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We demonstrated highly-efficient pulsed mid-infrared generation based on intracavity difference frequency mixing inside a continuous-wave (CW) PPLN optical parametric oscillator (OPO). The near-infrared pulsed fiber source was located at 1120 nm with variable pulse width and repetition rate. The pump source of OPO was a CW linearly-polarized high-power 1060 nm fiber laser. The 1120 nm and 1060 nm pump beams were simultaneously incident into the OPO cavity. The 1060 nm pump beam built parametric oscillation firstly and generated high-power resonant signal beam inside the cavity. By controlling the PPLN temperature properly, the phase-matched difference frequency generation (DFG) occurred between the signal beam and 1120 nm pulsed pump beam in the PPLN crystal. Finally, the pulsed 1120 nm pump beam was successfully transformed to 3593 nm mid-infrared radiation at every power level and temporal characteristic. Both the slope efficiency and pump-to-idler conversion efficiency of the intracavity DFG process reached over 20%. In addition, the pulse shape of newly generated 3593 nm idler beam was basically the same as 1120 nm pump beam. The experimental results exhibited huge potential in frequency down conversion of low-power laser sources with special temporal characteristics.

We have demonstrated the stable Q-switched Er-doped fluoride fiber laser with the help of the few-layered Ta2NiS5 in the mid-infrared spectral range. We fabricated the mid-infrared saturable absorber mirror (SAM) by depositing the layered Ta2NiS5 on a gold mirror. The layered Ta2NiS5 exhibited saturable absorption behavior with modulation depth 36% and saturation intensity 32.2 GW/cm2 at 2800 nm, respectively. With the Ta2NiS5-SAM, stable Q-switched pulses around 2.8 μm wavelength can be delivered with a pulse duration of 1.20 μs and a repetition rate of 102 kHz under an incident pump power of 860 mW from the ZBLAN fiber laser cavity. The experimental results confirm that Ta2NiS5 has great potentials as broadband saturable absorber in mid-infrared regions, paving the way for the application of low-dimensional ternary chalcogenide in broadband optoelectronic devices.

Based on an analysis of kinetic processes in the continuous-wave (CW) single-wavelength two-photon pumped Rb-vapor laser (Rb-TPAL), a three-dimensional computational model is established using the rate equation. Based on the application of the model to cavity-enhanced Rb-TPAL [Yuan et al., Optics Express 29, 4858 (2021)], the calculated and measured dependences of the laser power on the pump power show good agreement. We simulate the Rb-TPAL pumped by a high-power CW laser diode and analyze the effects of temperature, vapor cell length, pump waist, vapor cell transmission, and output mirror reflectance on the characteristics of the blue laser. The results suggest that the output power and efficiency of blue laser can be improved by optimizing the above parameters; however, the particles in the $5^{2}\text{D}_{5/2}$ level face difficulty to transition to the $6^{2}\text{P}_{3/2}$ level, and this limits the further improvement of blue laser efficiency; therefore, an approach is proposed to improve the efficiency of Rb-TPAL. This study can be useful for designing a two-photon pumped alkali metal laser with high-power output. [ABSTRACT FROM AUTHOR]

The airborne light detection and ranging (LiDAR) bathymetry (ALB) system is an extension of the ubiquitous topographic LiDAR mapping system and has been most simply characterized as adding a green laser to the infrared laser of topo systems. Due to the low point cloud density and monotonous objects in the scene, it is difficult to mosaicing the ALB strips. Therefore, the existing airborne laser scanning strip stitching algorithm has poor performance for ALB strips. In this article, a coarse-to-fine strip mosaicing model for ALB is proposed. The framework is fast and efficient and can handle large ALB data. An improved alpha shapes algorithm can fast and accurately determine the overlap region of strip is applied. Due to different data accuracy and spatial characteristics, the water area and land area are processed separately. A weight distribution-based coarse-to-fine registration model is designed for underwater areas. The topological constraint term is added to the nonrigid iterative closest point (ICP) cost function to prevent excessive deformation caused by outliers. The implicit B-spline surface fitting algorithm using the 3L algorithm and the least-squares trend surface fitting algorithm are applied separately to assign weights for overlapping strips to solve the limitation of no control or less control. Moreover, a random sample consensus (RANSAC)-ICP registration model characterized by the normal vector and curvature is constructed for land area. Finally, the comparisons with ICP highlight the superiority of the proposed approach in flexibility and accuracy. The root-mean-square error (RMSE) is 0.12 m and the maximum error is 0.36 m. [ABSTRACT FROM AUTHOR]

In this paper, a novel high efficient dual-wavelength mid-infrared optical parametric oscillator (OPO) was demonstrated, which was pumped by a dual-wavelength Raman fiber oscillator for the first time. The adoption of oscillator structure reduced the waste of power, increased Raman pump power and promoted its frequency conversion. The dual-wavelength pump source was fixed at 1070 nm and 1120 nm and the Raman conversion efficiency was greatly enhanced from 26.7% to 72.1%. The high Raman efficiency and low Raman threshold enabled the Raman laser to build optical parametric oscillation easily and the pump-to-idler conversion efficiency of Raman laser improved greatly from 4.2% to 13.3%. The generated dual-wavelength mid-infrared laser was fixed at 3272 nm and 3663 nm, with a maximum power of 6.87 W, indicating a 13.9% pump-to-idler conversion efficiency. The highest mid-infrared output power generated by optical parametric oscillation of Raman laser was also achieved, which is almost ten times than before.

