Vertical External Cavity Surface Research Articles

Twisted-mode VECSEL with intracavity second harmonic generation.

A vertical external cavity surface emitting laser (VECSEL) that uses intracavity second harmonic generation (SHG) and the twisted mode technique for power scaling was explored. The effects of the twisted mode technique are shown and discussed by examining the mode structure and spectrum of the fundamental mode. The maximum SHG output was 1 W at 458 nm while the fundamental was lasing in the TEM00 mode. We conclude that the twisted mode technique does not interfere with intracavity SHG and is a reasonable path for power scaling intracavity frequency doubled VECSELs.

Infrared vertical external cavity surface emitting laser threshold magnetometer

Nitrogen-vacancy (NV) centers have considerable promise as high sensitivity magnetometers; however, they are commonly limited by inefficient collection and low contrasts. Laser threshold magnetometry (LTM) enables efficient collection and high contrasts, providing a path toward higher sensitivity magnetometry. We demonstrate an infrared LTM using an ensemble of NV centers in a single-crystal diamond plate integrated into a vertical external cavity surface emitting laser. The laser was tuned to the spin-dependent absorption line of the NV centers, allowing for optical readout by monitoring the laser output power. We demonstrate a magnetic sensitivity of 7.5 nT/Hz in the frequency range between 10 and 50 Hz. Furthermore, the contrast and the projected photon shot noise limited (PSNL) sensitivity are shown to improve significantly by operating close to the lasing threshold, achieving 18.4% and 26.6 pT/Hz near the threshold. In addition, an unexpected saturable absorption phenomenon was observed near the threshold, which enhanced the contrast and projected PSNL sensitivity.

Investigation of noise correlations in the phase-locked class-A VECSEL array

We theoretically and experimentally study the noise correlations in an array of lasers based on a VECSEL (Vertical External Cavity Surface Emitting Laser) architecture. The array of two or three lasers is created inside a planar degenerate cavity with a mask placed in a self-imaging position. Injection from each laser to its neighbors is created by diffraction, which creates a controllable complex coupling coefficient. The noise correlations between the different modes are observed to be dramatically different when the lasers are phase-locked or unlocked. These results are well explained by a rate equation model that takes into account the class-A dynamics of the lasers. This model permits the isolatation of the influence of the complex coupling coefficients and of the Henry α-factor on the noise behavior of the laser array.

High output power, single mode, and TEM00 operation of a multiple gain chip VECSEL using a twisted-mode configuration.

A vertical external cavity surface emitting laser (VECSEL) has been developed for a sodium guide star application. Stable single frequency operation with 21 W of output power near 1178 nm with multiple gain elements while lasing in the TEM00 mode has been achieved. Higher output power results in multimode lasing. For the sodium guide star application, the 1178 nm can be frequency doubled to 589 nm. The power scaling approach used involves using multiple gain mirrors in a folded standing wave cavity. This is the first demonstration of a high power single frequency VECSEL using a twisted-mode configuration and multiple gain mirrors located at the cavity folds.

Intra-Cavity Astigmatic Mode Converting VECSEL

We report the design and demonstration of a vertical external cavity surface emitting laser with intra-cavity astigmatic mode converters. Using a flexible optical pumping scheme Hermite-Gaussian transverse modes were excited at the gain chip and end mirror, and Laguerre-Gaussian transverse modes were observed between the two astigmatic mode converters. Adjusting the flexible pumping scheme allowed for mode order tuning while the laser was operating.

MOCVD growth and thermal stability analysis of 1.2 µm InGaAs/GaAs multi quantum well structure

InGaAs/GaAs multiple quantum well (MQW) is desirable for many optoelectronic devices with the wavelength around 1.2 µm. However, the high defect density and instability caused by high strain have always been the problems. In this paper, an InGaAs/GaAs MQW structure was grown on GaAs substrate at low temperature by metal-organic chemical vapor deposition (MOCVD) technology. The InGaAs layers were grown with triethylgallium (TEGa) and trimethylgallium (TMGa), respectively. We studied the stability of InGaAs/GaAs MQW by evaluating the photoluminescence (PL) peak shift after annealing. It was found that the peaks of MQW grown by TEGa and TMGa were both blue-shifted after annealing. A smaller shift (<4 nm) in the MQW grown with TEGa exhibits better thermal stability compared to that of MQW grown with TMGa. This could be due to the weaker indium (In) and gallium (Ga) interdiffusion at the InGaAs/GaAs interface for the sample grown with TEGa. Furthermore, we fabricated a vertical external cavity surface emitting laser (VECSEL) based on the 6-period InGaAs/GaAs MQW grown with TEGa with an emission wavelength of ~1.2 µm.

