2.09†µm high-gain, high-energy sub-nanosecond laser amplification system and its application to a millijoule-level mid-infrared ZnGeP2 optical parametric generator.

In this Letter, we report for the first time to our knowledge a 2 mJ-level 2.09 µm Ho:YAG regenerative amplifier (RA) seeded by the first-stage Ho-doped fiber (HDF) preamplifier of a gain-switched laser diode (GSLD). After the single-pass power amplifier (SPPA), the output of a 2.09 µm pulse laser with 1 kHz, 570 ps, and >10 mJ was achieved. The overall gain of the whole amplifier system was greater than 90 dB, providing a novel, stable, and reliable sub-nanosecond (sub-ns) pump source operating at a pulse repetition frequency (PRF) of 1 kHz for an optical parametric generator (OPG) based on ZnGeP2 (ZGP). Specifically, for the ZGP OPG structure, a maximum pulse energy of 1.82 mJ at 3-5 µm had been achieved with an injected pump pulse energy of 5.47 mJ, corresponding to a slope efficiency of 39.5% and an optical-to-optical conversion efficiency (OOCE) of 33.27%.

Narrowband mid-infrared optical parametric generator based on a type-II BaGa4Se7 crystal.

In this Letter, we first reported on a mid-infrared double-pass optical parametric generator (OPG) based on a single type-II phase-matching BaGa4Se7 (BGSe) crystal, pumped at 2.1 µm. The OPG achieved a maximum pulse energy of 55 µJ for generating narrowband mid-infrared laser pulses. The signal and idler lights exhibited center wavelengths of 4.04 and 4.33 µm, respectively, with bandwidths of 18.6 nm (11.4 cm-1) and 20.4 nm (10.9 cm-1). To improve the output performance, we utilized a cascaded scheme of type-I ZnGeP2 (ZGP) and type-II BGSe crystals. The spectral bandwidths of the signal and idler lights, nearing 4 µm, were narrower than 170 nm (90 cm-1), representing a significant improvement over the ZGP OPG. The cascaded OPG achieved a remarkable total optical-to-optical conversion efficiency (OOCE) of 14.9% and a maximum pulse energy of 0.329 mJ.

113 W Ho:YLF oscillator with good beam quality efficiently pumped by a Tm:YAP laser.

We demonstrate a linearly polarized Tm:YAP slab laser pumped by fiber-coupled laser diodes. The maximum output power is 202 W at 1937.5 nm with a slope efficiency of 47.4% and an optical-to-optical efficiency of 35.6%. The beam quality M2 factors are 10.1 and 8.33 in x and y directions, respectively. Using the Tm:YAP laser as the pump source, the maximum power of the Ho:YLF oscillator is 113 W at 2063.3 nm, corresponding to an optical-to-optical efficiency of 55.9%. In addition, the beam quality factors of the Ho:YLF laser are ∼1.5 at maximum power.

Thermal-birefringence-induced depolarization in a 450 W Ho:YAG MOPA system.

We demonstrated an efficient, high-power Ho:YAG master-oscillator power amplifier (MOPA) system and investigated its thermal-birefringence-induced depolarization. The maximum output power was 450 W with a depolarized power of 32.1 W and depolarization of 0.071 via three power amplifiers. To our knowledge, this is the highest average power generated from a Ho:YAG MOPA system. In theory, a simplified model was built to calculate the depolarization in the amplifier, and the theoretical results agreed with the actual value well. Moreover, the overall optical-to-optical efficiency of the MOPA system was near 60%, and the beam quality M2 factors of s-polarized laser were measured to be ∼ 1.8 at 400 W. In pulse operation, the per pulse energy was ∼ 11 mJ at the pulse repetition frequency of 40 kHz with the corresponding peak power of 220 kW.

Twenty-four hour variability of inverted T-waves in patients with apical hypertrophic cardiomyopathy.