The quantity security of stored grain in warehouses is crucial for a country. Since manual inspection of stored grain quantity is inefficient, some online automeasurement methods have been proposed recently, but they are either time-consuming or too expensive to be popularized. This article proposes a deep learning-based method to automatically monitor changes in grain quantity of granaries. First, the image of the same scene in a granary is taken at different moments using a device that integrates a camera and an infrared laser rangefinder. Then, a deep semantic segmentation model based on an encoder–decoder framework is developed to extract the grain loading line and grain surface of the image. Finally, the distance and area between the extracted grain loading line and grain surface are calculated and compared with the previous measured one to determine whether the grain quantity of the granary has changed. To improve the accuracy of the segmentation results, a novel reverse attention model is proposed to provide guidance information to fuse low-level features, which calculates multiscale attention maps based only on the output of the last layer of the encoder. Furthermore, the proposed method and infrared laser rangefinder-based method are combined to get more accurate grain volume after an abnormal change of grain quantity is detected by our method. Experimental results show that our method is effective and feasible for monitoring changes in grain quantity and outperforms the state-of-the-art methods on semantic segmentation. [ABSTRACT FROM AUTHOR]

We demonstrated highly-efficient pulsed mid-infrared generation based on intracavity difference frequency mixing inside a continuous-wave (CW) PPLN optical parametric oscillator (OPO). The near-infrared pulsed fiber source was located at 1120 nm with variable pulse width and repetition rate. The pump source of OPO was a CW linearly-polarized high-power 1060 nm fiber laser. The 1120 nm and 1060 nm pump beams were simultaneously incident into the OPO cavity. The 1060 nm pump beam built parametric oscillation firstly and generated high-power resonant signal beam inside the cavity. By controlling the PPLN temperature properly, the phase-matched difference frequency generation (DFG) occurred between the signal beam and 1120 nm pulsed pump beam in the PPLN crystal. Finally, the pulsed 1120 nm pump beam was successfully transformed to 3593 nm mid-infrared radiation at every power level and temporal characteristic. Both the slope efficiency and pump-to-idler conversion efficiency of the intracavity DFG process reached over 20%. In addition, the pulse shape of newly generated 3593 nm idler beam was basically the same as 1120 nm pump beam. The experimental results exhibited huge potential in frequency down conversion of low-power laser sources with special temporal characteristics. [ABSTRACT FROM AUTHOR]

Based on several centimeters long heavily Tm3+-doped germanate fibers (TGFs) and in-band-pumped technique, a short-wavelength distribute Bragg reflector (DBR) single-frequency fiber laser (SFFL) emitting at 1.7 μm is investigated experimentally. A stable single-longitudinal-mode laser output with a signal-to-noise ratio of greater than 60 dB and an operation wavelength of 1727 nm is realized. The maximum output power of 12.4 mW and the slope efficiency of 4.81% for the absorbed pump power are obtained from a 1.8-cm-long TGF pumped by a 1610 nm fiber laser. The measured relative intensity-noise of the SFFL reaches to around −130 dB/Hz at frequencies of over 10 MHz and the laser linewidth is 8.6 kHz. To the best of our knowledge, this is the first demonstration of the DBR Tm3+-doped SFFL with an operation wavelength in 1.7 μmregion. It is suitable for optical coherence tomography, methane gas detection and optical medical technology. [ABSTRACT FROM AUTHOR]

In this letter, we demonstrated a dual-wavelength (DW) mid-infrared optical parametric oscillator (OPO) that was pumped by two independent fiber lasers fixed at 1018 nm and 1080 nm, and realized phase-matched signal beam coupling by tuning grating period of PPLN. Based on signal beam coupling, two interesting phenomena were observed for the first time. One is that the OPO threshold for 1018 nm and 1080 nm pump beams could be drastically lowered from 15.4 W to 266 mW and from 13.5 W to 1.38 W separately. The other is that the total idler power obtained when the OPO was simultaneously pumped by two fiber lasers was higher than sum of idler power obtained when the OPO was independently pumped by two fiber lasers, revealing obvious parametric gain enhancement. It also indicated that the two independent OPO processes became coherent when two signal beams were coupled. The results exhibit great potential in practical applications such as frequency down-conversion of some special near-infrared laser sources such as pulsed single-frequency sources, spectrum high-speed swept sources, and ultra-short pulse sources with low duty cycle.

In this paper, a novel high efficient dual-wavelength mid-infrared optical parametric oscillator (OPO) was demonstrated, which was pumped by a dual-wavelength Raman fiber oscillator for the first time. The adoption of oscillator structure reduced the waste of power, increased Raman pump power and promoted its frequency conversion. The dual-wavelength pump source was fixed at 1070 nm and 1120 nm and the Raman conversion efficiency was greatly enhanced from 26.7% to 72.1%. The high Raman efficiency and low Raman threshold enabled the Raman laser to build optical parametric oscillation easily and the pump-to-idler conversion efficiency of Raman laser improved greatly from 4.2% to 13.3%. The generated dual-wavelength mid-infrared laser was fixed at 3272 nm and 3663 nm, with a maximum power of 6.87 W, indicating a 13.9% pump-to-idler conversion efficiency. The highest mid-infrared output power generated by optical parametric oscillation of Raman laser was also achieved, which is almost ten times than before. [ABSTRACT FROM AUTHOR]

