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We have demonstrated a highly-efficient cladding-pumped ytterbium-doped fiber laser generating 1.36 kW of continuous-wave output power at 1.1 mum with 83% slope efficiency and near diffraction-limited beam quality. The laser was end-pumped through both fiber ends and showed no evidence of roll-over even at the highest output power, which was limited only by available pump power.

Over the last few years there has been increasing interest in power-scaling of fibre-based sources operating in the eyesafe two-micron wavelength regime driven by a range of applications. Much of this interest has focussed on Tm-doped silica fibres which offer wide spectral coverage from ∼1.7 µm to ∼2.1 µm [1], a range of pump wavelengths and the potential to be scaled to very high powers [2]. By contrast, far less attention has been directed towards Ho-doped silica fibres which also offer a very wide range of emission wavelengths extending well beyond 2.1 µm. However, scaling the output power from Ho-doped silica fibres is hindered by the fact that there is no absorption band that coincides with the emission wavelengths available from high-power (near-infrared) commercially available diode pump sources. One solution to this problem is to add Tm to the core to act as a sensitiser. In this way pump light from high-power laser diodes at ∼0.8 µm is absorbed by the Tm ions and the Ho ions in-directly excited by energy-transfer from the Tm ions. Using this approach, Jackson et al. recently reported 83 W of output from a cladding-pumped Tm, Ho co-doped fibre laser [2]. Co-doping with Tm however leads to very strong energy-transfer-upconversion and hence a reduction in the effective upper-state lifetime. The net result is additional heat loading leading, lower efficiency and limited flexibility in mode of operation. An alternative approach is to use a high-power cladding-pumped Tm fibre laser to pump a Ho-doped fibre laser avoiding the need for co-doping with Tm [4]. This has the attraction a very low quantum defect pumping scheme can be employed in the Ho fibre laser allowing very high lasing efficiencies to be achieved and offering the potential to be scaled to very high power levels. In this paper, we report preliminary results for a Ho silica fibre laser operating at 2090 nm in-band pumped by a cladding-pumped Tm doped fibre laser at 1980 nm.

Photodarkening (PD) in optical fibers is a serious concern for the development and maintenance of the reliable operation of high-power ytterbium fiber lasers (YDFL), over a long period of time. Formation of colour centres in the silica glass host is often believed to be the reason behind PD [1]. Yb-doped aluminosilicate fiber suffers PD as a permanent excess optical loss (unless optically or thermally photobleached) having a low-energy absorption tail extending into the 0.9–1.0 µm absorption band and 1.1 µm emission band of YDFLs [2,3]. Our previous studies emphasised on oxygen deficient centres (ODC) as a precursor of PD in Yb-doped aluminosilicate fiber [4] under a 488 nm CW pump and also revealed the post-irradiation temporal evolution of the induced loss [5]. To the best of our knowledge, our present report is the first of its kind to show the temperature dependance of the post-irradiation induced excess loss in VIS-NIR in Yb-doped aluminosilicate fiber, even after stopping the 488 nm CW pump.

High power fibre sources have reached several kilowatts of output power. Besides power, control, efficiency, manufacturability, and reliability are important attractions. We will discuss these unique properties and their exploitation.

The feasibility of direct laser diode pumping of Bi-doped fiber lasers at the wavelengths of 915 and 975 nm was examined by measuring excited state absorption in Bi-doped silicate fibers for the wavelength range of 900-1250 nm. When the Bi-doped fibers were pumped at 1047 nm a strong excited state absorption was found at 915 and 975 nm, whereas no significant excited state absorption was observed in the 1080 nm pumping band nor in the emission band, approximately 1160 nm, of Bi-doped fiber lasers.