Background: Patients with apical hypertrophic cardiomyopathy (ApHCM) have marked inverted T-waves that vary over several years. Inverted T-waves in ApHCM are unstable, but it is unclear whether this change is due to coronary artery disease (CAD) or if it is a characteristic of ApHCM itself. We aimed to study the characteristics of inverted T-waves in patients with ApHCM over the course of 24 h to improve the diagnostic indices of ApHCM. Methods: We examined 83 patients with ApHCM and 89 patients with CAD (who served as the control group). All patients underwent a 24-h dynamic electrocardiogram (ECG). We analyzed the average depth of inverted T-waves per minute and sorted them from shallow to deep; the sorted ECG segments at the 10th, 50th, and 90th positions of the T-wave were subsequently analyzed. Results: The amplitudes of inverted T-waves in ApHCM corresponding to the 10th, 50th, and 90th percentiles were -5.13 ± 4.11, -8.10 ± 4.55, and -10.9 ± 5.04 mm, respectively. Changes in the degree of inverted T-waves were greater in ApHCM than in CAD. T-wave amplitudes in ApHCM were strongly associated with heart rate and circadian rhythm and only weakly associated with CAD and posture. Maximum T-wave amplitudes in the CAD group were <10 mm, while 68% of patients with ApHCM had maximum T-wave amplitudes >10 mm, and all patients with ApHCM aged <50 years had maximum T-wave amplitudes >10 mm. Conclusion: Notable variations in the T-waves of patients with ApHCM were observed over 24 h. ECG examinations during states of inactivity (comparable to sleep) improved the sensitivity of the diagnosis of ApHCM. Inverted T-wave amplitudes correlated with heart rate and circadian rhythm, where T-wave changes in ApHCM may be due to the normalization of abnormal T-waves effect. Identifying T-wave amplitudes >10 mm can effectively improve the diagnostic rate of ApHCM, especially in patients aged <50 years. The short-term change in T-waves in patients with ApHCM could serve as a novel index that will help in the diagnosis of ApHCM.

High Performance Hall Sensors Built on Chemical Vapor Deposition-Grown Bilayer Graphene.

Graphene has been considered as an excellent channel material for constructing magnetic sensors or Hall elements with high sensitivity and linearity. Compared to intensively reported graphene Hall elements (GHEs) fabricated on monolayer graphene, the exploration on bilayer graphene-based Hall elements is very rare. Here, we first investigate the performance and potential of Hall elements built on chemical vapor deposition-grown bilayer graphene. Without applying any gate voltage, the bilayer GHEs exhibit a typical voltage sensitivity of 119 mV/VT and current sensitivity of 397 V/AT, which are higher than those in the monolayer GHEs, indicating the better performance in practical applications. Moreover, the bilayer GHEs present obviously lower noise and then the minimum detection magnetic field compared to the monolayer ones. Hall elements built on bilayer graphene show certain unique advantages and can be used as an important supplement to mainstreaming monolayer GHEs.

High-power actively Q-switched Ho-doped gadolinium tantalate laser.

In this paper, we present the acousto-optical (AO) Q-switched performance of a holmium (Ho):gadolinium tantalate (GdTaO4) (Ho:GTO) laser pumped by a thulium (Tm)-fiber laser emitting at 1.94 µm. In the efficient continuous wave (CW) regime, a maximum output power of 30.5 W at 2068.8 nm was achieved, corresponding to a slope efficiency of 74.9% with respect to the absorbed pump power. In the Q-switching regime, pulse energies of 2.4 mJ, 1.2 mJ, and 0.9 mJ were obtained with pulse repetition frequencies of 10 kHz, 20 kHz, and 30 kHz, respectively. The minimum pulse widths were 18 ns, 23 ns, and 26 ns, corresponding to peak powers of approximately 133.3 kW, 52.2 kW, and 34.6 kW, respectively.