Transcranial infrared laser stimulation (TILS) is a promising noninvasive intervention for neurological diseases. Though some experimental work has been done to understand the mechanism of TILS, the reported statistical analysis of data is quite simple and could not provide a comprehensive picture on the effect of TILS. This study learns the effect of TILS on hemodynamics of the human brain from experimental data using longitudinal data analysis methods. Specifically, repeated measures analysis of variance (ANOVA) is first applied to confirm the significance of the TILS effect and its characteristics. Based on that, two parametric mixed-effect models and non-parametric functional mixed-effect model are proposed to model the population-level performance and individual variation of this effect. Interpretations on the fitted models are provided, and comparison of the three proposed models in terms of fitting and prediction performance is made to select the best model. According to the selected model, TILS increases the concentration of oxygenated hemoglobin in the brain and this effect sustains even after the treatment stops. Also, there is considerable variation among individual responses to TILS. [ABSTRACT FROM AUTHOR]

We report on frequency down-conversion of dual-wavelength (DW) Raman fiber laser in a periodically poled lithium niobate-based optical parametric oscillator. The DW pump source was fixed at 1060 and 1111 nm that was obtained based on stimulated Raman scattering effect by combining a home-made linearly polarized 1060-nm fiber laser and 137-m-long polarization-maintaining passive fiber. The total pump power went through three stages, in the latter two of which the 1111-nm wave appeared. In the entire experiment, the 1060-nm pump beam achieved parametric oscillation and generated 1626-nm signal beam and 3056-nm idler beam. The 1111-nm pump beam generated 3503-nm idler beam based on difference frequency generation (DFG) between itself and 1626-nm signal beam in the second stage. With power enhancement, it built independent parametric oscillation in the third stage and generated 1621-nm signal beam as well as 3530-nm idler beam. The DW idler power ranged from 3.94 to 7.78 W in the latter two stages. The power and efficiency characteristics in frequency conversion processes of 1060- and 1111-nm pump beams were also analyzed separately.

We report, to the best of our knowledge, the first demonstration of a continuous-wave, dual-wavelength (DW) mid-infrared optical parametric oscillator (OPO) based on the stimulated Raman scattering (SRS) effect of periodically poled lithium niobate (PPLN). The OPO was pumped by two independent fiber lasers, one being fixed at 1018 nm and the other being tunable. The high-power 1018-nm source built parametric oscillation, induced SRS effect in PPLN and generated 1495-nm signal beam as well as 1506-nm Raman beam. The tunable fiber laser was set at 1080 nm and the phase-matched difference frequency generation (DFG) occurred between the 1506-nm Raman beam and 1080-nm pump beam. Finally, DW idler beam located at 3189 and 3819 nm was obtained whose power ranged from 8.044 to 8.115 W, in which the 3189-nm idler power made up the majority of about 8 W and the maximum 3819-nm idler power reached 0.154 W. The slope and conversion efficiency of DFG and OPO processes was also discussed separately.

The impact of scaling of the base layer on the noise performance, spectral responsivity, and frequency response of Ge/Ge1–xSnx/Ge p-n-p heterojunction phototransistor (HPT) is presented and evaluated by simulation. The proposed structure consists of Ge1–xSnx alloy in the base layer, allowing extension of the photodetection to the mid-infrared (MIR) region, enabling photodetection over a wide range. This paper also includes the effect of Sn concentration and base bias voltage on the frequency performance of the HPT. In addition, various noise components and signal-to-noise ratio (SNR) are estimated as a function of base layer thickness and base resistance. The simulated results show that cutoff frequency (${f}_{T}$) and maximum frequency (${f}_{\text {max}}$) are not only strongly dependent on the base layer thickness but also on the Sn composition in the base layer and applied base-bias voltage. The results show that the proposed HPT provides higher ${f}_{T} >45$ GHz and SNR of >70 dB for the base layer thickness of 50 nm (with Sn = 9%) can be achieved. Therefore, the GeSn p-n-p HPT is promising for future fiber-optic telecommunication and MIR applications. [ABSTRACT FROM AUTHOR]

The state-of-the-art long-distance near-infrared optical radars use laser-diode-based miniature pulsed transmitters producing optical pulses of 3–10 ns in duration and peak power typically below 40 W. The duration of the transmitted optical pulses becomes a bottleneck in the task of improving the radar ranging precision, particularly due to the progress made in developing single photon avalanche detectors. The speed of miniature high-current drivers is limited by the speed of the semiconductor switch, either a gallium nitride field-effect transistor, the most popular alternative nowadays, or a silicon avalanche bipolar junction transistor (ABJT), which was traditional in the past. Recent progress in the physical understanding of peculiar 3-D transients promises further enhancement in speed and efficiency of properly modified ABJTs, but that is not the only factor limiting the transmitter speed. We show here that a low-inductance miniature transmitter assembly containing only a specially developed capacitor, a more advanced transistor chip than that used in commercial ABJTs and a laser diode, has allowed peak power from 40 to 180 W to be reached in optical pulses of 1–2 ns in duration without after-pulsing relaxation oscillations. This finding is of interest for compact low-cost, long-distance decimeter-precision lidars, particularly for automotive applications. [ABSTRACT FROM AUTHOR]

A mode-locked laser with orthogonal polarization at the wavelength of 1342 nm is experimentally achieved by using the natural birefringence of the Nd:YVO4 crystal. A total output power of 2.64 W could be obtained at an incident power of 14.4 W and the pulse durations are measured to be 15.1 and 16.9 ps with pulse repetition rates of 6.0 and 6.45 GHz for the laser output along the π- and σ-polarization, respectively. The mode-locked output is further found to exhibit a complex temporal trace with beat frequencies originated from the different central frequencies and pulse repetition rates.