The development of low loss, rare-earth doped, silica fibers in the mid-1980s revolutionized optical communications through the discovery of erbium-doped fiber amplifiers (EDFAs). Following the successful implementation of EDFAs in communications, high-power cladding pumped fiber lasers and amplifiers have, over the last decade, become a major field of operation of rare-earth doped fibers that now significantly opens up the use of fiber lasers in non-telecommunications markets. Fiber lasers benefit from a waveguide geometry that facilitates tight confinement of pump and signal beams over arbitrary length, providing characteristics such as low threshold, an output that can be easily tailored to produce single-spatial mode operation, a feasible three-level system, a broad gain bandwidth, and a high overall gain compared to bulk lasers. In recent years, the output power of fiber laser sources has been significantly increased to the point where the fiber based technology is now competing with conventional bulk solid-state lasers in applications such as micro-machining, welding and other material processing. In particular, ytterbium-doped fiber lasers have been power-scaled to several kilowatts at ~1.1 µm, with a nearly diffraction-limited output beam. In the power scaling process, nonlinear scattering such as stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) are viewed as the main challenges to overcome. Novel fiber devices, including those at other wavelengths and with different spectral properties have seen rapid progress. This presentation will review the progress in active fibers suitable for power scaling, highlighting the advances in fiber design and fabrication that will enable the control of nonlinearities in high power fiber lasers, as well as make feasible of a practical high power three-level system.

Thulium-doped silica fiber lasers and amplifiers offer a route to very high average power in the two-micron wavelength regime. This presentation reviews recent progress and considers the prospects for further improvement in performance.

A Tm-doped fiber master-oscillator power-amplifier system that generates over 100W of single frequency output in a near-diffraction-limited beam with an M2 parameter of 1.25 is described. The prospects for further increase in power are considered.

We investigated the performance of Bi-doped fiber amplifier at 1179 nm, in both low and high input signal regime, when pumped at 1090 nm. The amplifier efficiency and the saturation power both depend on the fiber cooling.

We investigate the thermal characteristics of a polymer-clad fiber laser under natural convection when it is strongly pumped up to the damage point of the fiber. For this, we utilize a temperature sensing technique based on a fiber Bragg grating sensor array. We have measured the longitudinal temperature distribution of a 2.4-m length ytterbium-sensitized erbium-doped fiber laser that was end-pumped at approximately 975 nm. The measured temperature distribution decreases exponentially, approximately, decaying away from the pump-launch end. We attribute this to the heat dissipation of absorbed pump power. The maximum temperature difference between the fiber ends was approximately 190 K at the maximum pump power of 60.8 W. From this, we estimate that the core temperature reached approximately 236 degrees C.

A narrow-linewidth mid-IR source based on difference-frequency generation of an amplified 1.5 microm diode laser and a cw Tm-doped fiber laser in orientation-patterned (OP) GaAs has been developed and evaluated for spectroscopic applications. The source can be tuned to any frequency in the 7.6-8.2 microm range with an output power of 0.5 mW. The measured characteristics of the OP-GaAs sample demonstrate a high quality of the material.

In this work a volume Bragg grating is used as a wavelength selective element in a high-power cladding-pumped Yb-doped silica fiber laser. The laser produced 138 W of linearly-polarized single-spatial-mode output at 1066 nm with a relatively narrow linewidth of 0.2 nm for approximately 202 W of launched pump power at 976 nm. The beam propagation factor (M(2)) for the output beam was determined to be 1.07. Thermal limitations of volume Bragg gratings are discussed in the context of power scaling for fiber lasers.

In the recent years some tremendous progresses have been made to scale up the output power of fiber laser to the point where fiber laser technology is becoming a serious competitor to the solid-state lasers in most of the industrial applications. Nowadays single mode Ytterbium (Yb) doped fiber lasers with an output power of 2kW[1] are commercially available and some 5kW systems are a reality in the laboratory environment. Unfortunately the scaling of laser systems up to increasingly higher power levels is limited by some nonlinear effects like Raman which degrade the laser efficiency or the thermo-optics effect which degrade the beam quality. Even if the fiber laser technology is able to overcome these problems to a certain degree, it is desirable to increase the system power levels beyond what is possible with a single fiber laser. One promising technology that is being studied to achieve this is to combine a large number of relatively lower power beams into a single high-power beam. In order to be effective, this technique requires that each single low power laser has to be single polarization, single mode and single frequency.

