Optically Pumped Semiconductor Laser Research Articles

Growth, characterization, and efficient laser operation of Czochralski- and micro-pulling-down-grown Yb3+:YScO3 mixed sesquioxides

We report on the growth, spectroscopy and laser operation of Yb3+-doped mixed sesquioxide crystals. Various Yb3+-doped crystals with compositions close to (Y0.5Sc0.5)2O3 have been successfully grown by the Czochralski method and by the micro-pulling down (µ-PD) method. Our spectroscopic investigations reveal broadened stimulated emission and absorption cross-section spectra originating from the structural disorder of the mixed crystals. We find the peak wavelengths to shift by ∼1.6 nm between Y:Sc-ratios of 54:46 and 46:54 and confirm a linear relation of the peak position with the lattice constant of the host composition. In the laser experiments, we obtain highly efficient continuous-wave laser operation under pumping with an optically-pumped semiconductor laser (OPSL) at ∼975 nm, reaching slope efficiencies of up to 89% at optical-to-optical efficiencies exceeding 80% at laser wavelengths between 1037 nm and 1086 nm.

Compactly Efficient CW 3 to 4.5 μm Wavelength Tunable Mid-Infrared Laser in Optically Pumped Semiconductor Laser With Intracavity OPO

An efficient continuous-wave (CW) mid-infrared laser with a tunable wavelength range from 3 to 4.5 μm is demonstrated by using intracavity optical parametric oscillator (ICOPO). An optically pumped semiconductor laser (OPSL) is applied as the parent pumped laser gain medium to eliminate self-modulation effect caused by Nd-doped gain medium with ICOPO for fulfilling true CW emissions. Simultaneously, the OPSL gain chip with flip-chip packaging method can avoid mode hopping resulted from internal heat spreader etalon when strong depletion in ICOPO was achieved. The diode pump criteria of the OPSL is first investigated to prevent thermal roll over. By observing the spectral and temporal dynamics of the parent pumped OPSL with and without OPO operation, the true CW and mode-hop-free quality of the laser is verified. A low diode pump threshold of 2.67 W is obtained for the mid-IR idler emission and a total extracted idler power is 250 mW at a diode pump power of 8 W. Finally, the wavelength tunability is confirmed by adjusting the horizontal location of the multiple channel MgO:PPLN crystal, which indicated the feasibility of practical application in such a compact configuration.

MHz-repetition rate fs-laser-inscribed crystalline waveguide lasers inscribed at 100 mm/s.

We report on fast direct laser inscription of waveguide laser structures in a crystal. For the first time, a 1 MHz-repetition rate fs-laser was utilized for this purpose. We inscribed and characterized more than 100 tracks with different inscription parameters in Yb:CALGO crystals. Waveguide lasing with slope efficiencies of up to 57% at a maximum output power of 3.4 W and more than 55% of optical efficiency was obtained under pumping with an optically pumped semiconductor laser (OPSL), even in waveguides fabricated at record-high inscription velocities of 100 mm/s. Such laser performance is similar to previously reported waveguide lasers inscribed at 1 kHz repetition rate and paves the way toward an industrial fabrication of such waveguides.

Generating High-Order Transverse Patterns in Optically Pumped Semiconductor Lasers

High-order pattern formation in an optically pumped semiconductor laser (OPSL) under a selective pumping with varying spatial overlap between the pump beam and transverse modes is explored. In contrast to transverse pattern generation by off-axis pumped solid-state lasers where the mode order can be flexibly increased, experimental results reveal that the selective pumping fails to realize high-order mode operation in OPSLs when the pump-to-mode size ratio and pump power are insufficiently large. On the other hand, several high-order patterns belonging to the Hermite-Laguerre-Gaussian (HLG) modes are observed when scanning a large-ratio pump beam to specific positions on the gain chip. These HLG modes are experimentally confirmed to mainly originate from the transverse non-uniformity of present OPSL chip, while their structural features cannot be simply correlated with the pump scanning positions. Nevertheless, it is believed that the first-time observation of pure HLG modes under the large-ratio pumping can offer useful insights into the high-order pattern manipulation in OPSLs.