Effect of linewidth enhancement factor on the generation of optical vortices in a class-A degenerate cavity semiconductor laser.

The dynamical behavior of a one-dimensional ring array of lasers generated in a class-A degenerate cavity semiconductor laser is numerically investigated. The class-A behavior of the laser is obtained by considering a low-loss vertical external cavity surface emitting laser (VECSEL), in which a telescope and a mask allow us to control the geometry and the linear nearest-neighbour coupling between the lasers. The behavior of the lasers is simulated using coupled rate equations, taking the influence of the Henry factor into account. It is shown that the ring array of lasers exhibits multistability. Moreover, by comparison with a class-B semiconductor laser, it is proved that the class-A nature of the laser makes it more robust to the increase of the Henry factor when it comes to generating topological charge carrying arrays of lasers, thus opening new perspectives of application for such lasers.

324-fs Pulses From a SESAM Modelocked Backside-Cooled 2-μm VECSEL

We present the first modelocked backside-cooled GaSb VECSEL (Vertical External Cavity Surface Emitting Laser) operating above <inline-formula> <tex-math notation="LaTeX">$2 ~\mu \text{m}$ </tex-math></inline-formula>. Using a two quantum well InGaSb SESAM (SEmiconductor Saturable Absorber Mirror) in a V-shaped cavity arrangement we obtain femtosecond modelocking at a center wavelength of 2061 nm, with pulses as short as 324 fs, an average output power as high as 65 mW at a repetition rate of 3 GHz. An operation in a picosecond regime is further demonstrated with an even higher average output power of up to 260 mW and 4.5-ps pulses. We perform a characterization in both the femto- and picosecond regimes with measurements of the pulse duration, the optical spectrum, and the pulse repetition rate (frequency and time domain analysis) at low and high power. In this context, the influence of intracavity group delay dispersion (GDD) is investigated. We find that GDD has a strong influence on the pulse duration (fs or ps regime) and thus on the performance of our SESAM-modelocked 2-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> GaSb VECSEL.

Dual-wavelength Emission of Vertical External Cavity Surface Emitting Laser with Single Gain Chip

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High average output power from a backside-cooled 2-µm InGaSb VECSEL with full gain characterization.

We compare the gain and continuous wave lasing properties of two InGaSb-based vertical external cavity surface emitting lasers (InGaSb VECSEL) with different heat management approaches operating at a center wavelength of around 2μ m. To date, intracavity heatspreaders have been required for good average output power, which have many trade-offs, especially for passive modelocking. Here we demonstrate a record high average output power of 810 mW without an intracavity heatspreader using a backside-cooled non-resonant VECSEL chip optimized for modelocking. In addition, we introduce and demonstrate an optical characterization for a wavelength range of 1.9 to 3μ m to precisely measure wavelength-dependent gain saturation and spectral gain. Gain characteristics are measured as a function of wavelength, fluence, pump power and temperature. Small signal gain of more than 5%, small saturation fluences and broad gain bandwidths of more than 90 nm are demonstrated. In comparison to a commercial VECSEL chip with an intracavity heatspreader, we have obtained similar average output power even though our VECSEL chip is designed for antiresonance.

Accurate [formula omitted]NH[formula omitted] line-list for the 2.3 [formula omitted]m spectral region

The narrow linewidth Vertical External Cavity Surface Emitting Laser (VECSEL) was used to record the high-resolution ammonia spectra in the 2.3 μm atmospheric transparency window at temperatures from 160 to 296 K. In the 4275-4356 cm−1 (∼ 2295-2339 nm) range 807 transitions were identified as belonging to the 14NH3, extending our previous room temperature study of 340 transitions. The temperature dependence of line absorbance was used to retrieve the lower state energy for 682 transitions. By comparing the variationally computed line list and exploiting the lower state combination differences relations, the quantum assignment was proposed for 703 lines representing over 99.9% of integrated 14NH3 absorption in the range. These transitions reached 611 different upper state levels belonging to 23 vibrational bands. For 340 of them, their experimental energy value was retrieved for the first time. The comparison of our line list to the HITRAN2016 and HITRAN2020 is presented and discussed.