Efficient high-power operation of double-clad Er,Yb-doped fiber lasers with fixed-wavelength and wavelength-tunable resonator configurations using volume Bragg gratings for wavelength selection are reported. The fixed-wavelength laser yielded a maximum output power of 103 W at 1552.6 nm with a linewidth of ~0.4 nm (FWHM) for a launched pump power of 290 W at 976 nm. The wavelength-tunable laser could be tuned from 1528 to 1550 nm with a linewidth of 0.2 nm (FWHM) and with output power in the range 30-38 W for a launched pump power of 120 W. The prospects for further improvement in performance are considered.

Modal interference in few-moded large-core fiber amplifiers can yield output beams with good beam quality (M2~1.2 - 1.4) giving the impression of single-mode operation despite significant higher-order mode content. The implications for high-power devices are discussed.

Recently developed novel psilaflat fiberpsila substrate promises flexible, long-haul integrated optical devices. Here, we present the first demonstration of one such device; an evanescent field sensor, based upon direct UV written Bragg gratings.

We report an Er:YAG ring laser employing an acousto-optic modulator to enforce unidirectional operation. The laser yields 4.7 W of single-frequency output at 1645 nm in a beam with M2~1.03 for 14 W of pump power at 1532 nm.

We report a 210 muJ pulsed high-brightness fiber source based on a cladding-pumped Raman fiber. It delivers Stokes light at 1112 nm, of 500 ns duration, 420 W peak power, and M2 1.8.

We report high-power operation of double-clad Yb-doped and Er,Yb-doped fiber lasers at 1066 nm and 1553 nm respectively using volume Bragg gratings for wavelength selection. Both lasers yielded output powers over 100 W limited by available pump power.

Using a hybrid fiber-bulk laser scheme based on Er:YAG, we have achieved ~60 W and ~30 W of continuous-wave output at 1645nm and 1617nm respectively, and Q-switched pulse energies up to ~30 mJ (limited by coating damage). Investigation of various factors influencing laser performance has revealed that energy-transfer-upconversion can have a very detrimental impact on efficiency, even in continuous-wave mode of operation. In this paper we report on the results of this study, discuss various measures for reducing energy-transfer-upconversion and its effect on laser performance, and consider the prospects for further increase in output power and pulse energy.

Photodarkening of Yb-doped aluminosilicate fibers by continuous wave 488 nm irradiation was investigated. The irradiation induced significant excess loss in the UV-visible spectroscopy (VIS) region in Yb-doped aluminosilicate fibers while pure aluminosilicate fibers showed negligible induced loss. Ultraviolet-VIS-near infrared spectroscopy revealed an absorption peak at 220 nm in unexposed Yb-doped aluminosilicate fiber preforms. The observed peak was attributed to Yb-associated oxygen deficiency centers (ODCs) and proposed as a precursor of the photodarkening. The proposed model was supported by measurements on oxygen loaded Yb-doped aluminosilicate fibers. In these, the photodarkening could be significantly reduced, which we attribute to a smaller number of ODCs following oxygen loading.

Optical fibre end termination techniques are very important in the development of fibre-based optical communication systems and high-power fibre sources in laser, amplifier and superfluorescent configurations. There are many situations where unwanted optical feedback from a fibre end-facet can be very detrimental to the performance of the fibre source. For example, in laser configurations in which an external cavity is employed to extend the functionality (e.g. for Q-switching, mode-locking or wavelength tuning), then feedback from the fibre end-facet adjacent to the external cavity will compete with the feedback provided by the external cavity itself and hence may impact adversely on the laser output characteristics.

High-power operation of fiber-based ASE sources is reported. Using single-stage and two-stage cladding-pumped ytterbium-doped fiber configurations we obtained 62 W and 122 W of broadband ASE output respectively. The prospects for further improvement in performance are considered.

