After the invention of lasers, in the past 50 years progress made in laser-based display technology has been very promising, with commercial products awaiting release to the mass market. Compact laser systems, such as edge-emitting diodes, vertical-cavity surface-emitting lasers, and optically pumped semiconductor lasers, are suitable candidates for laser-based displays. Laser speckle is an important concern, as it degrades image quality. Typically, one or multiple speckle reduction techniques are employed in laser displays to reduce speckle contrast. Likewise, laser safety issues need to be carefully evaluated in designing laser displays under different usage scenarios. Laser beam shaping using refractive and diffractive components is an integral part of laser displays, and the requirements depend on the source specifications, modulation technique, and the scanning method being employed in the display. A variety of laser-based displays have been reported, and many products such as pico projectors and laser televisions are commercially available already.

/pdf/laser-based-displays-a-review-4g00j2f2g3.pdf

Laser-based displays: a review

By doping an organic compound functioning as an electron donor (hereinafter referred to as donor molecules) into an organic compound layer contacting a cathode, donor levels can be formed between respective LUMO (lowest unoccupied molecular orbital) levels between the cathode and the organic compound layer, and therefore electrons can be injected from the cathode, and transmission of the injected electrons can be performed with good efficiency. Further, there are no problems such as excessive energy loss, deterioration of the organic compound layer itself, and the like accompanying electron movement, and therefore an increase in the electron injecting characteristics and a decrease in the driver voltage can both be achieved without depending on the work function of the cathode material.

Light Emitting Device

The performance of ultrafast semiconductor disk lasers has rapidly advanced in recent decades. The strong interest from industry for inexpensive, compact, and reliable ultrafast laser sources in the picosecond and femtosecond domains has driven this technology toward commercial products. Frequency metrology and biomedical applications would benefit from sub-200-femtosecond pulse durations with peak powers in the kilowatt range. The aim of this review is to briefly describe the market potential and give an overview of the current status of mode-locked semiconductor disk lasers. Particular focus is placed on the ongoing efforts to achieve shorter pulses with higher peak powers. As small, ultrashort-pulse lasers with high peak powers, semiconductor thin-disk lasers hold promise for spectroscopy, metrology and imaging. Bauke Tilma and co-workers from ETH Zurich review recent progress in developing such lasers for these applications. They report how the latest designs of external-cavity disk lasers that are passively mode locked using a saturable absorber now offer repetition rates of up to 100 gigahertz, pulse durations of shorter than 200 femtoseconds and peak powers in the kilowatt range. The compact design, excellent noise performance and customizable emission wavelength of such sources make them highly attractive for a variety of applications. Future research into the materials providing the optical gain and saturable absorption in such lasers is likely to further improve their efficiency, reliability and thermal stability.

/pdf/recent-advances-in-ultrafast-semiconductor-disk-lasers-5dtnx3yedw.pdf

Recent advances in ultrafast semiconductor disk lasers

A review on the recent developments in the field of long-wavelength (A > 1.2 μm) high-brightness optically-pumped semiconductor disk lasers (OPSDLs) is presented. As thermal effects have such a crucial impact on the laser performance particular emphasis is given to modelling the thermal behaviour and optimisation of the heat-sinking. Selected OPSDL devices, realized in different III-V and IV-VI semiconductor material systems, with corresponding emission wavelengths between 1.2 μm and 5.3 μm are presented. Specific applications in this broad spectral range are addressed and methods to obtain high output power are discussed in terms of the underlying material properties and device operating principles.

High-brightness long-wavelength semiconductor disk lasers

An optically pumped semiconductor disk laser using submonolayer quantum dots (SML QDs) as gain medium is demonstrated. High-power operation is achieved with stacked InAs∕GaAs SML QDs grown by metal-organic vapor-phase epitaxy. Each SML-QD layer is formed from tenfold alternate depositions of nominally 0.5 ML InAs and 2.3 ML GaAs. Resonant periodic gain from a 13-fold nonuniform stack design of SML QDs allows to produce 1.4W cw at 1034nm. The disk laser demonstrates the promising potential of SML-QD structures combining properties of QD and quantum-well gain media for high-power applications.

