Room-temperature Laser Operation Research Articles

Broadly tunable continuous-wave Tm,Ho:SrF2 and Tm,Ho:BaF2 lasers

We report on the first, to our knowledge, room-temperature continuous-wave laser operation of Tm3+,Ho3+-codoped barium and strontium fluoride crystals at ∼2.1 µm. The 3 at.% Tm, 0.5 at.% Ho:BaF2 laser generated 160 mW at 2073 nm with a slope efficiency of 31.0% and a laser threshold of 43 mW. The continuous wavelength tuning of this laser from 2010 to 2090 nm (tuning range, 80 nm) was demonstrated. The spectroscopic properties of Tm,Ho:SrF2 and Tm,Ho:BaF2 crystals were also determined, showing enhanced Tm3+ → Ho3+ energy transfer in rare-earth clusters. For Ho3+ ions in BaF2, the stimulated-emission cross section is 0.40 × 10−20 cm2 at 2044 nm, and the thermal equilibrium luminescence lifetime is as long as 14.1 ms.

Room‐temperature laser operation of a (Ga,In)As/Ga(As,Bi)/(Ga,In)As W‐type laser diode

The ongoing pursuit for laser device emitting in the near-infrared spectral region on GaAs substrates has led to various material systems and device concepts. Alloys containing dilute amounts of Bismuth are promising candidates due to the already substantial band gap shift when incorporating low molar fractions of Bi in the GaAs host lattice. However, devices emitting at technologically essential wavelengths of 1.3 and 1.55 μm have yet to be demonstrated using this material system. Especially the non-equilibrium nature of the growth conditions required to grow the metastable material makes epitaxial growth with high molar fractions of Bi challenging. An alternate approach to reach the desired wavelengths exploits a type-II band alignment between two materials to push the emission wavelength further into the telecom bands. Here, room-temperature laser operation of the first type-II structure employing Ga(As,Bi) as hole confining layer and (Ga,In)As as electron confining layer is demonstrated. Sample growth is conducted by low-pressure metalorganic vapour phase epitaxy. Broad area laser devices are processed and characterized by electroluminescence measurements. A threshold current density of 3.86 kA/cm2 and emission wavelength of 1037 nm are observed, showing this device concept's potential for future lasers in the telecom bands.

Ultralow-Threshold Continuous-Wave Room-Temperature Crystal-Fiber/Nanoperovskite Hybrid Lasers for All-Optical Photonic Integration.

Continuous-wave (CW) room-temperature (RT) laser operation with low energy consumption is an ultimate goal for electrically driven lasers. A monolithically integrated perovskite laser in a chip-level fiber scheme is ideal. However, because of the well-recognized air and thermal instabilities of perovskites, laser action in a perovskite has mostly been limited to either pulsed or cryogenic-temperature operations. Most CW laser operations at RT have had poor durability. Here, crystal fibers that have robust and high-heat-load nature are shown to be the key to enabling the first demonstration of ultralow-threshold CW RT laser action in a compact, monolithic, and inexpensive crystal fiber/nanoperovskite hybrid architecture that is directly pumped with a 405 nm diode laser. Purcell-enhanced light-matter coupling between the atomically smooth fiber microcavity and the perovskite nanocrystallites gain medium enables a high Q (≈1500) and a high β (0.31). This 762 nm laser outperforms previously reported structures with a record-low threshold of 132nW and an optical-to-optical slope conversion efficiency of 2.93%, and it delivers a stable output for CW and RT operation. These results represent a significant advancement toward monolithic all-optical integration.

Room-temperature continuous-wave operation of green vertical-cavity surface-emitting lasers with a curved mirror fabricated on {20−21} semi-polar GaN

We demonstrate a room-temperature continuous-wave operation of green vertical-cavity surface-emitting laser (VCSEL) with a 20 μm long cavity possessing a dielectric curved mirror formed over a {20−21} semi-polar gallium nitride substrate. The emission wavelength and the threshold current were 515 nm and 1.8 mA, respectively. We also confirmed that white light is generated by overlaying three prime colors of light, i.e. red, blue and green, emitted only from VCSEL.

