Μm Laser Research Articles

Uncooled Broadband Photodetection via Light Trapping in Conformal PtTe2-Silicon Nanopillar Heterostructures.

Dirac semimetals have demonstrated significant attraction in the field of optoelectronics due to their unique bandgap structure and high carrier mobility. Combining them with classical semiconductor materials to form heterojunctions enables broadband optoelectronic conversion at room temperature. However, the low light absorption of layered Dirac semimetals substantially limits the device's responsivity in the infrared band. Herein, a three-dimensional (3D) heterostructure, composed of silicon nanopillars (SiNPs) and a conformal PtTe2 film, is proposed and demonstrated to enhance the photoresponsivity for uncooled broadband detection. The light trapping effect in the 3D heterostructure efficiently promotes the interaction between light and PtTe2, while also enhancing the light absorption efficiency of silicon, which enables the enhancement of the device responsivity across a broadband spectrum. Experimentally, the PtTe2-SiNPs heterojunction device demonstrates excellent photoelectric conversion behavior across the visible, near-infrared, and long-wave infrared (LWIR) bands, with its responsivity demonstrating an order-of-magnitude improvement compared to the counterparts with planar silicon heterojunctions. Under 11 μm laser irradiation, the noise equivalent power (NEP) can reach 1.76 nW·Hz-1/2 (@1 kHz). These findings offer a strategic approach to the design and fabrication of high-performance broadband photodetectors based on Dirac semimetals.

Wavelength extension beyond 3 µm in a Ho3+/Pr3+ co-doped AlF3-based fiber laser.

In this Letter, we report continuous-wave (CW) lasers with wavelengths beyond 3 µm in homemade Ho3+/Pr3+ co-doped AlF3-based glass fibers. The laser cavity was established through the integration of a dichroic mirror (DM, HR@3-3.1 µm) positioned at the pump end and a partial reflectivity (PR) fiber Bragg grating (FBG) situated at the laser emission end. The FBGs in AlF3-based glass fibers were fabricated by a fs laser direct-writing method, and the resonant wavelengths were 3.009, 3.036, and 3.064 µm, respectively. Under the pump of 1.15 µm laser, a maximum unsaturated output power of 1.014 W was obtained at 3.009 µm with an overall laser efficiency of 11.8% and FWHM bandwidth of 0.88 nm. Furthermore, in order to enhance the optical-thermal stability, the FBG was heat-treated at 200°C for 30 min, and a higher output power of 1081 mW (348 mW without heat treatment) at 3.036 µm was achieved. To the best of our knowledge, this is the first demonstration of 3-3.1 µm lasers by using FBGs in Ho3+/Pr3+ co-doped AlF3-based fibers.

Terawatt-class femtosecond long-wave infrared laser

We utilized a nonlinear post-compression technique to generate 675-fs, 9.2-μm CO2 laser pulses with a peak power of 1.6 TW. This achievement represents the highest peak power ever attained in the femtosecond pulse format within the long-wave infrared (LWIR) spectral range. The successful implementation of this post-compression technique opens avenues for the development of few-cycle, multi-terawatt 9–10 μm lasers, crucial for applications currently relying on near-infrared solid-state lasers, and which stand to benefit from the scaling of laser wavelengths into the long-wave infrared region.

Design and fabrication of a tellurite hollow-core anti-resonant fiber for mid-infrared applications

The hollow core anti-resonant fibers (HC-ARFs) based on soft glass are in high demand for 3-6 µm laser delivery. A HC-ARF based on tellurite glass with 6 touching capillaries as cladding was designed and fabricated for the first time, to the best of our knowledge. A relatively low loss of 3.75 dB/m at 4.45 µm was realized in it. The effects of capillary number, core diameter, wall thickness of capillary, and material absorption loss on the loss of the HC-ARF were analyzed by the numerically simulation. The output beam quality was measured and the influence of bending on the fiber loss was discussed. The results of numerical simulation suggested that the theoretical loss of the prepared fiber can be reduced to 0.1 dB/m, indicating that tellurite HC-ARFs have great potential for mid-infrared laser applications.