All-intracavity fourth harmonic generation in a passively mode locked VECSEL for ultrafast UV emission

We demonstrate all-intracavity fourth harmonic generation in an ultrafast passively mode locked vertical external cavity surface emitting laser (VECSEL). This novel laser cavity design utilizes a high Q Z-cavity resonator to buildup the circulating power of the second harmonic for frequency quadrupling the fundamental 1060 nm to 265 nm. The demonstrated UV output has an average power of 525 μW, pulse width of 3 ps, and a repetition rate of 510 MHz. This results in a peak pulse power of 250–300 mW over a 30 min duration without active stabilization equipment.

Electrically pumped shot-noise limited class A VECSEL at telecom wavelength.

Class A shot-noise limited operation is achieved in an electrically pumped vertical external cavity surface emitting laser (VECSEL), opening the way for integration of such peculiar noiseless laser oscillation in applications where low power consumption and footprint are mandatory. The quantum well active medium is grown on an InP substrate to enable laser oscillation at telecom wavelengths. Single frequency class A operation is obtained by proper optimization of the cavity dimensions, ensuring at the same time a sufficiently long and high-finesse cavity without any intracavity filtering components. The laser design constraints due to electrical pumping are discussed as compared to optical pumping. The intensity noise spectrum of this laser is shown to be shot-noise limited, leading to a relative intensity noise of $-160\;{\rm dB/Hz}$ for 3.1 mA detected photocurrent.

VECSEL-based virtually imaged phased array spectrometer for rapid gas phase detection in the mid-infrared.

We present a novel, to the best of our knowledge, system for high-resolution, time-resolved spectroscopy in the mid-wave infrared based on a modelocked vertical external cavity surface emitting laser (VECSEL) frequency comb coupled to a virtually imaged phased array (VIPA) spectrometer. The GHz level repetition rate of VECSEL-based systems coupled to VIPA spectrometers enables comb tooth resolved spectra without the use of additional filter cavities often required to increase comb tooth spacing. We demonstrate absorption spectroscopy on a methane (CH4) gas mixture at 2900cm-1 (3.4 µm) with over 35cm-1 spectral bandwidth in a single image. Rapid time-resolved measurements were made using a 300 µs exposure time with an acquisition rate limited to 125 Hz by the available camera. High-resolution absolute frequency measurements were performed by scanning the repetition rate of the VECSEL frequency comb.

High peak power, sub-ps green emission in a passively mode locked W-cavity VECSEL.

We report on the experimental results of a passively mode-locked vertical external cavity surface emitting laser (VECSEL), implemented in a W-cavity configuration, using a lithium triborate (LBO) crystal for intra-cavity second harmonic generation (SHG) at 528 nm. The W-cavity configuration allows separation of the crystal from the semiconductor saturable absorber mirror (SESAM), enabling independent control over the Gaussian beam sizes at the crystal, chip, and SESAM. This optimized cavity demonstrated a second harmonic pulse width of ~760 fs at a frequency of 465 MHz and 230 mW average output power, resulting in a peak pulse power of 580 W.

Single crystal diamond gain mirrors for high performance vertical external cavity surface emitting lasers

We report on the design, fabrication and optical performance of gain mirrors in single crystal diamond substrates for vertical external cavity surface emitting lasers (VECSELs). VECSELs have gained attention recently due to their potential for high emission power in single mode with low beam divergence, yet their maximum output power remains typically limited due to thermal roll-over resulting from insufficient heat dissipation. In order to increase the heat transfer, we exploit the excellent thermal conductivity of single crystal diamond, which is assembled in direct contact with the active structure. The optical cavity is hereby defined by an output coupler and a high reflection grating structure etched into the diamond surface. We here present the design and microfabrication of a diffraction grating that was optimized to reflect light into the 0th order, therefore combining the role of a gain mirror and a heatsink at the same time. Our process involved metal mask deposition onto the diamond surface, e-beam lithography and reactive ion etching. Characterization showed reflection above 95% at a center wavelength of 1550 nm, potentially allowing the integration of the diamond mirror into a vertical external cavity surface emitting laser.

Design of gain region of high-power vertical external cavity surface emitting semiconductor laser and its fabrication