Observation of reflection feedback induced the formation of bright-dark pulse pairs in an optically pumped semiconductor laser.

It is experimentally demonstrated that the tiny reflection feedback can lead the optically pumped semiconductor laser (OPSL) to be operated in a self-mod-locked state with a pulse train of bright-dark pulse pairs. A theoretical model based on the multiple reflections in a phase-locked multi-longitudinal-mode laser is developed to confirm the formation of bright-dark pulse pairs. The present finding can offer an important insight into the temporal dynamics in mode-locked OPSLs.

Efficient OPSL-pumped mode-locked Yb:Lu2O3 laser with 67% optical-to-optical efficiency.

We present a mode-locked Yb:Lu2O3 laser with up to 67% of optical-to-optical efficiency. By utilizing a high brightness optically pumped semiconductor laser (OPSL) as a pump source and using a semiconductor saturable absorber mirror (SESAM) we obtained self-starting mode locking. A pulse duration of 571 fs at 4.73 W of average output power with an optical-to-optical efficiency of 67% was achieved. In a slightly different cavity configuration the pulse duration was reduced to 313 fs at 2.16 W of average output power. In both cases the pulse duration was longer than the Fourier limit and the spectrum supports significantly shorter pulse durations. The laser wavelength is centered at 1034 nm and the repetition rate is 100.76 MHz in both cases. In continuous wave fundamental mode operation the optical-to-optical efficiency was as high as 78% with output powers exceeding 5 W.

Exploring the influence of high order transverse modes on the temporal dynamics in an optically pumped mode-locked semiconductor disk laser.

We quantitatively investigate the influence of high-order transverse modes on the self-mode locking (SML) in an optically pumped semiconductor laser (OPSL) with a nearly hemispherical cavity. A physical aperture is inserted into the cavity to manipulate the excitation of high-order transverse modes. Experimental measurements reveal that the laser is operated in a well-behaved SML state with the existence of the TEM(0,0) mode and the first high-order transverse mode. While more high-order transverse modes are excited, it is found that the pulse train is modulated by more beating frequencies of transverse modes. The temporal behavior becomes the random dynamics when too many high-order transverse modes are excited. We observe that the temporal trace exhibits an intermittent mode-locked state in the absence of high-order transverse modes.

Efficient upconversion-pumped continuous wave Er3+:LiLuF4 lasers

We report on detailed spectroscopic investigations and efficient visible upconversion laser operation of Er3+:LiLuF4. This material allows for efficient resonant excited-state-absorption (ESA) pumping at 974nm. Under spectroscopic conditions without external feedback, ESA at the laser wavelength of 552nm prevails stimulated emission. Under lasing conditions in a resonant cavity, the high intracavity photon density bleaches the ESA at 552nm, allowing for efficient cw laser operation.We obtained the highest output power of any room-temperature crystalline upconversion laser. The laser achieves a cw output power of 774mW at a slope efficiency of 19% with respect to the incident pump power delivered by an optically-pumped semiconductor laser. The absorption efficiency of the pump radiation is estimated to be below 50%.To exploit the high confinement in waveguides for this laser, we employed femtosecond-laser pulses to inscribe a cladding of parallel tracks of modified material into Er3+:LiLuF4 crystals. The core material allows for low-loss waveguiding at pump and laser wavelengths. Under Ti:sapphire pumping at 974nm, the first crystalline upconversion waveguide laser has been realized. We obtained waveguide-laser operation with up to 10mW of output power at 553nm.

Emission properties and CW laser operation of Pr:YLF in the 910 nm spectral range.

