Semiconductor lasers are ideal sources for efficient electrical-to-optical power conversion and for many applications where their small size and potential for low cost are required to meet market demands. Yellow lasers find use in a variety of bio-related applications, such as photocoagulation, imaging, flow cytometry, and cancer treatment. However, direct generation of yellow light from semiconductors with sufficient beam quality and power has so far eluded researchers. Meanwhile, tapered semiconductor lasers at near-infrared wavelengths have recently become able to provide neardiffraction- limited, single frequency operation with output powers up to 8 W near 1120 nm.
We present a 1.9 W single frequency laser system at 562 nm, based on single pass cascaded frequency doubling of such a tapered laser diode. The laser diode is a monolithic device consisting of two sections: a ridge waveguide with a distributed Bragg reflector, and a tapered amplifier. Using single-pass cascaded frequency doubling in two periodically poled lithium niobate crystals, 1.93 W of diffraction-limited light at 562 nm is generated from 5.8 W continuous-wave infrared light. When turned on from cold, the laser system reaches full power in just 60 seconds. An advantage of using a single pass configuration, rather than an external cavity configuration, is increased stability towards external perturbations. For example, stability to fluctuating case temperature over a 30 K temperature span has been demonstrated. The combination of high stability, compactness and watt-level power range means this technology is of great interest for a wide range of biological and biomedical applications.
3C (Chirally-Coupled Core) optical fiber establishes a technological platform for high brightness, power scalable lasers
with an engineerable fiber geometry that enables robustly single-mode performance of large core diameter fibers. Here
we report the demonstration of robust polarization preserving performance of 35 μm core 3C fiber for short pulse
systems. A polarization extinction ratio (PER) of ~ 20 dB is stably maintained with ambient temperatures varying over a
50°C range from a Yb-doped double clad 3C fiber amplifier. We also demonstrate that this high-PER polarization
output is insensitive to temperature gradients and mechanical perturbations in the 3C fiber amplifier. The ability to
deliver high peak power pulses at high average powers while maintaining exceptional beam quality and a stable
polarization state in an easily integrated format makes 3C fiber laser systems extremely attractive for harmonic
generation to visible and UV wavelengths.
Fiber lasers offer an excellent technology base for production of an industrial-quality tool for precision microfabrication, answering the need to expand the capabilities of laser material processing beyond traditional welding, cutting, and other industrial processes. IMRA's FCPA μJewelTM femtosecond fiber laser has been developed to address the particular need for direct-write lasers for creation of clean and high-quality micron and sub-micron features in materials of commercial interest. This flexible Yb:fiber chirped-pulse amplification architecture, capable of operating at rep-rates between 100 kHz and 5 MHz, balances the need for higher-repetition rate with that of sufficient pulse energy to work at or near ablation threshold, while meeting industrial standards for temperature, shock and vibration. Demonstration of the need for higher-repetition rates for direct write processes will be provided in this paper. Further, results of laser-processing of materials typically used in flat panel displays, photomasks, and waveguide production using the FCPA μJewelTM laser will be presented.
As applications demanding microJoule level pulses at "real-time" rates of delivery increase, and the expectations in terms of long-term, reliable, high quality performance become greater, fiber lasers are becoming increasingly attractive sources. When a combination of excellent beam quality, flexibility in design for repetition rate over 100 kHz - 5 MHz, and robust design for operation in a variety of environments, in a plug-and-play, non-water cooled package are necessary, IMRA’s fiber chirped-pulse amplifier (FCPA) system delivers in a compact, single-box solution. This type of laser has particular promise in precision material processing applications, enabling the use of technology that was previously considered too unstable or difficult to use. The basis for this advanced technology is a novel Yb:fiber oscillator/amplifier combination. The modular design architecture ensures a very robust construction that is well-suited to integration into commercial systems. To show the utility of such a laser in commercial applications, results of ablation thresholds and processing tests of various materials including metals and dielectrics are presented using IMRA’s FCPA μJewel femtosecond fiber laser.
