High-brightness Diode Lasers Research Articles

Compact sub-100-fs Nd:silicate laser

We present a compact Nd:silicate laser pumped by a single 1-W high-brightness commercial laser diode that generates pulses as short as 88fs (nearly Fourier limited) when passively mode-locked with a saturable absorber mirror. We also tested a prismless cavity setup employing a single Gires–Tournois mirror, yielding 100-fs pulses. These setups are significantly simpler and more compact than those reported previously for short pulse Nd:silicate lasers.

Design and Simulation of Next-Generation High-Power, High-Brightness Laser Diodes

High-brightness laser diode technology is progressing rapidly in response to competitive and evolving markets. The large volume resonators required for high-power, high-brightness operation makes their beam parameters and brightness sensitive to thermal- and carrier-induced lensing and also to multimode operation. Power and beam quality are no longer the only concerns for the design of high-brightness lasers. The increased demand for these technologies is accompanied by new performance requirements, including a wider range of wavelengths, direct electrical modulation, spectral purity and stability, and phase-locking techniques for coherent beam combining. This paper explores some of the next-generation technologies being pursued, while illustrating the growing importance of simulation and design tools. The paper begins by investigating the brightness limitations of broad-area laser diodes, including the use of asymmetric feedback to improve the modal discrimination. Next, tapered lasers are considered, with an emphasis on emerging device technologies for applications requiring electrical modulation and high spectral brightness.

ボリュームブラッグ格子を用いた高輝度狭帯域外部共振器半導体レーザー

ボリュームブラッグ格子を用いた高輝度狭帯域外部共振器半導体レーザー

Quasi-three-level solid-state lasers in the near and mid infrared based on trivalent rare earth ions

Quasi-three-level solid-state lasers using trivalent rare earth ions are efficient sources in the near- and mid-infrared spectral regions. Their unique properties arise from special energy level structures in different host materials and highly efficient laser operation became possible with the availability of highly efficient high-brightness pump sources like laser diodes. This work will give an overview of quasi-three-level solid-state lasers emitting in the wavelength range 1–5 μm. Recent research and advances in spectroscopic and laser results will be presented. In comparison to four-level lasers such as e.g. Nd3+ lasers at 1.06 μm, quasi-three-level lasers show a much stronger influence of temperature on laser performance, mainly due to the thermally induced changes in the spectroscopic properties of the laser medium. Nevertheless, highly efficient lasers can be realized by direct diode pumping with high spatial and spectral brightness laser diodes. The population dynamics in the manifolds also play an important role and ion concentrations are used to minimize or maximize energy-transfer effects. These general topics will be addressed in Sect. 1, in which basic aspects of quasi-three-level lasers and their description are discussed. Section 2 deals with the general energy-level structure of trivalent rare earths in hosts, from which the most interesting ions and their transitions can be derived. These ions, Nd3+, Yb3+, Er3+, Tm3+ and Ho3+, are investigated in detail in Sect. 3 in order of their emission wavelengths, focusing on their spectral properties and laser results in different laser architectures and host media. In Sect. 4 the work is finally summarized.

Recent Progress and Future Prospects of Advanced High Brightness Diode and Diode Pumped Lasers in the German National BRIOLAS Initiative

High power diode lasers become more and more important, not only as a pumping source for disc and fiber type solid state lasers, but also in direct use e.g. for materials processing, for medical applications and for display technology. Against the background of all these applications increase of brilliance, i.e. enhancement of power and improvement of beam quality and for technical and economic reasons at the same time extension of lifetime and raise of power conversion efficiency are the major goals in activities in research facilities all over the world. Re¬cognizing the importance of optical technologies in general for the German economy a special funding program "Optical Technologies - made in Germany" has been launched by the German Federal Ministry of Education and Research (BMBF) in 2002. In frame of this program technology and applications of diode lasers are intensively studied in the BRIOLAS-initiative.

All-solid-state continuous-wave yellow laser based on intracavity frequency-doubled self-Raman laser action

We report continuous-wave yellow emission from a compact Nd:YVO4 self-Raman laser with intra-cavity frequency-doubling in LBO, pumped by a 4.5 W high-brightness diode laser. A maximum yellow output of 140 mW was observed with an overall optical (diode-to-yellow) conversion efficiency of 4.4%, and with a high beam quality (M2∼1.2). A variety of different resonator configurations were investigated in order to achieve low threshold, highest output powers and efficiency, and to investigate amplitude stability.

Low-threshold and continuously tunable Yb:Gd2SiO5 laser

Yb : Gd 2 Si O 5 (Yb:GSO) exhibits a large fundamental manifold splitting. Its long-wavelength emission band around 1088nm, which has the largest emission cross section, encounters the lowest reabsorption losses caused by thermal population of the terminal laser level. As a result, low-threshold and tunable continuous-wave Yb:GSO lasers were demonstrated. A slope efficiency up to 86% and a pumping threshold as low as 127mW were achieved for a continuous-wave Yb:GSO laser at 1092.5nm under the pump of a high-brightness laser diode. A continuous tunability between 1000 and 1120nm was realized with an SF14 prism as the intracavity tuning element.