We report a multiwavelength mid-infrared laser based on intracavity difference frequency generation in an MgO-doped periodically poled LiNbO3 optical parametric oscillator, which was pumped by a dual-wavelength fiber MOPA consisting of two parts: dual-wavelength seed and power amplifier. The maximum output power of the linearly polarized pump laser was 65.3 W, and the wavelengths were 1060 and 1080 nm. Three idler emissions with different wavelengths of 3127, 3303 and 3346 nm were obtained under the maximum pump power, and the total idler output reached 7.38 W, indicating a 15% pump-to-idler slope efficiency. The signal laser generated in the experiment had two wavelengths, which were 1594 and 1604 nm under the maximum pump power. Three nonlinear progresses occurred in the experiment, two of them being optical parametric oscillation and the one left being difference frequency generation.

We report on a high-peak-power acousto-optically Q-switched Er:Y2O3 ceramic laser operating at room temperature. Stable pulses with a duration of 41-190 ns (FWHM) are generated at approximately 2.7 μm with the repetition rate varying from 0.3 to 10 kHz. The peak power at 0.3-kHz repetition rate is approximately 7.3 kW. An average output power of over 320 mW is generated at a repetition rate of 10 kHz using an output coupler with a transmission of 8%.

InP-etched facet ridge lasers emitting in the optical C-band are heterogeneously integrated on Si substrates by microtransfer printing for the first time. 500 μm × 60 μm laser coupons are fabricated with a highly dense pitch on the native InP substrate. The laser epitaxial structure contains a 1-μm-thick InGaAs sacrificial layer. A resist anchoring system is used to restrain the devices while they are released by selectively etching the InGaAs layer with FeCl3:H2O (1:2) at 8 °C. Efficient thermal sinking is achieved by evaporating Ti-Au on the Si target substrate and annealing the printed devices at 300 °C. This integration strategy is particularly relevant for lasers being butt coupled to polymer or silicon-on-insulator (SOI) waveguides.

A diode-end-pumped actively Q-switched Nd:YAP laser at 1080 nm is originally designed to intracavity pump a Potassium Titanyl Phosphate KTiOPO4 (KTP)-based optical parametric oscillator for obtaining the signal wavelength at 1603 nm. Under an absorbed pump power value of 11 W, the maximum average output power at the eye-safe radiation is efficiently generated to be 1.11 W at a pulse repetition rate of 10 kHz. At a pulse repetition rate of 5 kHz, the shortest pulse duration, the largest pulse energy, and the highest peak power are found to be 2.4 ns, 190 μJ, and 67.3 kW, respectively. In addition, the influence of energy-transfer upconversion effect on the capability of power scaling of the developed Nd:YAP fundamental laser is experimentally investigated and theoretically analyzed.

A diode-pumped dual-wavelength CW Tm, Ho: YAG ceramic laser was demonstrated for the first time to our knowledge. A maximum output power of ~1.2 W with a beam quality factor M2 = 1.19 has been generated from the 3at.% Tm, 0.5at.% Ho: YAG ceramic, corresponding to a slope efficiency of 16.7% with respect to the absorbed pump power. This Tm, Ho: YAG ceramic laser operated at dual-wavelengths around 2090 and 2096 nm. With the increase in the absorbed pump power and the output coupler transmittance, blue-shift of the emission wavelength was observed.

We report, to the best of our knowledge, the first demonstration of a continuous-wave, dual-wavelength (DW) mid-infrared optical parametric oscillator (OPO) based on the stimulated Raman scattering (SRS) effect of periodically poled lithium niobate (PPLN). The OPO was pumped by two independent fiber lasers, one being fixed at 1018 nm and the other being tunable. The high-power 1018-nm source built parametric oscillation, induced SRS effect in PPLN and generated 1495-nm signal beam as well as 1506-nm Raman beam. The tunable fiber laser was set at 1080 nm and the phase-matched difference frequency generation (DFG) occurred between the 1506-nm Raman beam and 1080-nm pump beam. Finally, DW idler beam located at 3189 and 3819 nm was obtained whose power ranged from 8.044 to 8.115 W, in which the 3189-nm idler power made up the majority of about 8 W and the maximum 3819-nm idler power reached 0.154 W. The slope and conversion efficiency of DFG and OPO processes was also discussed separately. [ABSTRACT FROM AUTHOR]