Progress in active fibers for high power fiber sources is discussed. The waveguiding geometry naturally lends itself to high-power diffraction-limited operation. Further refinements allow for the control of nonlinearities and wavelength. Fabrication advances mitigate photodarkening.

Over recent years, there has been a tremendous and rapid progress in power scaling Yb-doped fiber-based picosecond sources due to their high efficiency, excellent beam quality and immunity to thermo-optical effects. These remarkable properties are not only very attractive for many scientific and industrial applications but also for frequency doubling to generate green. Besides good beam quality, a high degree of polarization and a narrow linewidth, further increase in conversion efficiency requires high peak power and increased crystal length. High peak power can be obtained by employing a fiber master-oscillator power amplifier design (MOPA) where seed pulses with adequate duty cycle are amplified to high average powers. However in this arrangement minimizing nonlinear effects arising in the fiber amplifiers becomes a challenge. The amplification of picosecond pulses causes linewidth broadening and the spectral bandwidth of the crystal is reduced by a preferred longer length. This trade-off can result in lower frequency doubling efficiency. In this paper, as well as the benefits and limitations of fiber lasers applied to nonlinear frequency conversion, we will review the various design considerations for the development of a high average power picosecond green laser based on single-pass frequency doubling of a fiber MOPA system.

An in-band pumped thulium-doped distributed-feedback fiber laser is reported. The laser produced 318 mW of output power at 1935 nm with a slope efficiency of 21% with respect to absorbed pump power.

We discuss fundamental aspects and future prospects of high power fiber lasers and amplifiers with particular attention to high control of cladding-pumped, rare-earth-doped fiber sources in a multitude of regimes.

Integrated optical devices offer dense, multifunctional capability in a single robust package but are rarely considered compatible with the fields of remote or distributed sensing or long-haul 'one-dimensional' fibers. Here we aim to change that by introducing a 'flat-fiber' process that combines the advantages of existing low-cost fiber drawing with the functionality of planar lightwave circuits in a novel hybrid format. By taking this approach, we hope to extend beyond the limitations of traditional planar and fiber substrates - allowing exotic material compositions, device layouts, and local sensing functions to be distributed over extended distances with no coupling or compatibility concerns in highly functional distributed lab-on-a-chip devices.

We experimentally demonstrate an all-solid Yb-doped 30 μm core diameter single trench fiber. Measurements ensure a robust effective single-mode operation without the need of tight coiling as required for conventional fibers thanks to the ultralow NA (∼0.038) and resonant ring surrounding the core. All-solid and cylindrical design ensures the suitability for mass scale production with the added benefit of all-fiberized device structure. A compact master oscillator power amplifier (MOPA) has been built using this fiber delivering ∼23.5 ps pulses at 13.5 MHz repetition rate delivering up to ∼52 W of average output power corresponding to a pulse energy of ∼3.8 μJ and peak power of160 kW, while maintaining ∼76% slope efficiency. The output beam exhibits a polarization extinction ratio of more than 15 dB and a M2 less than 1.15.

Bismuth-doped aluminosilicate fiber has been fabricated by the MCVD-solution doping method and characterized for its unsaturable loss and gain. The amplifier performance has been compared for a novel pumping wavelength of 1120 nm with the conventional pumping wavelength region of 1047 nm. Unsaturable loss was 65% and 35% at 1047 and 1120 nm, pump wavelengths, respectively. A maximum gain of about 8 dB at 1180 nm for a fiber length of 100 m was observed with 1120 nm pumping. Gain enhancement of 70% was achieved with the 1120 nm pump as compared to the 1047 nm pump. A further 3.5 dB gain was obtained on simultaneous pumping at 1047 and 1120 nm.

