M2 Factors Research Articles

Compact Partially End-Pumped Innoslab Laser Based on Micro-Cylindrical Lens Array Homogenizer

We demonstrate a compact, partially end-pumping Innoslab laser based on a micro-cylindrical lens array homogenizer. A dimension of 12 × 0.4 mm2 flat-top pumping line with a Gaussian intensity distribution across the line was simulated by the ray tracing technique. The rate equations considering the asymmetric transverse spatial distributions are theoretically developed. The simulation results are in good agreement with the experimental results. Preliminary data shows that for a pump power of 260 W, a maximum pulse energy of 15.7 mJ was obtained with a pulse width of 8.5 ns at a repetition frequency of 1 kHz. The beam quality M2 factors in the unstable and stable directions were 1.732 and 1.485, respectively. The technology has been successfully applied to temperature and humidity profiling lidar and ozone lidar and has been productized, yielding direct economic value.

High power widely tunable frequency-doubled 490 nm blue semiconductor disk laser

This paper presents a high power widely tunable frequency-doubled semiconductor disk laser emitting at 490 nm wavelength. The laser utilizes a specially designed gain chip with widened gain spectrum at the center wavelength of 980 nm, along with an anti-resonant microcavity, to extend the tuning range of the wavelength. A type-I phase-matched 5 mm length LBO crystal is used as the nonlinear crystal, and a fused quartz birefringent filter (BRF) is introduced to polarize the fundamental emission and narrow the linewidth of the laser. When the thickness of the used BRF is 1 mm, 50.7 nm tuning range of the 980 nm infrared laser is performed. A maximum output power of 5.36 W of the frequency-doubled 490 nm blue laser is achieved, and the optical-to-optical conversion efficiency from absorbed pump power to the blue light is about 15.3%. Meanwhile, a record tuning range of 21.5 nm of the blue laser is realized. The measured M2 factors of the blue laser are 1.00 in the x-direction and 1.04 in the y-direction, respectively.

Kilowatt-Level High-Efficiency Narrow-Linewidth All-Fiber Tm3+-Doped Laser

In this study, a kilowatt-level high-efficiency narrow-linewidth all-fiber Tm3+-doped continuous-wave laser operating at 1.95 μm is demonstrated. Benefitting from an advanced boost design of a two-stage main amplifier, it not only effectively manages heat dissipation resulting from the high pump-induced quantum defect but also realizes the controlled extraction of optical gain and improves the optical conversion efficiency. Finally, this laser system has realized an output power of 1018 W, a linewidth of 3.8 GHz, and a slope efficiency of 60.0% simultaneously. Moreover, a high optical signal-to-noise ratio of over 45 dB and excellent beam quality of M2 factors 1.19 are obtained. To the best of our knowledge, this represents the narrowest linewidth and highest slope efficiency achieved in a kilowatt-level Tm³⁺-doped fiber laser. Such a high-performance laser is ideally suited for mid-infrared generation and remote sensing applications.

High brightness terahertz quantum cascade laser with near-diffraction-limited Gaussian beam

High-power terahertz (THz) quantum cascade laser, as an emerging THz solid-state radiation source, is attracting attention for numerous applications including medicine, sensing, and communication. However, due to the sub-wavelength confinement of the waveguide structure, direct beam brightness upscaling with device area remains elusive due to several mode competition and external optical lens is normally used to enhance the THz beam brightness. Here, we propose a metallic THz photonic crystal resonator with a phase-engineered design for single mode surface emission over a broad area. The quantum cascade surface-emitting laser is capable of delivering an output peak power over 185 mW with a narrow beam divergence of 4.4° × 4.4° at 3.88 THz. A high beam brightness of 1.6 × 107 W sr−1m−2 with near-diffraction-limited M2 factors of 1.4 in both vertical and lateral directions is achieved from a large device area of 1.6 × 1.6 mm2 without using any optical lenses. The adjustable phase shift between the lattices enables a stable and high-intensity surface emission over a broad device area, which makes it an ideal light extractor for large-scale THz emitters. Our research paves the way to high brightness solid-state THz lasers and facilitates new applications in standoff THz imaging, detection, and diagnosis.

Comparison on performances of continuous and pulsed operation in anti-misalignment laser of Er:YAG and Er:LuAG crystals

The thermal focal lengths, absorption efficiencies, and laser performances of Er:YAG and Er:LuAG crystals are systematically demonstrated within an anti-misalignment double corner-cube-prisms resonator. The maximum continuous-wave output power of 5.12 W at 1645.39 nm and 6.43 W at 1650.33 nm are obtained, with slope efficiencies of 16.29 % and 36.78 %. In pulsed operation, Er:YAG yielded a maximum pulse energy of 5.1 mJ, and Er:LuAG delivered 4.7 mJ, both at the pulse repetition rate of 200 Hz. The beam qualities, represented by M2 factors, are measured at 1.52 for Er:YAG and 1.44 for Er:LuAG.