161 W middle infrared ZnGeP2 MOPA system pumped by 300 W-class Ho:YAG MOPA system.

We demonstrated a high-power Q-switched two-stage Ho:YAG master-oscillator power-amplifier (MOPA) system dual-end pumped by Tm:YLF lasers. A new method was introduced by rotating and swapping spatial axial directions of pump beams to improve the beam quality of the Ho:YAG oscillator and first-stage amplifier. Two parallel second-stage Ho:YAG amplifiers were employed to output high power. A total maximum average output power of 332 W at 2091 nm with pulse repetition frequency of 20 kHz was achieved. Then a ZnGeP2 MOPA system was demonstrated using the Ho:YAG MOPA as the pump source. A maximum average output power of 161 W at 3-5 µm was obtained with 290 W incident Ho pump power, corresponding to beam quality factors M2 of 3.42 and 3.83 for horizontal and vertical directions, respectively.

Continuously tunable high-power single-longitudinal-mode Ho:YLF laser around the P12 CO2 absorption line.

A continuously tuned single-longitudinal-mode (SLM) Ho:YLF laser around the P12 CO2 absorption line was demonstrated. The continuous tuning range of 5.75 pm within one longitudinal mode spacing of the Ho:YLF resonator was realized by using a novel intra-cavity wedge prism device fixed on the piezoelectric transducer (PZT) as the cavity length controller. High SLM power of 11.3 W was obtained from a Ho:YLF amplifier with three crystals at the pump power of 31.8 W and master oscillator power of 323 mW, corresponding to a gain of 15.44 dB and an optical-to-optical conversion efficiency of 34.5%. The beam quality factors M2 of the SLM Ho:YLF amplifier in the x and y directions were estimated to be 1.04 and 1.05, respectively.

Research on performance improvement technology of a BaGa4Se7 mid-infrared optical parametric oscillator.

In this Letter, we demonstrate an average output power of 5.12 W at 3-5 µm from a type-I phase-matching BaGa4Se7 (BGSe) optical parametric oscillator (OPO), which is pumped by a 2090 nm Q-switched Ho:YAG laser with pulse repetition frequency of 1 kHz. At maximum output level, the corresponding slope efficiency and optical-to-optical conversion efficiency are 30.0% and 18.3%, respectively. Moreover, under ring cavity conditions, the BGSe OPO produced a 3.04 W mid-infrared laser with high beam quality factors M2 of 1.47 in the horizontal direction and 1.51 in the vertical direction. Besides, the wavelength-tuning curve for type-I BGSe was also investigated, corresponding to an idler wavelength-tuning range of 4.5-5.3 µm, and the signal light wavelength was 4.5 to 4.1 µm.

Ultrasensitive Magnetic Sensors Enabled by Heterogeneous Integration of Graphene Hall Elements and Silicon Processing Circuits.

Graphene Hall elements (GHEs) have been demonstrated to be promising magnetic field sensors with excellent sensitivity, linearity, temperature stability, and compatibility with complementary-metal-oxide-semiconductor (CMOS)-integrated circuits (ICs). However, the demonstrated GHEs have still not exhibited a comprehensive advantage in performance over commercial integrated Hall sensors which were implemented in integrated Hall element and CMOS processing ICs. In this work, we develop a technology for the three-dimensional (3D) heterogeneous integration of silicon-based CMOS ICs and GHEs, and the fabricated magnetic field sensors outperform commercial high-end integrated Hall sensors. Specifically, the integrated Hall sensors are implemented in a stacked integration on Si based on a chopper programmable-gain amplifier (CPGA), a chopper-stabilized second-order sigma-delta modulator (CSDM), and graphene-based Hall elements on monochips. GHEs with high sensitivity (up to 1000 A/VT) are fabricated with a compatible process on a smoothened silicon nitride passivation layer of silicon-based CMOS ICs, and the two device layers are connected by an interlayer. The heterogeneous integrated Hall ICs exhibit current and voltage magnetic sensitivities up to 64 000 A/VT and 6.12 V/VT, respectively, which are much higher than those in all other reported nanomaterial-based Hall sensors and even in high-end commercial Hall ICs. Furthermore, the 3D heterogeneous integration technology used here can be extended as a universal technology for integrating nanomaterial-based sensors and Si CMOS ICs.

570†MHz harmonic mode-locking in an all polarization-maintaining Ho-doped fiber laser.