In this paper, we report the mode area scaling of a rare-earth doped step index fiber by using low numerical aperture. Numerical simulations show the possibility of achieving an effective area of ~700 um² (including bend induced effective area reduction) at a bend diameter of 32 cm from a 35 μm core fiber with a numerical aperture of 0.038. An effective single mode operation is ensured following the criterion of the fundamental mode loss to be lower than 0.1 dB/m while ensuring the higher order modes loss to be higher than 10 dB/m at a wavelength of 1060 nm. Our optimized modified chemical vapor deposition process in conjunction with solution doping process allows fabrication of an Yb-doped step index fiber having an ultra-low numerical aperture of ~0.038. Experimental results confirm a Gaussian output beam from a 35 μm core fiber validating our simulation results. Fiber shows an excellent laser efficiency of ~81%and aM² less than 1.1.

High-power operation of a broadband superfluorescent fiber source has been achieved via the process of amplified spontaneous emission (ASE) in a double-clad Yb-doped multimode-offset-core fiber by using a novel fiber-end termination geometry to suppress lasing. The fiber was cladding pumped by a high-power diode source at 976 nm and yielded a maximum ASE output of 63 and 47 W from the two ends of the fiber, respectively. The maximum combined ASE output was 110 W with slope efficiency with respect to launched pump power of up to 68%. The wavelength spectrum of the ASE source spanned the range from approximately 1032 to 1120 nm, and the bandwidth (FWHM) of the emission spectrum was 40 nm. The output beam was slightly multimode with a beam-quality factor (M2) of 1.6. The prospects for further improvement in performance are considered.

Fiber lasers and amplifiers offer unique characteristics that are derived from the use of a waveguide and the properties of rare-earth doped silica glass. Their capability for high output power, with high efficiency, has been demonstrated both in CW and pulsed regimes. Cladding-pumped Yb-doped fiber lasers have now reached beyond kW levels with good beam quality. Advances in both fiber technology and high-power multimode diode pump sources, and the inherent power scalability of cladding-pumped fibers, lie behind this power surge. However, there are still many challenges to overcome in the high-power fiber laser area. These include, for example, single-mode output at higher powers and power scaling of a three-level laser. This paper reviews novel W-type fiber and depressed clad hollow optical fiber waveguide structures designed with distributed wavelength filter characteristics to achieve an efficient and high power cladding-pumped three-level lasers such as Nd-doped fiber laser operating at 930 nm and Yb-doped fiber laser at 980 nm. Moreover, such fiber geometries enable to scale up the output power in a small and single-mode core for generating a single-mode output beam in a robust and reliable manner.

Fiber amplification of sub-picosecond pulses at 1.1 GHz produced by a passively mode-locked VECSEL enabled the generation of parabolic pulses with average power exceeding 50 W. Clean pulse compression down to 110 fs was demonstrated.

First demonstration of planar Bragg gratings UV written into collapsed fibre planar samples with ≫200?m cladding thickness is presented. Multiple gratings were written across the sample profile to accurately determine core layer flatness and uniformity.

High power operation of an ytterbium-doped multi-core ribbon fiber laser and a cladding pumped ytterbium-doped helical core fiber laser is reported. 320W laser output at 1045nm was demonstrated with a 10-core ytterbium doped ribbon fibre. Efficient single-mode operation of a cladding-pumped ytterbium-doped helical-core fiber laser with a 30 µm diameter core and a numerical aperture of 0.087 have also been demonstrated. The laser yielded 60.4 W of output at 1043 nm in a beam with M 1.4 for 92.6 W launched pump power from a diode stack at 976 nm. Further more, the recently progress of a cladding-pumped ytterbium-doped helical-core superfluorescent fiber source is also reported. The highly efficient operation of the helical core fiber ASE source yielded 107W of amplified spontaneous emission output spanning the wavelength range from 1030-1160nm with a bandwidth (FWHM) of 37nm.