Coherent beam combining of femtosecond third-harmonic generators: towards high-power, high-beam-quality UV light generation.

Coherent beam combining (CBC) of two femtosecond third-harmonic (TH) generators is proposed and demonstrated. By applying phase modulation to one of the fundamental laser pulses, the feedback loop effectively eliminates both phase and pointing errors between the two TH femtosecond laser beams. The system delivers 345-nm femtosecond laser pulses with 22-W average power at 1-MHz repetition rate. The average combining efficiency is 91.5% over approximately 1 h of testing. The beam quality of the combined ultraviolet (UV) laser beam is near-diffraction-limited with M2 factors of M X2=1.36, M Y2=1.24, which are similar to those of the individual channels. This scheme exhibits promising potential for increasing high-beam-quality UV laser power.

M2 macrophage-derived soluble factors enhance neuronal density in the frontal cortex of depression-like mice

IntroductionChronic inflammation in depression is associated with decreased levels of neurotrpohic factors and suppressed neurogenesis. We have previously shown that intranasal therapy with soluble factors from M2 macrophages polarized by interaction with apoptotic cells in serum deprivation conditions (M2(LS); LS - low serum) and characterized by anti-inflammatory and pro-regenerative activity leads to the correction of the behavioral pattern in mice with a depression-like state.ObjectivesThe present study focuses on the effect of M2(LS) macrophages on neuronal density in the frontal cortex and hippocampus of depression-like mice.MethodsDepressive-like state was formed in passive male mice (CBAxC57Bl/6)F1) as a result of repeated experience of defeat in agonistic interactions with aggressive partner during 20 days (the sensory contact model). Depression-like mice were then treated intranasally with M2(LS) macrophages conditioned medium for 7 days. After that, the number of mature neurons in the frontal cortex and hippocampus was assessed using Nissl staining.ResultsThe neuronal density in the pyramidal layer of the frontal cortex was significantly lower in depression-like mice than that in the intact control group of mice (p=0,047). At the same time, the number of neurons in the experimental group of mice that received soluble M2(LS) factors, was higher than that in depressive-like untreated control mice (p=0,003) and was comparable to that in the intact group of mice. At the same time the neuronal density in the CA1 and CA3 hippocampal areas did not change in depression-like mice following intranasal treatment with conditioned medium of M2(LS) macrophages.ConclusionsThe data obtained may indicate the neuroprotective effect of M2(LS) macrophages in the stress-induced depression model, which is realized through soluble factors and manifests itself in an increase of the pyramidal neurons density in the frontal cortex.Disclosure of InterestNone Declared

Watt-level output power and near-diffraction-limit beam quality mid-infrared Ho:GdVO4 self-Raman laser at 2.5 µm.

We demonstrate an efficient active Q-switched Ho:GdVO4 self-Raman laser at 2500 nm for the first time, to our knowledge. Using Ho:GdVO4 crystal as the gain medium for both the 2048nm fundamental laser and the 2500 nm Raman laser, the output performances of a new mid-infrared self-Raman laser were investigated. The maximum average output power of 1.45 W was achieved at an incident pump power of 22.5 W, with a slope efficiency of 25.8%, for an output transmittance of 30% and a pulse repetition frequency of 15 kHz. The maximum single pulse energy of 96.7 µJ with a pulse width of 11.35 ns was obtained, corresponding to the peak power of 8.5 kW. The beam quality was near diffraction limited with the M2 factors of 1.15 and 1.06 along the x and y directions. Moreover, adopting the two-end output way of the fundamental laser and the Raman laser, the Raman gain coefficient of Ho:GdVO4 crystal was estimated to be 1.14 cm/GW at 2048nm. This work shows that Ho:GdVO4 is an excellent self-Raman laser crystal for the generation of high power Raman laser at 2.5 µm.