Murine Models of Laser Interstitial Thermal Therapy for Immuno-Oncology

INTRODUCTION: Cytoreductive surgery is a cornerstone of management for intracranial tumors. However, such treatment may remove an important source of neoantigen. In the case of laser interstital thermal therapy (LITT), thermally-ablated tumor remans in situ, allowing for a potential anti-tumor immune response. METHODS: Brain tumor cell lines (CT-2A) were stereotactically implanted into C57BL/6 mice. A 1064 nm Nd:YAG laser (Neuroblate, Monteris Medical) was used to ablate normal brain and tumor tissue. RESULTS: To establish anatomical boundaries for our ablation, we characterized our CT-2A model on T2 MRI, selecting 10 days post-implantation for LITT based on lesion size. We simultaneously implanted a 400 μm laser fiber and thermocouple probe into the center and edge of the target volume, respectively, for simultaneous ablation and temperature monitoring. To characterize the laser's effects, we first performed a dose titration of laser power/time in normal mouse brains, finding that doses above 2 W for 30 s produced cavitary lesions with charring that resulted in death at 24 h post-LITT. We therefore selected 1 W for 60 s as a safe laser power dose in our tumor model. Ablations at this setting rapidly heated the lesion edge to a peak temperature of mean 43.79 ± 2.993 °C, sparing the surrounding brain. MRI imaging at 1, 3, and 7 days post-LITT revealed an expansile T2 hyperintense lesion, with hemmorhage and necrosis on H&E. LITT increased survival to 28 from 25.5 days (vs sham, p = 0.0172). CONCLUSIONS: Using a clinical laser system, we were able to model the essential clinicopathological effects of LITT in mice: a cytoreductive survival benefit; lesion expansion on MRI; and focal necrosis with hemorrhagic vasculature on H&E. This model allows for detailed immunological studies of LITT and use with existing brain metastasis cell lines.

Fabrication of double-cladding fluoroindate glass fibers and watt-level 2.7 μm laser application

We report a double-cladding fluoroindate fiber with three layers of step refractive index glass. The gain double-cladding fluoroindate fiber is fabricated by the traditional rob-in-tube method. It possesses a tunable refractive index from 1.46 to 1.51 via modification of glass components. The good thermal–mechanical performance of fluoroindate glass protects fiber against thermal damage. The luminescence characteristics and radiation parameters are studied, and the results indicate enhanced emission with the higher Er3+ doping concentration. The maximum output power and the slope efficiency of heavily erbium-doped fiber laser are about 1.2 W and 16.3 %, respectively. The numerical modeling of a heavily-erbium-doped fluoroindate fiber laser is also carried out and compared with our experimental results. The low phonon energy and high laser damage threshold of fluoroindate glass allow for higher output power and efficiency of fiber lasers. In brief, this is the first study on watt-level 2.7 μm fiber laser in all-solid double-cladding fluoroindate fibers to our knowledge.

InAs quantum dots with a narrow photoluminescence linewidth for a lower threshold current density in 1.55 µm lasers

Uniform quantum dots (QDs) with a narrowed linewidth of photoluminescence (PL) are crucial for developing high-performance QD lasers. This study focuses on optimizing the growth conditions of InAs QDs on (001) InP substrates using metal-organic chemical vapor deposition (MOCVD), targeting applications in 1.55 µm QD lasers. By fine-tuning growth parameters such as the V/III ratio, deposition thickness, and growth temperature, we attained a QD density of 4.13 × 1010 cm−2. Further, a narrowed PL full width at half maximum (FWHM) of 40.1 meV was achieved in a five-stack InAs QD layer. This was accomplished using the double-cap technique, which reduced the height dispersion of QDs and shifted the emission wavelength to 1577 nm. Broad-area lasers incorporating a five-stack optimized InAs/InAlGaAs structure demonstrated a low threshold current density of 80 A/cm2 per QD layer, and a saturation power of 163 mW in continuous-wave (CW) mode at room temperature.

All-solid-state ultrafast 2µm laser with 1.83 W output power.

In this paper, a high-power all-solid-state ultrafast 2µm mode-locked laser is investigated. The particularity of this laser is the simultaneous utilization of two Tm:YAP crystals in the same resonant cavity, independently pumped by two laser diodes. Using a 20% output coupler, pulses with output power as high as 1.83W are achieved at a wavelength of 1938nm with a pulse duration of 1.97ps and a pulse repetition frequency of 100MHz. To our knowledge, this mode-locked laser achieves the highest output power of any mode-locked Tm:YAP ultrafast laser reported to date. In addition, this paper provides a new approach to solve the problem of low output power due to multi-mode low-brightness laser diode pumping.