Fabrication of Er:Y2O3 transparent ceramics for 2.7 μm mid-infrared solid-state lasers

Laser grade 7 at.% Er:Y2O3 transparent ceramics with submicron grain size were fabricated by using one-step vacuum sintering followed by hot isostatic pressing (HIPing) technique. Through studying the sintering trajectory of Er:Y2O3 ceramics, the sintering temperature zone where sufficient relative density (>96%), no pore-boundary separation, and sub-micron grain size (<1 μm) ceramic samples could be identified. The samples pre-sintered in this zone were readily densified by HIPing. To maximum the densification and achieve high transparency, it is critical to suppress the final-stage grain growth. After HIPing at 1520 °C, the Er:Y2O3 ceramics were fully densified without further grain growth, and exhibited in-line transmission of about 81.6% at 2000 nm. Continuous wave (CW) room temperature laser operation of the Er:Y2O3 transparent ceramic at 2.7 μm was demonstrated.

Design of AlGaN-based lasers with a buried tunnel junction for sub-300 nm emission

This paper discusses the design of electrically-pumped AlGaN-based in-plane lasers emitting at ∼290 nm. Our laser design utilizes strained Al0.5Ga0.5N quantum wells, and a novel polarization engineered AlGaN/InGaN/AlGaN-based tunnel junction. The low ­resistive tunnel junction is used as an intracavity contact in the device in place of the resistive p-type contact; which leads to improved hole injection and a reduced threshold voltage. Hence, room-temperature continuous-wave laser operation could be enabled. Strategies to improve the performance of the tunnel junction contact through the incorporation of low concentrations of boron in the highly-doped AlGaN tunnel junction layers as a means to increase the polarization sheet charge are also discussed.

Room-temperature continuous-wave lasing from monolayer molybdenum ditelluride integrated with a silicon nanobeam cavity.

Monolayer transition-metal dichalcogenides (TMDs) have the potential to become efficient optical-gain materials for low-energy-consumption nanolasers with the smallest gain media because of strong excitonic emission. However, until now TMD-based lasing has been realized only at low temperatures. Here we demonstrate for the first time a room-temperature laser operation in the infrared region from a monolayer of molybdenum ditelluride on a silicon photonic-crystal cavity. The observation is enabled by the unique combination of a TMD monolayer with an emission wavelength transparent to silicon, and a high-Q cavity of the silicon nanobeam. The laser is pumped by a continuous-wave excitation, with a threshold density of 6.6 W cm-2. Its linewidth is as narrow as 0.202 nm with a corresponding Q of 5,603, the largest value reported for a TMD laser. This demonstration establishes TMDs as practical materials for integrated TMD-silicon nanolasers suitable for silicon-based nanophotonic applications in silicon-transparent wavelengths.

Room-temperature subnanosecond waveguide lasers in Nd:YVO4 Q-switched by phase-change VO2: A comparison with 2D materials

We report on room-temperature subnanosecond waveguide laser operation at 1064 nm in a Nd:YVO4 crystal waveguide through Q-switching of phase-change nanomaterial vanadium dioxide (VO2). The unique feature of VO2 nanomaterial from the insulating to metallic phases offers low-saturation-intensity nonlinear absorptions of light for subnanosecond pulse generation. The low-loss waveguide is fabricated by using the femtosecond laser writing with depressed cladding geometry. Under optical pump at 808 nm, efficient pulsed laser has been achieved in the Nd:YVO4 waveguide, reaching minimum pulse duration of 690 ps and maximum output average power of 66.7 mW. To compare the Q-switched laser performances by VO2 saturable absorber with those based on two-dimensional materials, the 1064-nm laser pulses have been realized in the same waveguide platform with either graphene or transition metal dichalcogenide (in this work, WS2) coated mirror. The results on 2D material Q-switched waveguide lasers have shown that the shortest pulses are with 22-ns duration, whilst the maximum output average powers reach ~161.9 mW. This work shows the obvious difference on the lasing properties based on phase-change material and 2D materials, and suggests potential applications of VO2 as low-cost saturable absorber for subnanosecond laser generation.