We report on frequency down-conversion of dual-wavelength (DW) Raman fiber laser in a periodically poled lithium niobate-based optical parametric oscillator. The DW pump source was fixed at 1060 and 1111 nm that was obtained based on stimulated Raman scattering effect by combining a home-made linearly polarized 1060-nm fiber laser and 137-m-long polarization-maintaining passive fiber. The total pump power went through three stages, in the latter two of which the 1111-nm wave appeared. In the entire experiment, the 1060-nm pump beam achieved parametric oscillation and generated 1626-nm signal beam and 3056-nm idler beam. The 1111-nm pump beam generated 3503-nm idler beam based on difference frequency generation (DFG) between itself and 1626-nm signal beam in the second stage. With power enhancement, it built independent parametric oscillation in the third stage and generated 1621-nm signal beam as well as 3530-nm idler beam. The DW idler power ranged from 3.94 to 7.78 W in the latter two stages. The power and efficiency characteristics in frequency conversion processes of 1060- and 1111-nm pump beams were also analyzed separately. [ABSTRACT FROM AUTHOR]

The frequencies for thirty one far-infrared laser emissions, generated by an optically pumped molecular laser with either 13CD3OH or CH3 18OH as its laser medium, have been measured for the first time. The frequencies, ranging from 0.443 to 3.243 THz, were measured with a heterodyne technique to a one-sigma fractional uncertainty no less than ± 5 parts in 107. Approximately half of the frequencies measured during this investigation have been used to either confirm or propose new spectroscopic assignments associated with these methanol isotopologues. [ABSTRACT FROM AUTHOR]

We present a timing jitter and amplitude noise characterization of a high-power mode-locked integrated external-cavity surface emitting laser (MIXSEL). In the MIXSEL, the semiconductor saturable absorber of a SESAM is integrated into the structure of a VECSEL to start and stabilize passive mode-locking. In comparison to previous noise characterization of SESAM-mode-locked VECSELs, this first noise characterization of a MIXSEL is performed at a much higher average output power. In a free-running operation, the laser generates 14.3-ps pulses at an average output power of 645 mW at a 2-GHz pulse repetition rate and an RMS amplitude noise of 0.15% [1 Hz, 10 MHz]. We measured an RMS timing jitter of 129 fs [100 Hz, 10 MHz], which represents the lowest value for a free-running passively mode-locked semiconductor disk laser to date. Additionally, we stabilized the pulse repetition rate with a piezo actuator to control the cavity length. With the laser generating 16.7-ps pulses at an average output power of 701 mW, the repetition frequency was phase-locked to a low-noise electronic reference using a feedback loop. In actively stabilized operation, the RMS timing jitter was reduced to less than 70 fs [1 Hz, 100 MHz]. In the 100-Hz to 10-MHz bandwidth, we report the lowest timing jitter measured from a passively mode-locked semiconductor disk laser to date with a value of 31 fs. These results show that the MIXSEL technology provides compact ultrafast laser sources combining high-power and low-noise performance similar to diode-pumped solid-state lasers, which enable world-record optical communication rates and low-noise frequency combs.

We demonstrate the first InGaN-LD-pumped room temperature and continuous-wave laser operation of a Pr3+: LiYF4 crystal at 915 nm. A maximum output power up to 78 mW with a laser slope efficiency of about 17% is obtained. The round-trip optical losses are estimated to be about 0.45%, and the M2 beam quality factors measured in x and y dimensions are about 1.07 and 1.04, respectively.

We demonstrate the first multiwavelength Brillouin-thulium fiber laser (BTFL) with wavelengths near 1.97 μm. The multiwavelength fiber laser was realized based on stimulated Brillouin scattering and nonlinear polarization rotation effects. The laser can generate five Brillouin wavelengths with spacing of about 0.105 nm, which is identical with the wavelength spacing of adjacent Brillouin Stokes lines. The peak power fluctuations of the multiwavelength BTFL were less than 0.5 dB, and the wavelength shifts were less than 0.01 nm in 20 min.

Laser drilling has been adapted for forming a hole to connect between layers of multilayered printed circuit board (PCB). Many manufacturers have adapted CO2 lasers to achieve process throughputs with blind via hole (BVH) diameter greater than 75 \mu \textm . However, slimmer and lighter electronic devices that require sub-50- \mu \textm BVHs and CO2 laser have a limitation due to the nature of their characteristics. A near-infrared (IR) laser is a good alternative to form sub-50- \mu \textm BVHs, but far too little attention has been paid to BVH drilling with the near-IR laser. This paper applied picosecond IR pulsed laser to create BVH on copper-coated glass/epoxy. Smear zone, top and bottom hole diameters, and taper ratio are investigated as a function of the total fluence. The result shows that the sub-50- \mu \textm BVHs can be achieved with picosecond IR pulsed laser. [ABSTRACT FROM PUBLISHER]

We report on a high-peak-power acousto-optically Q-switched Er:Y2O3 ceramic laser operating at room temperature. Stable pulses with a duration of 41–190 ns (FWHM) are generated at approximately 2.7 μm with the repetition rate varying from 0.3 to 10 kHz. The peak power at 0.3-kHz repetition rate is approximately 7.3 kW. An average output power of over 320 mW is generated at a repetition rate of 10 kHz using an output coupler with a transmission of 8%. [ABSTRACT FROM PUBLISHER]