Investigation of pulse burst characteristics in an LD end-pumped Er:Yb:Glass/Co:MALO microchip 1.5 μm laser

Burst mode lasers, characterized by a sequence of high-intensity pulses, are integral to applications such as the examination of turbulent flows and optical metrology. This study investigates a 1.5 μm passively Q-switched pulse burst microchip laser, end-pumped by a 940 nm laser diode. Utilizing Er:Yb:glass as the gain medium and Co:MALO for passive Q-switching, delivering a pulse width of 5.5 ms and a repetition rate of 10 Hz. When the initial transmittance of the saturable absorber was 93 % and the maximum absorbed pump energy reached 85 mJ, we successfully generated up to 12, 8, and 4 pulses within a burst at 1.5 μm. These results corresponded to cavity lengths of 12 mm, 13 mm, and 14 mm, respectively. By using a saturable absorber with an initial transmittance of 90.5 %, a higher single pulse energy and a narrower pulse width were realized. The narrowest pulse width was reduced to 6.2 ns, with a corresponding single pulse energy of 272 μJ. The peak power in the Er:Yb:glass/Co:MALO pulse burst laser reached an estimated 43.9 kW.This research provides valuable experimental and theoretical insights for the development of human eye-safe lasers with adjustable pulse sequences.

Demonstration of a 1 TW peak power, joule-level ultrashort Tm:YLF laser

We report on the demonstration of a diode-pumped, Tm:YLF-based, chirped pulse amplification laser system operating at λ ≈ 1.9 µm that produces amplified pulse energies exceeding 1.5 J using a single 8-pass power amplifier. The amplified pulses are subsequently compressed to sub-300 fs durations by a diffraction grating pair, producing record >1 TW peak power pulses. To the best of our knowledge, this is the highest peak power demonstrated for any solid-state, near-2 µm laser architecture and illustrates the potential of Tm:YLF for the next generation of high-power, diode-pumped ultrashort lasers.

Comparison of three nanoparticle deposition techniques potentially applicable to elemental mapping by nanoparticle-enhanced laser-induced breakdown spectroscopy

In this study, we compared the applicability of three nanoparticle deposition techniques (spray coating, spark discharge nanoparticle generation, magnetron sputtering) towards elemental mapping by nanoparticle-enhanced laser-induced breakdown spectroscopy (NE-LIBS). It was found that sputtering followed by a thermal treatment at 550 °C can provide a homogenous, practical and controllable way of NE-LIBS sample preparation with gold nanoparticles. The laser ablation properties of the created NP layer was also studied in detail and it was established that a 200 μm laser spot size is good compromise between the NE-LIBS signal enhancement and the spatial resolution required for mapping. A signal enhancement of about a factor of 10 with good repeatability (ca. 5 %RSD) in a line scanning demonstration was achieved on glass for Si detection. For samples that are fairly temperature and vacuum stable, this approach allows the signal enhancement to be used in mapping applications.

Investigation of Light-Scattering Properties of Non-Spherical Sea Salt Aerosol Particles at Varying Levels of Relative Humidity

In the marine environment, sea salt aerosol particles transition from cubic or rectangular shapes when dry to various non-spherical shapes like ellipsoids and cylinders under different humidities. The complex humidity conditions and particle morphologies pose challenges to simulating the optical scattering properties of non-spherical sea salt aerosols. This study, addressing real environmental scenarios, employs the randomly oriented T-matrix computational method to calculate the optical scattering and polarization characteristics of sea salt aerosols at a wavelength of 1.06 μm under three relative humidity conditions (50%, 80%, and 95%) and three particle morphologies (spheroid, circular cylinder, and Chebyshev particle shapes). The results show the following: (1) In terms of optical scattering properties, the greater the non-sphericity of particles under the same humidity conditions, the larger the deviation between non-spherical and spherical models. For spheroid and circular cylinder sea salt aerosols, the error in the extinction efficiency factor mainly lies within 10–30%, reaching up to 120%; the error in the asymmetry factor is primarily between 3 and 25%, with a maximum of 75%, and the error in the forward-scattering phase function is mainly within 10–60%, reaching up to 180%. Chebyshev particle-shaped sea salt aerosols exhibit smaller deviations in optical scattering properties compared to equivalent spherical models, generally within the 5–25% range. Under different humidity conditions, the scattering characteristic parameters of sea salt aerosol particles for various non-spherical models show a positive correlation with relative humidity. When relative humidity is below 70%, the optical scattering properties of differently shaped sea salt aerosols are less affected by relative humidity. Above 70% relative humidity, the optical scattering properties of sea salt aerosols of different shapes become more sensitive to changes in relative humidity. (2) Regarding polarization properties, the greater the humidity, the more significant the impact on polarization properties, and as humidity increases, sea salt aerosols with higher non-sphericity exhibit more complex changes in polarization characteristics. The differences in shapes of non-spherical models mainly affect the numerical values of polarization properties. Under the same humidity conditions, spheroid polarization characteristics are significantly different from other models. In terms of depolarization ratio for aerosols, circular cylinder sea salt aerosols show the highest depolarization ratio at various relative humidities, followed by spheroid, with Chebyshev-shaped having the least. The effect of relative humidity on the depolarization ratio varies with the scattering angle. The higher the relative humidity, the more complex the variation in the depolarization ratio with scattering angle, with more pronounced oscillations in the curve, and the less non-spherical the shape, the more intense the oscillations in the depolarization ratio curve due to humidity. In conclusion, this study calculated the optical scattering and polarization properties of sea salt aerosol particles under different relative humidities and shapes, which is of significant importance for applications like 1.06 μm laser engineering and atmospheric radiation transmission in actual marine scenarios.