&lt;sec&gt; The vertical external cavity surface emitting laser (VECSEL) is one of the hottest research fields of semiconductor lasers, due to its high power and good beam quality. However, there are few reports about how to systematically design the active region of VECSEL. In this paper, the gain design of quantum wells, which are the most important region within the VECSEL, is carried out. &lt;/sec&gt;&lt;sec&gt; To achieve low power consumption under high temperature condition, epitaxial structure of the VECSEL is optimized by using the commercial software PICS3D. Firstly, the relationship between the structure of quantum well and the gain is simulated by the &lt;i&gt;k&lt;/i&gt;·&lt;i&gt;p&lt;/i&gt; method. Then, the gain spectra of quantum wells at different carrier densities and temperatures are compared with each other, and the optimal composition and thickness of quantum well are thus determined. The temperature drift coefficient is 0.36 nm/K, obtained by simulating the drift of the gain peak wavelength at the working temperature. Finally, the gain spectra of quantum wells with five different barriers are compared with each other. The slight blue shift of the gain peak in the quantum well with five different barriers accommodates the different emission thermal drifts of the quantum well at high temperature operation. With the GaAsP barriers on both sides of quantum well the gain characteristics of quantum wells can be improved efficiently. &lt;/sec&gt;&lt;sec&gt; The designed structure is deposited by the MOCVD system. According to the reflection spectrum of the gain chip, measured by ellipsometer, the stop-band over 100 nm is centered at the about 970 nm wavelength, confirming accurate growth of the VECSEL. The 808 nm pump laser is focused on the surface of VECSEL chip at an incident angle from 30° to 50°. The VECSEL light-light characteristics are tested under the output coupling mirror with different reflectivity. The output power of VECSEL with a 97.7% reflectance output coupling mirror reaches 9.82 W at the pumping power of 35 W, without saturating the power curve. By using the external mirrors with different reflectivity, there appears the wavelength shift with the pumping power changing from 0.216 nm/W to 0.16 nm/W. Thus, the internal heating effects are different for VECSEL with different mirrors. The divergence angles at two orthogonal directions are 9.2° and 9.0°, respectively. And the circle profile of optical field shows good symmetry. &lt;/sec&gt;

Several New Semiconductor Lasers and Status, Challenges and Insights of Related Industries

As the basis of the whole laser industry, the semiconductor laser industry is not only large-scaled but also has strong radiation and driving capacities. The semiconductor lasers are widely used in industrial, military, and living consumption fields such as optical communication, optical information processing, novel manufacturing, laser display, and biological and medical sensing. To adapt to the gradually expanding application range and satisfy the new requirements of different application scenarios, various new mechanisms, concepts, and structures have been introduced into the semiconductor laser industry through interdisciplinary penetration, greatly optimizing the wavelength coverage, beam quality, device volume, power consumption, modulation speed, and output power of the semiconductor lasers. This paper introduces several rapidly developed new semiconductor lasers by comparing their physical connotation, structural design, and preparation methods. Considering the current development status of related industries in China, we suggest that the development of the semiconductor laser industry should be closely combined with industrial application. The performance of the semiconductor lasers should be optimized in a closed-loop manner relying on the market capacity and the strong systematic development ability in China to promote the key technologies. New principles, structures, and processes should be continually introduced into this industry through interdisciplinary integration. Meanwhile, using the policy-oriented advantages in China, we suggest to increase investment in vertical external cavity surface emitting lasers, micro-nano lasers, and topological insulator lasers and conduct mass production and controllable production, thus to seize the leading position in international competition in the related fields.

High-Power Higher Order Hermite–Gaussian and Laguerre–Gaussian Beams From Vertical External Cavity Surface Emitting Lasers

We report a vertical external cavity surface emitting laser (VECSEL) with an optical pumping scheme for the generation of higher order Hermite–Gaussian transverse modes. The VECSEL chip with emission around 1068 nm in a linear cavity configuration is capable of delivering a variety of higher order modes with Watt-level output power. A very good agreement between the modeling and experimental results validate the ideas underpinning the method. Additionally, simultaneous lasing of two independent and collinear transverse modes from a single laser cavity is demonstrated. An external astigmatic mode converter is finally utilized for the conversion of Hermite–Gaussian modes into corresponding Laguerre–Gaussian modes.

Flip-Chip Wafer-Fused OP-VECSELs Emitting 3.65 W at the 1.55-μm Waveband

Optically pumped vertical external cavity surface emitting lasers (VECSELs) based on flip-chip gain mirrors emitting at the 1.55 μm wavelength range are reported. The gain mirrors employ wafer-fused InAlGaAs/InP quantum well heterostructures and GaAs/AlAs distributed Bragg reflectors fixed on a diamond heat-sink substrate in a flip-chip geometry, incorporated in a V-cavity configuration. A maximum output power of 3.65 W was achieved for a heatsink temperature of 11°C and employing a 2.2% output coupler. The laser exhibited circular beam profiles for the full emission power range. This demonstration represents more than five-fold increase of the output power compared to the state-of-the-art flip-chip VECSELs previously reported at the 1.55 μm wavelength range. It opens new perspectives for developing practical VECSEL-based laser systems operating at a wavelength range widely used in many applications.