In this paper, we demonstrate a 570.0 MHz harmonically mode-locked all-polarization-maintaining Ho-doped fiber laser based on semiconductor saturable absorbed mirror. Firstly, the laser operates in the 15.4 MHz fundamental mode-locked soliton regime, emitting 2051.5 nm, 1.62 ps soliton pulse without Kelly sidebands. And then, the stable 37th-order harmonic mode-locked soliton with maximum repetition rate up to 570.0 MHz at 2053nm is generated. Moreover, colorful soliton rain behaviors are also discussed.

Tunable twisted-mode Ho:YAG laser at continuous-wave and pulsed operation.

A single-longitudinal-mode Ho:YAG laser with a twisted-mode cavity under the continuous-wave and pulsed operation was demonstrated. The maximum continuous-wave single-longitudinal-mode output power of 0.76 W was obtained at the wavelength of 2097.46 nm, corresponding to a slope efficiency of 28.9%. The output wavelength was tuned from 2096.94 nm to 2098.48 nm by utilizing a 0.5-mm-thick etalon. Furthermore, the single-frequency pulsed operation of the twisted-mode Ho:YAG laser was realized by the electro-optic switch. For the 2 kHz pulse repetition frequency, the single-frequency pulse energy reached 0.2 mJ with the pulse width of 116.5 ns. The beam quality factors M2 of the pulsed twisted-mode Ho:YAG laser in the x and y directions were 1.15 and 1.10, respectively.

High-beam-quality 2.1 µm pumped mid-infrared type-II phase-matching BaGa4Se7 optical parametric oscillator with a ZnGeP2 amplifier.

We firstly demonstrated a tunable 2.1 µm pumped mid-infrared type-II phase-matching BaGa4Se7 (BGSe) optical parametric oscillator (OPO). A signal tuning range of 3.82-3.99 µm was achieved. With a signal light produced by the BGSe OPO serving as seed, the ZnGeP2 (ZGP) optical parametric amplifier (OPA) was first introduced. A 4.35 W mid-infrared laser was obtained in the novel type-II BGSe OPO with a ZGP OPA system, which was pumped by a 24 W 1 kHz Q-switched Ho:YAG laser. The beam quality factor M2 of the whole system is ∼2.3, which is over a 50% promotion on the previous M2 results of single BGSe OPO.

Broadband second-harmonic and sum-frequency generation with a long-wave infrared laser in AgGaGe5Se12.

Using an 8 µm long-wave infrared laser as the fundamental wave, we achieved second-harmonic generation (SHG) and sum-frequency generation simultaneously in AgGaGe5Se12 and obtained a 4 µm laser output. Among them, SHG was achieved in the 173 nm spectral range of the fundamental wave, which was consistent with theoretical calculations. The average power of the obtained 4 µm laser was 41 mW, corresponding to an optical-to-optical conversion efficiency of 3.2%. The measured temperature acceptance bandwidth (LδT) (FWHM) was 50 K·cm; the angular acceptance bandwidth (Lδθ) (FWHM) was 13.3 mrad·cm; and the average absorption coefficient in the wavelength range of 0.86-11.30 µm was 0.07cm-1. In addition, the spectral acceptance bandwidth (Lδλ) of fundamental wave in AgGaGe5Se12 SHG and the spectral gain bandwidth of frequency downconversion in AgGaGe5Se12 were calculated. In view of the small absorption coefficient, the large temperature acceptance bandwidth, and the large spectral gain bandwidth, we conclude that AgGaGe5Se12 is a suitable nonlinear crystal for high-power short/mid/long-wave infrared lasers and frequency conversions of nanosecond-femtosecond infrared lasers. These results are conducive to the further development of AgGaGe5Se12 lasers.

11 µm, high beam quality idler-resonant CdSe optical parametric oscillator with continuous-wave injection-seeded at 2.58 µm.