Selective 1.3 μm Laser Emission via Coupled Microlaser for Laser Resonance Tuning

Selective 1.3 μm Laser Emission via Coupled Microlaser for Laser Resonance Tuning

Polarized spectral characteristics and 1.5–1.6 μm laser operation of Er:Yb:CaSrAl2SiO7 crystal

An Er:Yb:CaSrAl2SiO7 single crystal was grown by the Czochralski method, and its polarized spectral properties were investigated at room temperature. The peak absorption cross-sections of the crystal at 978 nm are 3.30 × 10−20 and 1.42 × 10−20 cm2 for σ and π polarizations, respectively. The peak emission cross-sections at 1536 nm are 0.87 × 10−20 and 0.95 × 10−20 cm2 for σ and π polarizations, respectively. The fluorescence lifetime of the 4I13/2 multiplet of Er3+ is 8.66 ms, and energy transfer efficiency from Yb3+ to Er3+ in the crystal is 70%. Pumped by a 975 nm diode laser, a continuous-wave laser with a slope efficiency of 5.5% and a maximum output power of 70 mW was achieved in the Er:Yb:CaSrAl2SiO7 crystal.

Spectroscopic and 1.5–1.6 μm laser properties of Er:Yb:GdSr3(PO4)3 crystal

An Er:Yb:GdSr3(PO4)3 crystal was grown by the Czochralski method, and its spectroscopic properties were investigated at room temperature. The peak absorption cross section is 1.12 × 10−20 cm2 at 975 nm and the full width at half maximum of the absorption band is 5.8 nm. The peak emission cross section is 0.74 × 10−20 cm2 at 1535 nm and the full width at half maximum of the fluorescence band is 41 nm. Fluorescence lifetime of the 4I13/2 multiplet of Er3+ and Yb3+→Er3+ energy transfer efficiency in the crystal are 7.97 ms and 91.8 %, respectively. End-pumped by a 975 nm diode laser, a 1563 nm continuous-wave laser with a maximum output power of 60 mW and a slope efficiency of 16.1 % was realized in an Er:Yb:GdSr3(PO4)3 crystal at an absorbed pump power of 413 mW. Using a SiO2 birefringent filter as a wavelength tuning element, a continuously tunable 1.5–1.6 μm laser with a range of 45 nm and a maximum output power of 30 mW at 1541 nm was obtained at the same pump power.

Thirty versus 60-Watt thulium laser enucleation of prostate: Toward the development of low-power anatomical enucleation of the prostate.

We aimed to study whether using 30 W versus 60 W thulium enucleation of the prostate (ThuLEP) would affect postoperative outcomes in patients with benign prostatic hyperplasia (BPH). We prospectively identified male patients with moderate or severe lower urinary tract symptoms due to BPH. We randomized patients into 30 W (Group 1) or 60 W (Group 2) thulium yag laser with a 550 μm laser fiber and a 26 Fr continuous flow resectoscope. We collected data related to prostate size, enucleation time, morcellation time, laser time, perioperative complications, and 1-year functional outcomes. A total of 120 patients were included, with a mean age of 67 years and a mean prostate size of 105 g. The preoperative characteristics were similar across both groups. The mean operative time was shorter in the 60 W group, 74 ± 27 vs. 91 ± 33 min in the 30 W group (P = 0.001), and the mean laser time was 55 ± 20 in 60 W versus 71 ± 25 in 30 W (P = 0.0001). The mean hospital stay was 1 day in both groups and at 1-year follow-up; there was a similar improvement in mean Qmax and International Prostate Symptom Score symptom scores. Both 30 and 60 W ThuLEP provided a safe and comparable outcome with a relatively shorter operative time for the 60 W groups. Perhaps using a 30-W setting would be beneficial in the early learning curve or cases with more bleeding capsular perforators; besides, the financial benefit of manufacturing low-cost low-power devices that may help in the widespread of AEEP.