Using an innovative approach based on Yb:fiber amplifiers and pre-shaped pulsed diode seeders, a unique laser source with tunable pulse duration and rectangular pulse shape has been developed. Based on the patented use of multimode fibers with single-mode output, the resultant system provides pulses adjustable between 4 and 20 ns duration with sharp rise times of < 1.5 ns, at a repetition rate of up to 20 kHz. The output pulse energy of > 15 microJoules can be maintained over the full tuning range. The high-quality output beam is coupled into a polarization-maintaining, single-mode delivery fiber for ease of integration into an application. With this "tailorable" pulse design, control of laser energy deposition in very confined laser interaction zones (by pulse shape), and of its dosage (by pulse duration) can be optimized by the user and adjusted in real-time from the laser controller in response to measured structural changes. Results of machining of materials such as Si, Cr on glass and drilling of Cu/Pl/Cu are presented, showing the unique capability of this laser and its advantageous use to ablate, structure, repair, or trim very small areas (down to sub-micron size) without damaging or influencing the underlying and/or neighboring structures.
On the basis of highly efficient Yb:fiber amplifiers, a new technology platform for compact and nearly maintenance-free laser sources from the femtosecond to the nanosecond time scale has been developed, allowing their application-customized use in industrial laser material processing. The core of this technology is the patented use of multimode fibers with TEM00 output characteristics, enabling high and efficient amplification while maintaining high quality of the output beam. First, we review the fiber laser amplifier developments in the femtosecond pulse regime. Then, we present for the first time a picosecond seed source, Yb fiber amplifier laser design. Next, we present a completely new laser seeder/amplifier design, enabling online temporal tuning of laser pulses between 4 and 20 ns without changing pulse energy by utilizing high-speed control circuitry to adjust pulse duration, repetition rate and pulse energy independently. Pulse length can be optimized to process a given dimension of a sample structure that needs to be modified. Pulse shape can be controlled to produce almost rectangular pulses with <1.5 ns rise times. The resultant pulses can be transported by a polarization-maintaining delivery fiber for easy integration and use in material processing applications. Finally, we describe a few examples of micromachining using pulses from this new, flexible, fiber-based nanosecond laser source.
We describe novel designs for production of laser pulses from the nanosecond to the femtosecond regime which allow optimization to specific material processing requirements. These lasers are based on use of multimode Yb:fiber amplifiers (MM YDFA) to provide microJoule-level output in a single-mode beam. First, we present laser designs based on MM YDFA that produce 10 kHz - 5 MHz pulses of picosecond and femtosecond duration. Next, by seeding a MM YDFA with pre-shaped nanosecond laser diode seed pulses, we have created a laser that provides temporally nearly-rectangular output pulses. The duration is adjustable between 4 and 20 ns, with sharp rise times of <1.5 ns, and repetition rate of up to 20 kHz. Output pulse energy of >15 microJoules is maintained over the full tuning range. With this "tailorable" pulse design, control of laser energy deposition in confined laser interaction zones (“dosage”) can be user-optimized in real-time from the controller. For example, in biomedical microelectronics and other applications where the creation of micron-size features (in width and in depth) is required the user can adjust dosage in response to meas-ured structural changes over the material. Results of Si wafer and other material micromachining using this unique tem-porally-tailored pulsed laser are presented.
High-power compact ultrafast pulse sources based on optical fiber lasers are discussed. The optical efficiency of fiber- based ultrafast pulse sources is optimized by the implementation of double-clad Yb-doped fibers. The spatial limitations of ultrafast single-mode fiber lasers and amplifiers are overcome by the implementation of diffraction-limited multi-mode rare-earth-doped fibers, allowing for the generation of ultrafast pulses with large peak powers. In the temporal domain, a further increase in obtainable peak powers is made possible by the use of chirped pulse amplification or the amplification of pulses with parabolic temporal profiles. Parabolic pulses are generated in the asymptotic limit in high gain fiber amplifiers operating in the positive dispersion regime.
Microjoule pulse energies are achieved from a single stage upconversion fiber amplifier for the first time in this demonstration of chirped pulse amplification using a multimode Tm:ZBLAN fiber. A Ti:sapphire laser system provides the seed pulse for the upconversion fiber amplifier which produces subpicosecond pulse trains with energies as great as 16 (mu) J at repetition rate of 4.4 kHz. The compressed pulse peak power is more than 1 MW, and the pulse is characterized both temporally and spatially.
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