High-power semiconductor disk laser based on InAs /GaAs submonolayer quantum dots

The authors report the demonstration of highly efficient continuous-wave green light at 535nm generation by intracavity frequency doubling of an end-pumped vertical external-cavity surface emitting semiconductor laser (VECSEL). The beta-barium borate (β-BaB2O4) crystals, cut for critical type I phase matching at room temperature, are used for second harmonic generation of the laser. In combination with an end-pumped VECSEL and efficient intracavity frequency doubling with a folded three-mirror cavity, more than 7W green light output power is obtained at pump power of 26W. The optical conversion efficiency of 27% is achieved from pump power to second harmonic power.

7W high-efficiency continuous-wave green light generation by intracavity frequency doubling of an end-pumped vertical external-cavity surface emitting semiconductor laser

The authors report on the development and demonstration of the high power operation of optically end-pumped vertical external cavity surface emitting laser devices emitting at 532 and 460nm. 2.7W green and 1.4W blue output powers were achieved with a good beam quality by intracavity frequency doubling with second harmonic generation crystal. High efficiency and good beam quality are attributed to the enhanced thermal management by the diamond heat spreader directly bonded to the gain region and effective optical pumping by placing the pump laser diode behind the laser structure.

End-pumped green and blue vertical external cavity surface emitting laser devices

We report on the demonstration of highly efficient blue lasers based on intracavity frequency doubling vertical-external-cavity surface-emitting lasers (VECSELs). By optimizing the number of InGaAs quantum wells and employing Al0.3Ga0.7As carrier blocking layers in resonant periodic gain structures, we observed the pump-power-limited output power of 4.5W at 920nm for an InGaAs∕GaAs quantum well VECSEL. With a frequency doubling LiB3O5 crystal inside the cavity, 1.9W continuous-wave 460nm blue output was demonstrated. Power conversion efficiencies (=output power∕pump input power) of 22.5% and 9.5% are realized for λ∼920nm and λ∼460nm, respectively.

Efficient blue lasers based on gain structure optimizing of vertical-external-cavity surface-emitting laser with second harmonic generation

Provided is a VECSEL capable of achieving an excellent efficiency of a SHG crystal and being manufactured in a compact size. The VECSEL includes a laser chip, an external mirror, an SHG crystal, a lens element, and a wavelength selective mirror. The laser chip generates a first wavelength light, and the external mirror is spaced from the laser chip to face the front side of the laser chip. The SHG crystal is located between the external mirror and the laser chip to double the frequency of the first wavelength light to make a second wavelength light. The lens element is located between the SHG crystal and the laser chip to allow the first wavelength light generated from the laser chip to converge at the SHG crystal, and the wavelength selective mirror is located between the SHG crystal and the lens element to transmit the first wavelength light and reflect the second wavelength light to the external mirror.

Vertical external cavity surface emitting laser

We report the first demonstration of an end-pumped vertical-external-cavity surface-emitting semiconductor laser (VECSEL) with more than 9.1-W continuous-wave output power at a wavelength of 1079 nm. In order to enable the VECSEL to operate in an end-pumping scheme, a liquid capillary bonding method is used to bond the VECSEL chip to the surface of an optically transparent heat spreader. Moreover, a modified distributed Bragg reflector is applied to the VECSEL chip structure to maximize the pump efficiency. These will result in an end-pumped VECSEL that is characterized by high output power with good beam quality without additional antireflection coatings of the samples. In combination with an end-pumped scheme and desirable output beam, the end-pumped VECSEL will prove useful in a variety of applications requiring compact module and efficient source with high output power

9.1-W High-Efficient Continuous-Wave End-Pumped Vertical-External-Cavity Surface-Emitting Semiconductor Laser

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