The polarized emission spectra for the 3P0→1G4 emission transition of the Pr3+ ion around 910 nm in the Pr3+:LiYF4 (Pr:YLF) laser crystal were registered and calibrated in unit of cross sections for the first time. Continuous-wave (CW) laser operation is demonstrated at 915 nm in π polarization by pumping the crystal with an optically pumped semiconductor laser (OPSL) at 479.2 nm. An output power of 218 mW is thus obtained with a laser slope efficiency of about 24% for an output coupler (OC) transmission of 1.9%. CW laser operation is also demonstrated at 907 nm in σ polarization by using a thin plate oriented at Brewster angle. An output power of about 89 mW with a slope efficiency of about 10% is then obtained for an OC transmission of 0.8%.The round-trip cavity losses are estimated for different experimental cavity configurations to be about 1% and the typical beam quality M2 factors measured in the transverse x and y directions are found equal to about 1.07 and 1.04, respectively. Finally, we also report on a double laser wavelength operation by using an OC with a transmission of about 0.05%, such effect resulting from joint-etalon effects inside the cavity.

Injection-locked operation of an optically pumped semiconductor laser.

We demonstrate a single-frequency, continuous-wave, optically pumped semiconductor laser (OPSL) using an injection-locking technique. Parameters such as output coupling, injection power, and injection wavelength are investigated. With the proper parameters, the output power of the injection-locked laser exceeds the output power of its free-running condition. With 1.5 W of injection power from the master laser, over 9 W of output power is achieved at 1015 nm.

Observation of self-mode-locking assisted by high-order transverse modes in optically pumped semiconductor lasers

The criterion for achieving the self-mode-locking (SML) in an optically pumped semiconductor laser (OPSL) with a linear cavity is systematically explored. Experimental results reveal that the occurrence of SML can be assisted by the existence of high-order transverse modes. Numerical analysis is performed to confirm that the critical pump power for obtaining the SML operation agrees very well with the pump threshold for exciting TEM1,0 mode. The present finding offers an important insight into laser physics and a useful indication for obtaining the SML operation in OPSLs.

High Peak Power From Optically Pumped Mid-IR Semiconductor Lasers

We present work on the high-peak power pumping of optically pumped mid-IR semiconductor lasers. The lasers incorporated 14 type-II InAs/InGaSb/InAs quantum wells (QW). Thick quaternary absorber layers (InGaAsSb) surrounded the QWs, which allowed a large fraction of pump light to be absorbed. The devices were optically pumped with the output of a passively Q-switched Ho:YAG laser at λ = 2.09 μm. The Ho:YAG maximum output power was ~90 kW; this allows the optically pumped semiconductor lasers (OPSLs) to be pumped at several thousand times above threshold. Emission from the QW was observed near 4.1 μm. As the pump power was increased, the QW spectra were observed to broaden and eventually saturate. Under low power pumping conditions, the OPSL pulse tracked the Ho:YAG pulse, which has a 16-ns full-width half-maximum. As the pump power was increased, the OPSL pulse duration increased and the pulse eventually split into two peaks. This may be due to a large increase in the free-carrier absorbance rates in the bulk-like quaternary absorber. Emission from the quaternary was observed near 2.2 μm and its intensity, with respect to the QW intensity, increased significantly as the pump power was increased. This indicates that at the higher pump powers, large fractions of photogenerated carriers are reservoired in the thick absorber layers. The maximum OPSL single-ended peak power was 490 W. This is the highest reported peak power from a mid-IR semiconductor laser. A rate equation model describing the time evolution of the carriers in the QW, the stored carrier population in the reservoir, and the photon population gives good agreement with the data.

Diode pumped high power operation of a femtosecond laser inscribed Yb:YAG waveguide laser [Invited

Waveguides were written into single crystalline Yb(7%):YAG with a femtosecond laser. Laser oscillation of the waveguides without external mirrors at an output coupling transmission of 99% was demonstrated. The laser performance of the waveguide lasers, pumped with various light sources, was examined. With an optically pumped semiconductor laser (OPS) as pump source a slope efficiency of 51% regarding incident pump power and a maximum output power of 1.76 W could be achieved. By using a high brightness DBR tapered diode laser as pump source the possible miniaturization of the waveguide laser device was demonstrated. With this pump source even 2.35 W of output power from the waveguide laser was achieved. The beam quality at highest output power turned out to be excellent with an M2-factor of less than 1.3.

