few decades, the mortality from tumours in the hepatoduodenal area has significantly increased in recent years. The broader use of minimal access surgery (MAS) for diagnostics and treatment can significantly improve the survival rate and quality of life of patients after surgery. This work aims to develop and characterise an appropriate technical implementation for tissue endogenous fluorescence (TEF) and assess the efficiency of machine learning methods for the real-time diagnosis of tumours in the hepatoduodenal area. In this paper, we present the results of the machine learning approach applied to the optically guided MAS. We have elaborated tissue fluorescence approach with a fibre-optic probe to record the TEF and blood perfusion parameters during MAS in patients with cancers in the hepatoduod...

Waves in Random and Complex Media, 2021

In this study, the models for the DNA origami lattice will be investigated. Our aim is to theoret... more In this study, the models for the DNA origami lattice will be investigated. Our aim is to theoretically explore the ways of constructing DNA origami. To achieve this goal the DNA origami structure, consisting of nanowires embedded in a host material, will be treated from the perspective of nanowire metamaterial. Surface plasmon polaritons propagating at the interface of air and DNA metamaterial are analyzed. The dispersion relation is attained using the transfer matrix technique and employing continuity conditions of electric fields and their derivatives at the boundary separating two regions. We have concluded that with numerous nanowires into the metamaterial unit, cell frequencies of surface plasmon polaritons are altered to higher frequencies. In this study, we have studied the effect of modifications of the metamaterial, allowing for the shift of the dispersion maps toward higher frequencies. It is possible to obtain the propagation of spoof plasmons mimicking the behavior of surface waves at lower frequencies. All the properties and parameters of the inorganic metamaterials are applicable to study the phenomenon of the organic substances

A conical refraction (CR) laser based on a separate gain medium (Nd:YVO4) and an intracavity CR e... more A conical refraction (CR) laser based on a separate gain medium (Nd:YVO4) and an intracavity CR element (KGW) was demonstrated. The decoupling of the gain and CR media enabled the laser to produce a well-behaved CR laser beam with excellent quality, while reducing the complexity of the pumping scheme. The proposed laser setup has the potential for power scaling using the efficient diode pumping approach and the properties of the generated CR beam are independent from the laser gain medium.

Biosensors, 2020

Novel, non-invasive wearable laser Doppler flowmetry (LDF) devices measure real-time blood circul... more Novel, non-invasive wearable laser Doppler flowmetry (LDF) devices measure real-time blood circulation of the left middle fingertip and the topside of the wrist of the left hand. The LDF signals are simultaneously recorded for fingertip and wrist. The amplitude of blood flow signals and wavelet analysis of the signal are used for the analysis of blood perfusion parameters. The aim of this pilot study is to validate the accuracy of blood circulation measurements recorded by one such non-invasive wearable LDF device for healthy young non-smokers and smokers. This study reveals a higher level of blood perfusion in the non-smoker group compared to the smoker group and vice-versa for the variation of pulse frequency. This result can be useful to assess the sensitivity of the wearable LDF sensor in determining the effect of nicotine for smokers as compared to non-smokers and also the blood microcirculation in smokers with different pathologies.

Progress in Quantum Electronics, 2017

For over half a century, laser technology has undergone a technological revolution. These technol... more For over half a century, laser technology has undergone a technological revolution. These technologies, particularly semiconductor lasers, are employed in a myriad of fields. Optical medical diagnostics, one of the emerging areas of laser application, are on the forefront of application around the world. Optical methods of non-or minimally invasive bio-tissue investigation offer significant advantages over alternative methods, including rapid real-time measurement, non-invasiveness and high resolution (guaranteeing the safety of a patient). These advantages demonstrate the growing success of such techniques. In this review, we will outline the recent status of laser technology applied in the biomedical field, focusing on the various available approaches, particularly utilising compact semiconductor lasers. We will further consider the advancement and integration of several complimentary biophotonic techniques into single multimodal devices, the potential impact of such devices and their future applications. Based on our own studies, we will also cover the simultaneous collection of physiological data with the aid a multifunctional diagnostics system, concentrating on the optimisation of the new technology towards a clinical application. Such data is invaluable for developing algorithms capable of delivering consistent, reliable and meaningful diagnostic information, which can ultimately be employed for the early diagnosis of disease conditions in individuals from around the world.

SPIE Proceedings, 2016

Here we overview our work on quantum dot based THz photoconductive antennae, capable of being pum... more Here we overview our work on quantum dot based THz photoconductive antennae, capable of being pumped at very high optical intensities of higher than 1 W optical mean power, i.e. about 50 times higher than the conventional LT-GaAs based antennae. Apart from high thermal tolerance, defect-free GaAs crystal layers in an InAs:GaAs quantum dot structure allow high carrier mobility and ultrashort photocarrier lifetimes simultaneously. Thus, they combine the advantages and lacking the disadvantages of GaAs and LT-GaAs, which are the most popular materials so far, and thus can be used for both CW and pulsed THz generation. By changing quantum dot size, composition, density of dots and number of quantum dot layers, the optoelectronic properties of the overall structure can be set over a reasonable range-compact semiconductor pump lasers that operate at wavelengths in the region of 1.0 µm to 1.3 µm can be used. InAs:GaAs quantum dot-based antennae samples show no saturation in pulsed THz generation for all average pump powers up to 1 W focussed into 30 µm spot. Generated THz power is superlinearly proportional to laser pump power. The generated THz spectrum depends on antenna design and can cover from 150 GHz up to 1.5 THz.

2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013

ABSTRACT We demonstrate an efficient THz source comprising an InAs quantum dot-based semiconducto... more ABSTRACT We demonstrate an efficient THz source comprising an InAs quantum dot-based semiconductor antenna optically pumped by a tunable dual-mode quantum-dot semiconductor laser, giving tunable CW THz output signal between around 250 GHz and 3 THz.

2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013

Here, we extend high peak power picosecond pulse generation to high repetition rates by employing... more Here, we extend high peak power picosecond pulse generation to high repetition rates by employing two monolithic tapered QD structures. The tapered mode-locked QD laser generates a pulse train at a repetition rate of 16 GHz with a pulse width of 1.15 ps at an average power of 6 mW. The active region of the novel tapered SOA structure consists of 15 InGaAs QD layers and the waveguide layout comprises two differently tapered sub-sections and a straight input section.