In recent years, additive manufacturing has experienced rapid growth, due to its inherent capabilities for creating arbitrary 3-D structures, accessibility, and associated low manufacturing costs. This paper first reviews the state of the art in 3-D printing for terahertz (THz) applications and identifies the critical features required for such applications. The future potential for this technology is demonstrated experimentally with the first 3-D-printed, optically controlled THz IQ vector modulator. Here, miniature high-resistivity silicon implants are integrated into metal-pipe rectangular waveguides. The 3-D-printed split-block assembly also houses two packaged infrared laser diodes and a heat sink. The measured performance of a proof-of-principle 4-quaternary amplitude modulation (4-QAM) vector modulator that operates up to 500 GHz is reported. This new hybrid 3-D printing THz technology, which combines semiconductor devices with potentially low-cost, high-performance passive guided-wave structures represents a paradigm shift and may prove to be an ideal solution for implementing affordable transceivers in future ubiquitous THz applications. [ABSTRACT FROM AUTHOR]

We provide a theoretical analysis of the relative merits of tensile strain and n-type doping as approaches to realizing an efficient low-power germanium laser. Ultimately, tensile strain offers threshold reductions of over 200x, and significant improvements in slope efficiency compared with the recently demonstrated 0.25% strained electrically pumped germanium laser. In contrast, doping offers fundamentally limited benefits, and too much doping is harmful. Moreover, we predict that tensile strain reduces the optimal doping value and that experimentally demonstrated doping has already reached its fundamental limit. We therefore theoretically show large (>; 1%) tensile strain to be the most viable path to a practical germanium-on-silicon laser.

We present timing jitter measurements of an InGaAs quantum well vertical external cavity surface emitting laser (VECSEL) passively mode locked with a quantum dot semiconductor saturable absorber mirror (SESAM) at 2-GHz repetition rate. It generates 53-mW average output power in 4.6-ps pulses at 953 nm. The laser housing was optimized for high mechanical stability to reduce acoustic noise. We use a fiber-coupled multimode 808-nm pump diode, which is mounted inside the laser housing. No active cavity length stabilization is employed. The phase noise of the free-running laser integrated over a bandwidth from 100 Hz to 1 MHz corresponds to an RMS timing jitter of ≈212 fs, which is lower than previously obtained for mode-locked VECSELs. This clearly confirms the superior noise performance expected from a high-Q-cavity semiconductor laser. In contrast to edge-emitting semiconductor diode lasers, the cavity mode is perpendicular to the quantum well gain layers, which minimizes complex dispersion and nonlinear dynamics.

We review breakthroughs in the area of mid-infrared laser development. We summarize 2009 research across a broad range of mid-infrared laser technologies, including bulk solid-state lasers, fiber lasers, and nonlinear optics for the generation of infrared light between 2 and 8 $\mu\hbox{m}$ .

A high-current and low on-state voltage optical Darlington transistor (ODT) is developed in this paper for high-power applications. The structure of this device includes a two-stage Darlington transistor in which the first stage is triggered optically using an infrared laser of an 808-nm wavelength. The photogenerated current in the first stage drives the second stage of the ODT for current amplification. The ON-state voltage of the proposed two-stage ODT is found to be 1.12 V at 50 A. The results show that a single-pipe laser with a low optical power of 2 W is sufficient to trigger this high-current optical switch. This can give us more flexibility to achieve an optimal tradeoff between the ON-state voltage and delay times. The experimental results show that the ODT has a breakdown voltage of 70 V and can operate at frequencies higher than 10 kHz. Thismakes it potentiallysuitable as an optical gate driver for applications including but not limited to pulsed-power and series-connectionof power semiconductor devices for voltage scaling, and as an auxiliary optical-triggering device for anode- or even gate-currentmodulation of a high-frequency and high-power all-optical emitter turn-OFF thyristor. [ABSTRACT FROM AUTHOR]

We report a multiwavelength mid-infrared laser based on intracavity difference frequency generation in an MgO-doped periodically poled LiNbO3 optical parametric oscillator, which was pumped by a dual-wavelength fiber MOPA consisting of two parts: dual-wavelength seed and power amplifier. The maximum output power of the linearly polarized pump laser was 65.3 W, and the wavelengths were 1060 and 1080 nm. Three idler emissions with different wavelengths of 3127, 3303 and 3346 nm were obtained under the maximum pump power, and the total idler output reached 7.38 W, indicating a 15% pump-to-idler slope efficiency. The signal laser generated in the experiment had two wavelengths, which were 1594 and 1604 nm under the maximum pump power. Three nonlinear progresses occurred in the experiment, two of them being optical parametric oscillation and the one left being difference frequency generation. [ABSTRACT FROM PUBLISHER]

We report a two-stage diode-pumped Er-doped fiber amplifier operating at the wavelength of 1550 nm at the repetition rate of 10–100 kHz with an average output power of up to 10 W. The first stage comprising Er-doped fiber was core-pumped at the wavelength of 1480 nm, whereas the second stage comprising double-clad Er/Yb-doped fiber was clad-pumped at the wavelength of 975 nm. The estimated peak power for the 0.4-nm full-width at half-maximum laser emission at the wavelength of 1550 nm exceeded 4-kW level. The initial 100-ns seed diode laser pulse was compressed to 3.5 ns as a result of the 34-dB total amplification. The observed 30-fold efficient pulse compression reveals a promising new nonlinear optical technique for the generation of high power short pulses for applications in eye-safe ranging and micromachining. [ABSTRACT FROM PUBLISHER]