Investigation of the polymer material perforation time: comparison between two fiber laser wavelengths

This study investigated the perforation time of polyamide 6.6 using fiber lasers at two different wavelengths: 1070 and 1943 nm. The novelty of this research lies in the comparison of perforation times at equivalent laser irradiances on the polymer sample with two different colors of polyamide 6.6: natural and black. The results revealed that, at comparable irradiance levels and beam diameters, the 1943 nm laser source perforated the polyamide 6.6 sample faster than the 1070 nm laser source. The difference in perforation time was found to be significantly higher for natural-colored polyamide 6.6 compared to black-colored polyamide 6.6. These findings suggest that, for material processing of polyamide 6.6, especially in terms of perforation, the use of 2 μm laser sources should be privileged over 1 μm laser sources.

Phase noise of a microwave photonic channel: direct-current versus external electro-optic modulation

We characterize the phase noise of a microwave photonic channel, where a 10 GHz signal is carried by an intensity-modulated light beam over a short optical fiber, and detected. Two options are compared: (i) an electro-optic modulator (EOM), and (ii) the direct modulation of the laser current. The 1.55 µm laser and the detector are the same. The effect of experimental parameters is investigated, the main being the microwave power and the laser bias current. The main result is that the upper bound of the phase flicker is −117dBrad2 in the case of the EOM, limited by the background noise of the setup. In contrast, with direct modulation of the laser, the flicker is of −114 to −100dBrad2, depending on the laser bias current (50–90 mA), and the highest noise occurs at the lowest bias. Our results are of interest in communications, radar systems, instrumentation, and metrology.

Diode-pumped Tm:YAP laser operating at 2.3 µm with enhanced performance through cascade lasing.

The laser diode (LD)-pumped Tm:YAP (a-cut, 3.5 at.%) laser generated a maximum ∼2.3 µm continuous wave (CW) laser output power of ∼3 W. The higher output power benefited from the positive effect of the cascade lasing (simultaneously operating on the 3H4 → 3H5 and 3F4 → 3H6 Tm3+ transition). It was the highest CW laser output power amongst the LD/Ti:Sapphire-CW-pumped ∼2.3 µm Tm3+-doped lasers reported so far. Under the cascade laser operation, the slope efficiency of the ∼2.3 µm laser emission versus the absorbed pump power increased from 13.0% to 21.4%.

Luminescent characteristics at ∼2.9 μm in Lu3+ modified Dy3+/Tm3+ co-doped LiYF4 single crystal

The single crystals specimens comprising 0.3 mol% Dy3+, 0.5 mol% Tm3+ and γ mol% Lu3+ doped LiYF4 (γ = 0, 0.3, 0.5, and 1.5) were meticulously synthesized using the Bridgman method, with the specific aim of catering to applications in the ∼2.9 μm laser domain. The microstructure of the obtained single crystal was investigated by conducting X-ray diffraction (XRD) measurements. The Judd-Ofelt (J-O) intensity parameters of the Dy3+ ion and the impacts of Lu3+ doping on fluorescence characteristics of the 6H13/2 (Dy3+) level were studied. The Dy3+/Tm3+ doped LiYF4 single crystal exhibits ∼52 % enhancement in emission intensity at ∼2.9 μm (Dy3+: 6H13/2→6H15/2) through a favorable introduction of Lu3+ ions into the single crystal at 808 nm LD excitation. The Tm3+/Dy3+/Lu3+ triply doped single crystal exhibited a maximum emission cross section of 2.480 × 10−20 cm2 at 2904 nm. The fluorescent lifetimes of the Dy3+: 6H13/2 level in the single crystals were determined to be located in the range of 2.78 ms–3.33 ms. The microscopic mechanism of energy transfer (ET) between Tm3+ and Dy3+ ions were investigated and the ET coefficients from 3H4 level of Tm3+ ion to 6F5/2 of Dy3+ ion (ET1) and 3F4 of Tm3+ to 6H11/2 of Dy3+ (ET2) in the triply doped single crystal were calculated, yielding values of 3.422 × 10−39 cm6/s and 5.768 × 10−39 cm6/s, separately. The results clearly demonstrated that the mid-infrared luminescence at ∼2.9 μm from Dy3+ ions can be significantly enhanced by the strategic incorporation of appropriate Lu3+ ions into Tm3+/Dy3+: LiYF4 single crystal.