We report on recent progress in power scaling of cladding-pumped Er,Yb and Tm-doped silica fiber lasers in the ~1.5μm and ~2μm spectral regimes respectively, and also on some recent developments in fiber-bulk hybrid lasers based Er:YAG and Ho:YAG operating at ~1.6μm and ~2.1μm respectively. A cladding-pumped Tm-doped silica fiber laser pumped by a beam-shaped diode-stack at 790nm and with core composition optimized for efficient 'two-for-one' cross-relaxation yielded 66W of continuous-wave output at ~2μm for 117W of launched pump power. The corresponding slope efficiency with respect to launched pump power was 61%. An Er,Yb fibre laser, cladding-pumped by two spatially-multiplexed diode-stacks at 976nm and with core composition optimized for efficient energy-transfer from Yb3+ to Er3+, yielded up to 188W of continuous-wave output at 1570nm with an average slope efficiency with respect to launched pump power of 41%. The prospects for a further increase in output power from Tm and Er,Yb fiber lasers are considered. Efficient operation of hybrid Er:YAG and Ho:YAG lasers, pumped in-band by Er,Yb and Tm doped fibre lasers operating at 1532nm and 1907nm respectively has been demonstrated. Both lasers, when operated in continuous-wave mode, had slope efficiencies with respect to incident pump power of ~80%. The Er:YAG laser produced ~60W of continuous-wave output at 1645.3nm for 82 W of incident pump power, and, in Q-switched mode, produced pulses of energy, ~5.5mJ and duration, ~81ns (FWHM) corresponding to a peak power of ~67kW at a repetition rate of 500Hz for an incident pump power limited by the onset damage to 16.8W. The prospects for further improvement in continuous-wave and Q-switched performance are discussed.

We propose a depressed clad hollow optical fiber with fundamental (LP01) mode cut-off suitable for high power short-wavelength, especially three-level, fiber laser operation by introducing highly wavelength dependent losses at longer wavelengths. The cut-off characteristic of such fiber structure was investigated. A Yb-doped depressed clad hollow optical fiber laser generating 59.1W of output power at 1046nm with 86% of slope efficiency with respect to the absorbed pump power was realised by placing the LP01 mode cut-off at ~1100nm.

A novel approach to achieving robust single-spatial-mode operation of cladding-pumped fiber lasers with multimode cores is reported. The approach is based on the use of a fiber geometry in which the core has a helical trajectory within the inner cladding to suppress laser oscillation on higher-order modes. In a preliminary proof-of-principle study, efficient single-mode operation of a cladding-pumped ytterbium-doped helical-core fiber laser with a 30 microm diameter core and a numerical aperture of 0.087 has been demonstrated. The laser yielded 60.4 W of output at 1043 nm in a beam with M21.4 for 92.6 W launched pump power from a diode stack at 976 nm. The slope efficiency at pump powers well above threshold was approximately 84%, which compares favorably with the slope efficiencies achievable with conventional straight-core Yb-doped double-clad fiber lasers.

Fibre lasers are thin, light-guiding strands of glass only a few times the thickness of a hair which have a tiny core doped with rare-earth materials to absorb the pump radiation and release the stimulated emission at the signal wavelength. Fibre lasers provide unheard of attributes in the laser world – low maintenance, high efficiency, and excellent beam control, and are compact and all-solid-state. Their low cost of ownership will enable industrial laser applications, such as material processing, micro-machining, marking, printing, medicine, etc., which were hitherto thought impractical.

In this paper, we report highly efficient operation of Tm-doped silica fibre lasers, pumped by a high-power cladding-pumped Er,Yb fibre laser at 1565 nm, in both cladding-pumped and core-pumped resonator configurations. In the cladding-pumped Tm fibre laser we obtained up to 19 W of output at 1991 nm with a slope efficiency of 69% with respect to absorbed pump power, and in the core-pumped laser we obtained a maximum output power of 12.1 W at 1860 nm limited by available pump power. Using tunable cavity configurations the cladding-pumped and core-pumped Tm fibre lasers could be tuned from 1861 to 2061 nm and from 1725 to 1973 nm at multi-watt power levels respectively