Focus on lasers and imaging

Focus on lasers and imaging

OPSLs for quick flow cytometry

AbstractApplications for flow cytometry continue to diversify and evolve. That is because cytometry is both a widely used clinical tool for fast blood cell analysis as well as a powerful research tool. As novel therapeutic modalities (e. g. stem cell treatment) are developed, new cytometry applications often blur the traditional distinction between clinical and research measurements. Yet a single laser technology — the optically pumped semiconductor laser (OPSL) — is proving optimum in virtually all cases, whether the application needs high power, multiple wavelengths, low cost, small packaging or a low thermal or electrical budget. From routine counting of CD4 immune receptor cells to stem cell sorting, this article will show how and why OPSL is meeting the evolving needs of flow cytometry.

340-W Peak Power From a GaSb 2-$\mu$m Optically Pumped Semiconductor Laser (OPSL) Grown Mismatched on GaAs

A GaSb-based vertical external cavity laser at 2 μm was pumped by 100- to 160-ns pulses from a Nd : YAG laser at 1.064 μm operating at 1 kHz. It was shown that the output power scales with the pump spot diameter to the extent of our experiments. A peak output of over 340 W was obtained.

High-power, continuous-wave, optical parametric oscillator pumped by an optically pumped semiconductor laser at 532 nm

We report a high-power, cw, single-frequency optical parametric oscillator pumped external to an optically pumped semiconductor laser (OPSL). The singly resonant oscillator (SRO), based on a 30 mm crystal of MgO:sPPLT, is pumped by a 6 W, cw OPSL at 532 nm. By deploying signal outcoupling and loose focusing in the presence of low pump power, we achieve significant improvements in SRO performance across the tuning range with regard to signal power, extraction efficiency, and pump depletion by reducing thermal effects. We generate >1.78 W of idler and >0.9 W of signal over 856-1404 nm while maintaining a total output power of >2 W over 93% of the tuning range at an extraction efficiency of 48.7% and pump depletion of 84%. The signal power remains within 0.85-1.05 W across the entire tuning range and has a TEM(00) spatial profile with M(2)<1.28 and circularity of >97%. Measurements of signal spectrum confirm single-frequency performance with an instantaneous linewidth of approximately 15 MHz and frequency stability better than 60 MHz over 60 s.

Miniaturization and Power Scaling of Fundamental Mode Optically Pumped Semiconductor Lasers

We demonstrate that TEM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> mode optically pumped semiconductor lasers (OPSLs) may be scaled to tens of watts in the visible wavelength range using laser cavities an order of magnitude smaller than those of conventional solid-state lasers. In particular, we show that the output power may be scaled linearly by increasing the number of optically pumped semiconductor (OPS) devices and derive a unique solution for a dynamically stable resonator that is independent of the physical cavity length and internal design. This enables miniaturization of high-power OPS lasers to ~1 cm footprints without compromising many resonator performance metrics. The results are applied to demonstrate a 15-mm footprint cavity producing 7.3-W output at 486 nm, and a cavity with two OPS chips with 24-W output at 561 nm. In addition, we show that efficient TEM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> mode performance may be realized using free-space-coupled, high-power laser diode bars. Single-frequency operation is also demonstrated, and an rms noise level less than 0.01% is achieved.

Effect of pump laser noise on an erbium-doped fiber-amplified signal

The effect of pump laser noise on erbium-doped fiber-amplifier (EDFA) output was investigated using an optically pumped semiconductor laser (OPSL) as a high-power pump. Measurements included pump and amplified signal relative intensity noise (RIN) in frequency and time domains as well as gain spectral measurements and 10-Gb/s Q-factor tests, all under several levels of backreflection to the pump laser. Time-domain low-frequency noise (<50 kHz) was observed to increase with increasing backreflection. With 150-mW OPSL output power and -28 dB backreflection, temporal RIN was /spl sim/3.4% for the pump and /spl sim/2.2% for the amplified signal. At a maximum pump power of 450 mW, RIN was 1.4% and 1.1%, respectively. The measured Q-factor of 12.5 dB at 10 Gb/s showed less than 0.5-dB penalty compared to a back-to-back system measurement of 13 dB. Power budget and operating specifications of an OPSL-pumped multicoil EDFA were also evaluated.

Focus on Lasers and Optics

Focus on Lasers and Optics