Room-temperature terahertz emission from ZnSe-based quantum cascade structures: A simulation study

We identified conditions for room-temperature operation of terahertz quantum cascade lasers (THz QCLs) where variable barrier heights are used on ZnSe/Zn1–xMgx Se material systems. The THz QCL devices are based on three-level two-well design schemes. The THz QCL lasers with alternating quantum barriers with different heights were compared with THz QCL laser structures with fixed quantum barrier heights. It is found that the THz QCL device with novel design employing variable barrier heights achieved the terahertz emission of about 1.45 THz at room-temperature (300 K), and has improved laser performance due to the suppression of thermally activated carrier leakage via higher-energy parasitic levels. Thus, THz QCL devices employing the design with variable barrier heights may lead to future improvements of the operating temperature and performance of THz QCL lasers. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Remote Sensing with Commutable Monolithic Laser and Detector.

The ubiquitous trend toward miniaturized sensing systems demands novel concepts for compact and versatile spectroscopic tools. Conventional optical sensing setups include a light source, an analyte interaction region, and a separate external detector. We present a compact sensor providing room-temperature operation of monolithic surface-active lasers and detectors integrated on the same chip. The differentiation between emitter and detector is eliminated, which enables mutual commutation. Proof-of-principle gas measurements with a limit of detection below 400 ppm are demonstrated. This concept enables a crucial miniaturization of sensing devices.

Room-temperature operation of quantum cascade lasers at a wavelength of 5.8 μm

The room-temperature generation of multiperiod quantum-cascade lasers (QCL) at a wavelength of 5.8 μm in the pulsed mode is demonstrated. The heterostructure of a quantum-cascade laser based on a heterojunction of InGaAs/InAlAs alloys is grown by molecular-beam epitaxy and incorporates 60 identical cascades. The threshold current density of the stripe laser 1.4 mm long and 22 μm wide is ~4.8 kA/cm2 at a temperature of 303 K. The maximum power of the optical-radiation output from one QCL face, recorded by a detector, is 88 mW. The actual optical-power output from one QCL face is no less than 150 mW. The results obtained and possible ways of optimizing the structure of the developed quantum-cascade lasers are discussed.

Room-temperature continuous-wave operation of GaN-based vertical-cavity surface-emitting lasers with n-type conducting AlInN/GaN distributed Bragg reflectors

The room-temperature continuous-wave operation of a 1.5λ-cavity GaN-based vertical-cavity surface-emitting laser with an n-type conducting AlInN/GaN distributed Bragg reflector (DBR) was achieved. A peak reflectivity of over 99.9% was obtained in the n-type conducting AlInN/GaN DBR so that the current was injected through the DBR for the operation. The threshold current was 2.6 mA, corresponding to the threshold current density of 5.2 kA/cm2, and the operating voltage was 4.7 V. A lasing spectrum with a peak wavelength of 405.1 nm and a full-width at half maximum of 0.08 nm was also observed.

Threshold current reduction and directional emission of deformed microdisk lasers via spatially selective electrical pumping

We report on laser threshold current reduction and directional emission from quadrupole-shaped AlGaInAs microdisk diode lasers by selective electrical pumping. The directional emission results from breaking the 2-fold rotation symmetry of the system by the introduction of a triangle-shaped contact geometry, and the laser threshold reduction results from a small current injection area. Room temperature laser operation is achieved in both pulsed and continuous-wave operation for a microdisk radius of 50 μm and deformation constant of ε = 0.09, with optical output power of more than 8 mW and 3 mW, respectively. Under pulsed operation, the minimum measured threshold current for selectively pumped microlasers is 42 mA, significantly lower than the minimum measured threshold current for uniformly pumped microlasers (58 mA) and standard ridge lasers (80 mA) of the same device size and material.

Room-temperature continuous-wave operation of GaN-based vertical-cavity surface-emitting lasers fabricated using epitaxial lateral overgrowth

We have successfully demonstrated the room-temperature continuous-wave operation of GaN-based vertical-cavity surface-emitting lasers (VCSELs) with all-dielectric reflectors, which were fabricated using epitaxial lateral overgrowth. The VCSELs exhibited a threshold current of 8 mA and a threshold voltage of 4.5 V at a lasing wavelength of 446 nm. The maximum output power was 0.9 mW for an 8-µm-diameter current aperture, which was made possible because of the high thermal conductivity of the GaN substrate.