The C-13 methanol isotopologues 13CH3OH, 13CD3OD, and 13CHD2OH have individually served as the laser medium for an optically pumped molecular laser system used to generate far-infrared radiation. Once detected the frequencies of these laser emissions were measured using a heterodyne technique to a one-sigma fractional uncertainty no less than ± 5 parts in 107. In total, 60 far-infrared laser frequencies, ranging from 0.355 to 2.817 THz, have been measured for the first time. One of these laser emissions was discovered during this investigation and is reported with its polarization with respect to the CO2 pump laser, output power, and optimal operating pressure. In several cases, these measured laser frequencies are in excellent agreement with the calculated values, as determined through combination-loop relations, further confirming the proposed spectroscopic assignments. [ABSTRACT FROM PUBLISHER]

The performance of mid-infrared Er3+-doped fiber lasers has dramatically improved in the last few years. In this paper, we present a numerical model that provides valuable insight into the dynamics of a dual-wavelength pumped fiber laser that can operate on the 3.5- and 2.8- \mu \textm bands. This model is a much needed tool for optimizing and understanding the performance of these laser systems. Comparisons between simulation and experimental results for three different systems are presented. [ABSTRACT FROM PUBLISHER]

We report the high-energy flat-top supercontinuum covering the midinfrared wavelength range of 1.9–2.5 μm as well as electronically tunable femtosecond pulses between 1.98 and 2.22 μm directly from the thulium-doped fiber laser amplifier. Comparison of experimental results with numerical simulations confirms that both sources employ the same nonlinear optical mechanism—Raman soliton frequency shift occurring inside the Tm-fiber amplifier. To illustrate that we investigate two versions of the compact diode-pumped SESAM mode-locked femtosecond thulium-doped all-silica-fiber-based laser system providing either broadband supercontinuum or tunable Raman soliton output, depending on the parameters of the system. The first system operates in the Raman soliton regime providing femtosecond pulses tunable between 1.98 and 2.22 μm. Wide and continuous spectral tunability over 240 nm was realized by changing only the amplifier pump diode current. The second system generates high-energy supercontinuum with the superior spectral flatness of better than 1 dB covering the wavelength range of 1.9–2.5 μm, with the total output energy as high as 0.284 μJ, and the average power of 2.1 W at 7.5-MHz repetition rate. We simulate the amplifier operation in the Raman soliton self-frequency shift regime and discuss the role of induced Raman scattering in supercontinuum formation inside the fiber amplifier. We compare this system with a more traditional 1.85–2.53-μm supercontinuum source in the external highly-nonlinear commercial chalcogenide fiber using the Raman soliton MOPA as an excitation source. The reported systems1 1

Patent pending, ATLA Lasers AS, Trondheim, Norway. [ABSTRACT FROM PUBLISHER]

This paper investigated a method to cure silicone encapsulant in a light-emitting diode (LED) package by irradiating infrared ( $\lambda = 980$ nm) laser in order to reduce phosphor precipitation in LED packaging process. When the laser is irradiated on a silicone encapsulant with phosphor, phosphor is directly heated, and then its thermal energy is transferred to the encapsulant. We optimized the output and irradiation time of the infrared laser adopted in the curing process and compared the characteristics of silicone encapsulant cured by the infrared laser to those cured by a convection oven. We show that phosphor precipitation is reduced when the silicone encapsulant is cured with the infrared laser curing, which resulted in a decrease in color coordinate deviation and an increase in luminous efficiency. [ABSTRACT FROM PUBLISHER]

A diode-end-pumped actively $Q$-switched Nd:YAP laser at 1080 nm is originally designed to intracavity pump a Potassium Titanyl Phosphate KTiOPO4 (KTP)-based optical parametric oscillator for obtaining the signal wavelength at 1603 nm. Under an absorbed pump power value of 11 W, the maximum average output power at the eye-safe radiation is efficiently generated to be 1.11 W at a pulse repetition rate of 10 kHz. At a pulse repetition rate of 5 kHz, the shortest pulse duration, the largest pulse energy, and the highest peak power are found to be 2.4 ns, 190 \mu\text{J}, and 67.3 kW, respectively. In addition, the influence of energy-transfer upconversion effect on the capability of power scaling of the developed Nd:YAP fundamental laser is experimentally investigated and theoretically analyzed. [ABSTRACT FROM PUBLISHER]

We report and compare three configurations of the semiconductor saturable absorber mirror mode-locked, linear cavity femtosecond all-fiber master oscillator power amplifier based on a highly Ge-doped thulium-doped normal dispersion fibers. We have studied the performance of the system and have obtained stable mode-locking in a wide cavity dispersion range \sim 1.88~\mu \textm . In this letter, we focus our attention on three mode-locking regimes: laser operating in the anomalous, nearly zero and normal cavity dispersion regimes without the use of the additional dispersion compensating elements. For the nearly zero and normal cavity dispersion regimes the femtosecond pulses with several nanojoule energy could be obtained. The pulses were further compressed down to 630 fs using a simple fiber compressor consisting of a piece of the conventional telecommunication fiber, making the laser design particularly simple and cost effective. [ABSTRACT FROM PUBLISHER]

This paper presents a technique and initial conditions for the laser ablation of microstructures in a low temperature co-fired ceramic (LTCC) technology. It is demonstrated that 2.5-D microstructures can be realized cost effectively and precisely by deploying the proposed technique in which an infrared laser is used to carefully ablate portions of unfired LTCC green tape. A demonstration prototype consisting of three gears and their mounting platform is realized along with a detailed description of the attendant micromachining process. The ablated surface is examined using a scanning electron microscope and a surface profiler. The optimization of the laser parameters required to equalize the surface roughness of the ablated material to that of an unmachined LTCC substrate is also described. [ABSTRACT FROM PUBLISHER]