Mid-infrared idler-resonant optical vortex parametric oscillator based on MgO:PPLN

We present a high beam quality, mid-infrared, wavelength tunable, idler-resonant optical vortex parametric oscillator based on a single-grating MgO-doped periodically poled lithium niobate (MgO:PPLN) crystal. The compact, plane-concave cavity used in this work enabled transfer of the orbital angular momentum (OAM) of the pump field to the idler field, to deliver high beam quality, mid-infrared vortex beam emission with measured M2 factors of 2.2 in both orthogonal directions. The wavelengths of the signal (which had a TEM00/Gaussian-like spatial profile) and the idler vortex outputs could be tuned across the ranges 1.505–1.566 µm and 3.318–3.628 µm, respectively, by changing the MgO:PPLN crystal temperature in the range 25 to 200℃. We also investigate the mechanism of OAM transfer within the idler-resonant MgO:PPLN optical parametric oscillator (OPO) by tuning the cavity length. Here, we find that the OAM of the pump beam can be selectively transferred to the signal field by simply extending the cavity length. The maximum measured signal and idler vortex output energies were 3.3 mJ and 1.1 mJ, respectively, and were achieved using both compact and extended cavities at a pump energy of 21 mJ.

M2pep-Modified Cyclodextrin-siRNA Nanoparticles Modulate the Immunosuppressive Tumor Microenvironment for Prostate Cancer Therapy.

Prostate cancer (PCa) is the most prevalent cause of cancer deaths in men. Conventional strategies, such as surgery, radiation, or chemotherapy, face challenges including poor prognosis and resistance. Therefore, the development of new improved strategies is vital to enhance patient outcomes. Recently, immunotherapy has shown potential in the treatment of a range of cancers, including PCa. Tumor-associated macrophages (TAMs) play an important role in the tumor microenvironment (TME) and reprogramming of TAMs is associated with remodeling the TME. The colony-stimulating factor-1/colony stimulating factor-1 receptor (CSF-1/CSF-1R) signaling pathway is closely related to the polarization of TAMs. The downregulation of CSF-1R, using small interfering RNA (siRNA), has been shown to achieve the reprogramming of TAMs, from the immunosuppressive M2 phenotype to the immunostimulatory M1 one. To maximize specific cellular delivery an M2 macrophage-targeting peptide, M2pep, was formulated with an amphiphilic cationic β-Cyclodextrin (CD) incorporating CSF-1R siRNA. The resulting nanoparticles (NPs) increased M2 macrophage targeting both in vitro and in vivo, promoting the release of M1 factors and simultaneously downregulating the levels of M2 factors through TAM reprogramming. The subsequent remodeling of the TME resulted in a reduction in tumor growth in a subcutaneous PCa mouse model mainly mediated through the recruitment of cytotoxic T cells. In summary, this M2pep-targeted CD-based delivery system demonstrated significant antitumor efficacy, thus presenting an alternative immunotherapeutic strategy for PCa treatment.

Investigation of gain-filtering Yb-doped fibers with different gain-dopant doping ratios for high power amplifier

We presented an investigation on gain-filtering Yb-doped fiber for the mitigation of transverse mode instability (TMI). The gain-filtering Yb-doped fibers were fabricated by modified chemical vapor deposition (MCVD) combined with solution doping technique. Four gain-dopant diameter ratio fibers, entailing 100% doping, ∼73% doping, Gaussian doping, and ∼57% doping, presented similar parameters with the core/inner cladding diameter of ∼30/400 μm and core numerical aperture (NA) of ∼0.061. The laser performances of four fibers were demonstrated by a bidirectional pumping all-fiber amplifier. The TMI thresholds of 100%-doped, ∼73%-doped, Gaussian-doped, and ∼57%-doped fibers, were measured to be ∼1753 W, ∼3089 W, ∼3048 W, and over 3301 W, corresponding to the M2 factors of ∼1.52, ∼1.40, ∼1.45, and ∼1.32, respectively. The experimental results indicated that by reasonably tailoring the gain-dopant doping diameter, better gain-filtering effect was manifested, exactly as higher TMI threshold and more superior beam quality. This contribution could provide an effective approach for obtaining high-brightness Yb-doped fiber amplifiers based on gain-filtering effect.

500 Hz single-frequency, pulsed Er:YAG laser in the double corner cube retroreflector resonator

We have demonstrated an injection-seeded, single-frequency Q-switched Er:YAG laser at the pulse repetition frequency (PRF) of 500 Hz with the ‘double piezoelectric transducers (PZTs) structure’, in a double corner cube retroreflector (DCCR) resonator. With the ‘ramp-hold-fire’ method, the maximum 1.34 mJ pulse energy with a pulse width of 482 ns has been achieved. With the heterodyne beating technique, the full width at the half maximum (FWHM) of the laser spectrum is 1.12 MHz. And the M2 factors of the 500 Hz, single-frequency pulsed laser are 1.2, 1.24 along the horizontal and vertical directions.