InGaN-LD-Pumped &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;${\rm Pr}^{3+}$&lt;/tex-math&gt;&lt;/inline-formula&gt;: &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;${\rm LiYF}_{4}$&lt;/tex-math&gt;&lt;/inline-formula&gt; Continuous-Wave Laser at 915 nm

We demonstrate the first InGaN-LD-pumped room temperature and continuous-wave laser operation of a Pr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> : LiYF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> 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 M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> beam quality factors measured in x and y dimensions are about 1.07 and 1.04, respectively.

Diode-pumped continuous-wave laser operation of co-doped (Ho,Tm):KLu(WO4)2 monoclinic crystal

We report on room-temperature continuous-wave laser operation at 2.06 µm in co-doped (0.5 at% Ho, 5.0 at% Tm):KLu(WO 4 ) 2 monoclinic crystal pumped at 805 nm by a commercially available AlGaAs diode laser stack. A maximum output power of 93 mW and a slope efficiency of 14.7% with respect to absorbed power were achieved. • We achieved on room-temperature continuous-wave laser operation at 2.06 µm. • We studied laser operation in (0.5 at% Ho,5.0 at% Tm):KLu(WO 4 ) 2 monoclinic crystal • We achieved a maximum output power of 93 mW and a slope efficiency of 14.7%.

In-band pumped Ho^3+:KY_3F_10 2 μm laser

We report the first observation to our knowledge of room-temperature continuous-wave laser operation on the (5)I(7)→(5)I(8) transition of Ho(3+) ions in a KY(3)F(10) single crystal. Using a Tm-doped silica fiber laser operating at 1938 nm as a pump source, a maximum laser power of 1.8 W was obtained at a wavelength of ~2040 nm for 27 W of absorbed pump power with a slope efficiency of 19.1% with respect to absorbed power. At low cavity output coupling, the lasing wavelength shifted to 2060.5 nm. The beam propagation factor (M(2)) was measured to be <1.06 at the maximum output power, confirming fundamental transverse-mode (TEM(00)) operation. Performing a Caird analysis, we determined resonator round-trip losses and intrinsic slope efficiency of 30% and 43.8%, respectively.

Holmium-doped Lu_2O_3, Y_2O_3, and Sc_2O_3 for lasers above 21 μm

Efficient room-temperature laser operation was obtained in the wavelength range from 2117 nm to 2134 nm with Ho:Lu(2)O(3) and Ho:Y(2)O(3) as the active materials. With an FBG-stabilized Tm-doped fiber laser as the pump source, the maximum slope efficiency and output power of the Ho:Y(2)O(3) laser were 63% and 18.8 W, respectively. With Ho:Lu(2)O(3) the respective values were 76% and 25.2 W. With Ho:Sc(2)O(3) as the active material the accessible wavelength range could be expanded to 2158 nm in a diode-pumped setup.

Room‐temperature operation of InAs‐based interband‐cascade‐lasers beyond 6 µm

A report is presented on long wavelength room-temperature operation of InAs-based interband cascade lasers (ICLs) at 6.06 µm. The broad area and ridge waveguide devices operate in pulsed mode up to 25 and 40 °C, respectively, and therewith extend the available room-temperature operation range of ICLs to longer wavelengths.

Room-temperature 3.73 µm GaSb-based type-I quantum-well lasers with quinternary barriers

Room-temperature operation of GaSb-based type-I lasers with emission wavelength of 3.73 µm is reported for the first time. Ridge-waveguide devices with five quantum wells and quinternary barriers for improved hole confinement lase in pulsed operation with a low transparency threshold current density of 676 A cm−2 for infinite stripe width. The presence of additional loss mechanism is observed above 20 °C, changing the characteristic temperature from 38 K to 16 K and limiting the maximum operating temperature to 32 °C.