We report an idler-resonant, continuous-wave (CW) seed injected, optical parametric oscillator (OPO) based on cadmium selenide (CdSe). The CdSe OPO was pumped by a 2.09 µm ns-pulsed laser and injection-seeded by a 2.58 µm CW laser. The idler-resonant oscillator was designed to maximize the optical-to-optical conversion efficiency and optimize the beam quality. The injected seed laser was designed to reduce the pump threshold. With this setup, the average idler output power of 802 mW was obtained corresponding to a pulse energy of 0.8 mJ at the wavelength of 11.01 µm and linewidth (FWHM) of 0.6 cm-1, optical-to-optical conversion efficiency of 4.4%, quantum conversion efficiency of 23.3%, beam quality of M2x = 1.23, M2y = 1.12, and pulse width of 21 ns. In addition, by turning the angle of the CdSe, wavelength tuning of 10.55-11.98 µm was achieved.

1 W, 10.1 µm, CdSe optical parametric oscillator with continuous-wave seed injection.

We demonstrated a 2.1 µm nanosecond laser pumped, 2.6 µm continuous-wave (CW) seed injected, cadmium selenide (CdSe) signal singly resonant optical parametric oscillator (OPO). A maximum average power of 1.05 W was obtained corresponding to a pulse energy of 1.05 mJ at the idler wavelength of 10.1 µm and optical-to-optical conversion efficiency of 4.69%, beam quality of $M_x^2={2.25}$Mx2=2.25, $M_y^2={2.12}$My2=2.12 and pulse width of 24.4 ns. To the best of our knowledge, this is the first time to achieve 10-12 µm laser with watt-level average power using OPO technology.

3.5 W long-wave infrared ZnGeP2 optical parametric oscillator at 9.8 µm.

We demonstrated a high-power long-wave infrared optical parametric oscillator at 9.8 µm based on a type-I phase-matching ${{\rm ZnGeP}_2}$ZnGeP2 crystal. By using a ${Q}$Q-switched 2091 nm Ho:YAG laser with pulse repetition frequency of 10 kHz as the pump source, the maximum average output power of 3.51 W at 9.8 µm was achieved with incident pump power of 90 W, corresponding to a slope efficiency of 4.81% and conversion efficiency at maximum pump power of 3.9%. The pulse width of 19.6 ns and linewidth of 142 nm were obtained at maximum output level. In addition, the beam quality factor ${M^2}$M2 was measured to be ${\sim}{2.2}$∼2.2.

Single-longitudinal-mode Ho:YVO4 MOPA system with a passively Q-switched unidirectional ring oscillator.

A 2052.96 nm single-longitudinal-mode pulsed Ho:YVO4 MOPA system was demonstrated for the first time. The pulsed Ho:YVO4 MOPA system consisted of a unidirectional ring passively Q-switched oscillator and a single-pass amplifier. By inserting an isolator, a half-wave plate and a Cr2+:ZnS plate into the ring Ho:YVO4 oscillator cavity, the single-longitudinal-mode pulsed laser was achieved with an average output power of 1.02 W with pulse width of 910 ns and pulse repetition frequency (PRF) of 67 kHz. Using the residual (non-absorbed) pump power of the oscillator as pump, the single-pass pulsed Ho:YVO4 amplifier obtained an average output power of 1.67 W. The total optical-to-optical efficiency of the pulsed Ho:YVO4 MOPA system was 14.3%. Single-longitudinal-mode pulsed MOPA system based on isolator and Cr2+:ZnS around 2 µm has not been reported yet to the best of our knowledge.

High efficiency single-longitudinal-mode resonantly-pumped Ho:GdTaO4 laser at 2068nm.

Based on Faraday effect we demonstrate a thulium fiber pumped continuous-wave single-longitudinal-mode laser with a new Ho:GdTaO4 crystal. By inserting a faraday rotator and a half-wave plate into the laser cavity, the single-longitudinal-mode output power of 392 mW at wavelength of 2068.33 nm was obtained in unidirectional Ho:GdTaO4 ring laser, corresponding to a slope efficiency of 60.2% respect to the absorbed pump power. Furthermore, utilizing the Ho:GdTaO4 power amplifier, the maximum single-longitudinal- mode output power of 1.02 W was achieved.