A high-energy Ho: YLF MOPA system pumped by Tm: YAP lasers

This paper introduces a high-energy Q-switched Ho: YLF master oscillator power amplifier (MOPA) system pumped using linearly polarized Tm: YAP lasers. In this system, the pulse repetition frequency was 100 Hz, and an 84.7 mJ Ho laser was generated with a total pump power of 102.3 W, corresponding to a total optical conversion efficiency of 8.3%. The oscillator yielded a maximum output energy of 20.0 mJ and pulse width of 19.0 ns, corresponding to a peak power of 1.05 MW. Moreover, the amplifier delivered a maximum output energy of 84.7 mJ and pulse width of 18.0 ns, corresponding to a peak power of 4.70 MW. In addition, the system exhibited an excellent beam quality in both directions, with the M2 factors better than 1.1 and 1.3 at the oscillator and amplifier, respectively.

Structure, spectroscopy and laser performance of an Er:YGGAG crystal.

In this work, we report on investigations of structure, spectroscopic properties and laser performances of, what we believe to be, a novel Er:YGGAG laser crystal. High crystalline quality is proved by an FWHW of XRC of 0.019°. Thermal conductivity of a 30 at.% Er:YGGAG crystal is determined as 4.98 W/(m·K). The refractive index is measured in the range of 400 to 1000 nm and fitting with Sellmeier equation is done. A broad fluorescence emission band is located at 2786∼2819 nm, suggesting that this crystal is favorable to realize tunable and ultrafast laser. Under the pump at 969 nm with a fiber-coupled diode laser, at 400 Hz repetition rate and 600 µs pulse duration, the 30 at.% Er:YGGAG delivered maximum average power of 506 mW with overall optical-to-optical efficiency of 12.4% and slope efficiency of 16.9%. The laser beam quality was characterized by M2 factors of 1.53 and 1.39 in horizontal and vertical directions, respectively.

Performance Studies of High-Power Optical Parametric Oscillators Pumped by a Pulsed Fiber Laser

High-power optical parametric oscillators (OPOs), as mature radiation sources in mid-infrared (MIR), degenerate gradually with wavelength increase, mainly above 3700 nm. Using a periodically poled magnesium-oxide-doped lithium niobate (MgO:PPLN) as the nonlinear crystal, we build a high-power signal-resonant OPO pumped by ytterbium-doped fiber laser (YDFL). To improve the OPO’s output power at ~3.8 μm, the parameters, such as the pump beam’s waist diameter and location, the curvature radius of the output coupler and the length of MgO:PPLN, are discussed in detail. When pump power is 79 ± 4 W with a repetition rate of 200 kHz, the OPO provides up to 8 ± 0.4 W average power in beam quality with M2 factors of ~1.84 and ~1.69 in the two axes. Under the highest output power, the center wavelength of the idler beam is 3768.4 nm with a full-width at half-maximum (FWHM) bandwidth of ~18.6 nm. When the output power reaches ~6.3 W, its power stability is 1.6% root mean square (RMS) over 7 h. Further analysis of the factors affecting OPO’s performance and simple structure are critically essential for compact OPO prototypes with a capacity of high output power.

Effect of soluble factors of macrophages polarized by efferocytosis on neuronal density in the frontal cortex and hippocampus of mice in a model of stress-induced depression

Recently, there has been a steady increase in depressive disorders, which occupy an important place in the structure of the causes of disability. In the pathogenesis of depression, an important role is played by neuroinflammation, which is associated with impaired adult neurogenesis. Notably, neuroinflammation is partially reversible, and the leading role in the initiation and regulation of neuroregeneration is given to macrophages. Opposite states of macrophage activation are classically activated M1 and alternatively activated M2 macrophages, characterized, respectively, by pro- and anti-inflammatory activity. A balance shift towards M2 macrophages has been considered as a new therapeutic strategy of psycho-neurological disorders. One of the inducers of the M2 phenotype is the efferocytosis. We have previously developed an original protocol for the generation of human macrophages under conditions of deficiency of growth / serum factors, in which M2 phenotype is formed through efferocytosis. Macrophages (M2(LS), LS – Low Serum) obtained according to this protocol express M2-associated markers, and are characterized by high production of growth and pro- angiogenic factors (IGF-1, VEGF, BDNF, EGF, FGF-basic, etc.), which can suppress inflammation and stimulate neuroregeneration / neuroplasticity. In the model of stress-induced depression, the antidepressant effect of soluble factors of M2(LS) macrophages was shown, accompanied by a decrease in the level of pro- inflammatory cytokines in certain brain structures. However, the effect of M2(LS) factors on neurogenesis remained unexplored. In the present work, which is a continuation of the aforementioned study, we analyzed the effect of intranasal administration of M2(LS) soluble factors on neuronal density in different brain areas – the frontal cortex and hippocampus – of depression-like mice. The results obtained showed that neuronal density in the frontal cortex, CA1 and CA3 zones of the hippocampus, was significantly higher in mice with intranasal administration of M2(LS) conditioned medium than in depression-like mice, and reached the level of neuronal density in intact animals. These results may indicate the neuroregenerative activity of M2(LS) macrophages in the model of stress-induced depression, which is mediated through soluble factors and manifests itself in an increase in the density of neurons in the brain.