Over the last few years there has been very rapid progress in scaling output power from cladding-pumped fibre lasers and amplifiers [1]. One of the key issues to address for further power-scaling of single-mode operation will be to increase the core area in order to avoid the need for excessively long fibres for efficient pump absorption, and to raise the threshold for unwanted nonlinear processes and optical damage, whilst maintaining robust single-mode operation. At the moment, this is generally achieved by employing a multimode large-mode-area core design with a low numerical aperture in combination with bend loss suppression of higher-order modes [2] to promote single-mode operation. However, scaling to higher power levels will require an even larger core diameter and a larger inner-cladding diameter to accommodate more pump power, making it increasingly difficult to coil the fibre with a small enough diameter to use bend-induced loss as an effective means for suppressing higher-order modes. An alternative approach for achieving single-mode operation in a large-core fibre laser/amplifier is to employ a fibre with a helical core trajectory within the inner-cladding. In a preliminary demonstration of this approach, we recently reported a core-pumped Yb-doped helical-core fibre laser with 350mW of single-mode output at 1047nm [3]. Here, we report a highly efficient cladding-pumped Yb-doped helical-core fibre laser at 1043nm with a much higher single-mode output power of ~60.4W and preliminary results for a cladding-pumped Yb-doped helical-core fibre amplifier seeded by a single-mode Yb:YAG laser at 1050nm.

We discuss fundamental aspects of high-power fiber lasers and describe their recent dramatic advances and prospects including our up-to-date experimental results with particular attention to kilowatt-class, refined power amplifier regimes.

We report 5-ps pulses at 160 W average power and 910 MHz repetition rate from a passively mode-locked VECSEL source seeding an Yb-doped fibre power amplifier. The amplified pulses were compressed to 291 fs duration.

Suppression of stimulated-Raman-Scattering in a 100 ps, 32 MHz pulsed fiber source is demonstrated. 12.5 kW of peak power was achieved in a small core single-mode ytterbium-doped fiber amplifier where the stimulated-Raman-scattering was efficiently filtered out by a W-type waveguide structure.

Electro-optically Q-switched operation of an Er:YAG laser at 1645 nm end-pumped by a cladding-pumped Er,Yb fiber laser is reported. Pulse energies up to 15 mJ have been generated at a pulse repetition frequency of 29Hz.

Cladding-pumped fibre lasers are becoming increasingly attractive for high power generation due to their high efficiency and immunity from thermal effects. However, due to their small core size and long device length, pulse energies are rather limited. In contrast, conventional 'bulk' solid-state lasers offer the prospect of much higher pulse energies, but suffer from detrimental thermal effects which can degrade beam quality and efficiency. An alternative strategy for scaling output power and pulse energy, which is attracting growing interest, is to use a hybrid laser scheme. In this approach, the fibre laser is used as a high-brightness source for in-band pumping of a bulk solid-state laser. One of the main attractions of the fiber-bulk hybrid laser scheme is that most of the heat generated via quantum defect heating is deposited in the fibre, and thermal effects in the bulk laser are dramatically reduced leading to the prospect of much improved efficiency, beam quality, higher average output power and high pulse energy. This approach has already been successfully applied to a number of different solid-state lasers operating in the eyesafe wavelength regimes around 1.6 μ and 2 μm. This presentation will review recent progress in power scaling of hybrid lasers in cw and in pulsed modes of operation, and will consider the prospects for further improvement in performance.

A picosecond single-mode, linearly polarized fiber source producing 176 W of average power was employed to generate up to 80 W average power at 530 nm by frequency doubling through a single LBO crystal.

We report a 10 W continuous-wave cladding-pump Raman fiber laser with single-mode output at 1660 nm pumped by a high-power Er:Yb fiber amplifier. The laser threshold was 6.5 W and its slope efficiency was 67%.

We review the recent dramatic advances in high power single-frequency Yb doped fiber amplifiers and discuss fundamental aspects and future prospects. We present up-to-date experimental results with particular attention to cladding-pumped, refined power amplifier regimes.