We demonstrate the first InGaN-LD-pumped room temperature and continuous-wave laser operation of a Pr3+:LiYF4 crystal at 915 nm. A maximum output power up to 78 mW with a laser slope efficiency of about 17% is obtained. The round-trip optical losses are estimated to be about 0.45%, and the M2 beam quality factors measured in x and y dimensions are about 1.07 and 1.04, respectively. [ABSTRACT FROM AUTHOR]

The reinvestigation of 13CD3OH, 13CD3OD, CD3CN, and 13CD3I as far-infrared lasing media has been performed with an optically pumped molecular laser system utilizing a transverse pumping geometry. Thirty-four far-infrared laser emissions, with wavelengths ranging from 55.0 to 873.2 μm, have been discovered with this system. Each new laser emission is reported with its wavelength, optimal operating pressure, polarization with respect to the CO2 pump laser, and power. When possible, the offset frequency of the CO2 pump laser with respect to its center frequency was determined using the reported offset frequencies for known far-infrared laser emissions. Four of the laser emissions discovered for 13CD3OH and 13CD3OD are consistent with the wavelengths predicted from the tentative spectroscopic assignments of far-infrared laser schemes. [ABSTRACT FROM AUTHOR]

We report the demonstration of high-average-power passively Q-switched laser oscillation from Fe2+ ions in zinc selenide. A semiconductor saturable absorber mirror was used as a passive Q-switch element. Using a 60% R outcoupler, the pump-limited output power was 515 mW. The spectral center of the laser was 4045 nm. The pulse repetition frequency (PRF) at maximum power was ~ 850 kHz with a corresponding minimum pulsewidth of 64 ns Full-Width Half-Maximum. The pulse energy and peak power were and 8.3 W, respectively. The average output power was limited only by available pump power and increased with a slope efficiency of 22%. No thermal rolloff of slope-efficiency was observed. The beam quality was measured to be M2 ≤ 2.6. The temporal stability of the pulsed output was characterized. Thermal effects were shown to play a significant role in determining the PRF of the output. [ABSTRACT FROM PUBLISHER]

We present a timing jitter and amplitude noise characterization of a high-power mode-locked integrated external-cavity surface emitting laser (MIXSEL). In the MIXSEL, the semiconductor saturable absorber of a SESAM is integrated into the structure of a VECSEL to start and stabilize passive mode-locking. In comparison to previous noise characterization of SESAM-mode-locked VECSELs, this first noise characterization of a MIXSEL is performed at a much higher average output power. In a free-running operation, the laser generates 14.3-ps pulses at an average output power of 645 mW at a 2-GHz pulse repetition rate and an RMS amplitude noise of 0.15% [1 Hz, 10 MHz]. We measured an RMS timing jitter of 129 fs [100 Hz, 10 MHz], which represents the lowest value for a free-running passively mode-locked semiconductor disk laser to date. Additionally, we stabilized the pulse repetition rate with a piezo actuator to control the cavity length. With the laser generating 16.7-ps pulses at an average output power of 701 mW, the repetition frequency was phase-locked to a low-noise electronic reference using a feedback loop. In actively stabilized operation, the RMS timing jitter was reduced to less than 70 fs [1 Hz, 100 MHz]. In the 100-Hz to 10-MHz bandwidth, we report the lowest timing jitter measured from a passively mode-locked semiconductor disk laser to date with a value of 31 fs. These results show that the MIXSEL technology provides compact ultrafast laser sources combining high-power and low-noise performance similar to diode-pumped solid-state lasers, which enable world-record optical communication rates and low-noise frequency combs. [ABSTRACT FROM PUBLISHER]

In this paper, a theoretical analysis of unstrained GeSn alloys as a laser gain medium was performed. Using the empirical pseudopotential method, the band structure of GeSn alloys was simulated and verified against experimental data. This model shows that GeSn becomes direct bandgap with 6.55% Sn concentration. The optical gain of GeSn alloys with 0–10% Sn concentration was calculated with different n-type doping concentrations and injection levels. It is shown theoretically that adding Sn greatly increases the differential gain owing to the reduction of energy between the direct and indirect conduction bands. For a double-heterostructure laser, the model shows that at a cavity loss of 50 cm^-1, the minimum threshold current density drops 60 times from Ge to Ge0.9Sn0.1, and the corresponding optimum n-doping concentration of the active layer drops by almost two orders of magnitude. These results indicate that GeSn alloys are good candidates for a Si-compatible laser. [ABSTRACT FROM PUBLISHER]

We discuss the design of mid-infrared quantum cascade lasers in which the emission frequency can be rapidly modulated by applied bias voltage. The devices are based on integrating a layer with voltage-variable refractive index, based on Stark-tunable inter-sub-band transitions, below the laser active region. A three-terminal configuration is used to independently bias the laser active region and the refractive index variation layer. The ultimate performance of the proposed scheme is analyzed theoretically and proof-of-principle devices are demonstrated experimentally. Experimentally, \lambda\approx 10∼\mum lasers demonstrate up to 4.5-GHz frequency tuning at a temperature of 80 K. [ABSTRACT FROM AUTHOR]