High-energy femtosecond pulse generation from a hybrid mode-locked large-mode-area Er:ZBLAN fiber laser.

We report a hybrid mode-locked fiber laser at 2.8 µm based on a large-mode-area Er:ZBLAN fiber. Reliable self-starting mode-locking is achieved via the combination of nonlinear polarization rotation and a semiconductor saturable absorber. Stable mode-locked pulses with a pulse energy of 9.4 nJ and a pulse duration of 325 fs are generated. To the best of our knowledge, this is the highest pulse energy directly generated from a femtosecond mode-locked fluoride fiber laser (MLFFL) to date. The measured M2 factors are below 1.13, indicating a nearly diffraction-limited beam quality. Demonstration of this laser provides a feasible scheme for the pulse energy scaling of mid-infrared MLFFLs. Moreover, a peculiar multi-soliton mode-locking state is also observed, in which the time interval between the solitons varies irregularly from tens of picoseconds to several nanoseconds.

1.8 W, high efficiency, pump-enhanced, narrow linewidth optical parametric oscillator at 3.8 µm.

A high efficiency, continuous-wave, narrow linewidth, pump-enhanced optical parametric oscillator (OPO) at 3.8 µm was demonstrated, which was pumped by a 1064 nm fiber laser with a linewidth of 18 kHz. The low frequency modulation locking technique was employed to stabilize the output power. The wavelengths of signal and idler were 1475.5 nm and 3819.9 nm at 25 °C, respectively. The pump-enhanced structure was applied, leading to a maximum quantum efficiency of over 60% with pump power of 3 W. The maximum output power of idler light is 1.8 W with a linewidth of 363 kHz. The excellent tuning performance of the OPO was also demonstrated. In order to avoid mode-splitting and decrease of pump enhancing factor due to feedback light in the cavity, the crystal was placed obliquely to the pump beam and the maximum output power was increased by 19%. At the maximum output power of idler light, the M2 factors in the x and y directions were 1.30 and 1.33, respectively.

High Brightness Diode Laser Based on V-Shaped External Cavity and Beam-Waist Splitting Polarization Combining

A beam combining method to improve the brightness of diode lasers is proposed based on a V-shaped external cavity spectral beam and beam-waist splitting polarization combination. This design has the outstanding advantages of improving the beam quality, brightness, and versatility of the diode laser. Specifically, an output power over 16W with M2 factors of 1.79 × 3.92 (Beam Parameter Product BPP = 0.55 × 1.22 mm mrad) at 40 A in the fast and slow axis is demonstrated for a commercial standard cm-bar. Furthermore, the slow axis M2 of the combined laser is improved by 56% compared with that of a single emitter. Additionally, the brightness of 262 MW·cm−2·sr−1, 136% higher than that of spectral beam combining without using beam-waist splitting polarization, was realized.

Improvement of 2.8 μm laser performance on LD side-pumped LuYSGG/Er:LuYSGG/LuYSGG bonding crystal

We demonstrate the laser performance of 970 nm LD side-pumped LuYSGG/Er:LuYSGG/LuYSGG bonding crystal in a frequency range of 50–800 Hz. The thermal distribution simulation implies that the bonded Er:LuYSGG crystal possesses a higher cooling efficiency compared with the un-bonded one. The maximum average power of 20.76 W is realized at a frequency of 150 Hz and a pulse width of 200 μs, corresponding to a slope efficiency of 23.94 % and optical-to-optical conversion efficiency of 19.22 %. A single laser wavelength of 2797.5 nm is observed. The M2 factors of the bonding rod are 6.80/6.74, indicating a relatively high beam quality. Therefore, the LuYSGG/Er:LuYSGG/LuYSGG bonding crystal exhibits an improvement of laser performance operated at 2.8 μm due to excellent heat dissipation ability, which is a promising gain element and can be applied to the harsh radiation environment.