A Spectroscopically Resolved Photo- and Electroluminescence Microscopy Technique for the Study of High-Power and High-Brightness Laser Diodes

A novel and advanced characterization technique is described for performing optical studies of the luminescence properties of materials. It was developed for the investigation of semiconductor materials, including semiconductor laser diodes and photonic integrated circuits. A quantitatively calibrated, spatially and spectrally resolved imaging technique is described, which is based upon the technologies of photoluminescence microscopy and photoluminescence spectroscopy. The principles of the spectroscopically resolved photo- and electroluminescence microscopy techniques are outlined in this paper, and the developed instrument is described in detail. Design calculations used to select and set up the experimental apparatus are presented, and results are found to compare well with this analysis. Various experimental measurements are used to demonstrate the performance of the new instrument. The study of strain and defects in high-power laser diodes is presented as one of the more challenging applications of the new technique. The results presented demonstrate the ability of this technique to image photoluminescence shifts occurring in the substrate of packaged laser bars, enabling the investigation of strain, defects and their evolution with aging. Other applications of the technique include the spectroscopic measurement of near- and far-field patterns and virtual sources of laser diodes, investigations of spectral hole burning and optical scattering processes in lasers and photonic integrated circuits, and studies of organic LEDs. In the future, applications are also envisaged in medicine and the biological sciences.

Reliable 1-W CW Operation of High-Brightness Tapered Diode Lasers at 735 nm

The long-term stability of high-brightness diode lasers at 735 nm was investigated. The diodes consist of an index-guided straight section and a gain-guided tapered section. A 1-W continuous-wave operation for 2-mm-long tapered lasers over 3200 h is reported. The experiments demonstrate high reliability with degradation rates below 3.2/spl times/10/sup -5/ h/sup -1/.

Reliable high-efficiency high-brightness laser diode bars at [formula omitted

High-quality InGaAs/AlGaAs laser diode bars emitting at 940 nm have been fabricated by low-pressure metal-organic chemical vapor deposition (LP-MOCVD). Two hundred and ten Watts maximum continuous-wave output power and a maximum power conversion efficiency of 60% at an output power of 72 W have been demonstrated for a single 1-cm-wide laser bar. These bars exhibit a very good beam quality of 5.7°×27.2° (full-width at half-maximum). Reliability test have been carried out for over 2000 h at ∼58 W at room temperature. Under these conditions, the extrapolated lifetime is ∼100,000 h , which suggests that AlGaAs-based lasers of proper designs could have similar long-term reliability as their Al-free counterpart.

High-brightness diode lasers

The basic concepts and some modelling aspects of high-brightness semiconductor lasers are reviewed. The technology of lasers with a tapered gain-region is described. They provide the highest brightness of a semiconductor source with continuous wave emission in the visible and near infrared spectral range. Experimental results are presented for tapered lasers emitting at 735 nm and 808 nm. Output powers of 3 W were achieved in nearly diffraction limited beams. To cite this article: H. Wenzel et al., C. R. Physique 4 (2003).

Design optimisation for high-power high-brightness parabolic bow-tie laser diodes

Optical sources that combine high power with high brightness are in great demand for various applications. Although sophisticated device designs have been demonstrated to have such desirable characteristics, to contain the device costs tapered geometry devices seem to provide attractive alternatives. Further, particularly for high-power operation, the bow-tie configuration is effective for further reducing the risk of catastrophic optical damage and for obtaining a good quality output beam. The authors present the detailed analysis that has been necessary to optimise both the material layer structure and the tapered laser geometry to achieve simultaneously high power and high brightness. Following the design guidelines, several 980 nm parabolic bow-tie lasers have been fabricated and characterised in-house, obtaining output powers in excess of 700 mW per facet in a diffraction-limited (2.7°) beam measured without the use of external lenses.

Passively mode-locked Yb:KYWlaser pumped by a tapered diode laser

We demonstrate the operation of a low threshold femtosecond Yb:KYW laser, using a saturable absorber mirror for passive mode-locking and a high brightness laser diode as pumping source. Fourier-limited pulses with a duration of 101 fs are achieved at an output power of 100 mW. The performance of the Yb:KYW laser was also compared to that of Yb:KGW.

Passively mode-locked diode-pumped surface-emitting semiconductor laser

A surface-emitting semiconductor laser has been passively mode locked in an external cavity incorporating a semiconductor saturable absorber mirror. The gain medium consists of a stack of 12 InGaAs-GaAs strained quantum wells, grown above a Bragg mirror structure, and pumped optically by a high-brightness diode laser. The mode-locked laser emits pulses of 22-ps full-width at half maximum duration at 1030 nm, with a repetition rate variable around 4.4 GHz.

Diode-pumped femtosecond Yb:KGd(WO_4)_2 laser with 11-W average power

We demonstrate what is to our knowledge the first mode-locked Yb:KGd(WO(4))(2) laser. Using a semiconductor saturable-absorber mirror for passive mode locking, we obtain pulses of 176-fs duration with an average power of 1.1 W and a peak power of 64 kW at a center wavelength of 1037 nm. We achieve pulses as short as 112 fs at a lower output power. The laser is based on a standard delta cavity and pumped by two high-brightness laser diodes, making the whole system very simple and compact. Tuning the laser by means of a knife-edge results in mode-locked pulses within a wavelength range from 1032 to 1054 nm. In cw operation, we achieve output powers as high as 1.3 W.

Scaling of longitudinally diode-pumped self-frequency-doubling Nd:YCOB lasers

We report the scaling of a new self-frequency-doubling laser, based on the crystal Nd/sup 3+/:YCa/sub 4/O(BO/sub 3/)/sub 3/, to higher powers. The power scaling is achieved by diode pumping using a novel technology of combining the output of up to four high-brightness laser diodes. Spectroscopic, thermo-mechanical, and laser properties are investigated for use in designing high-power self-frequency-doubling lasers. Using a method of angular-multiplexing individual laser diodes for pumping, we demonstrate output powers of more than 1.9 W of fundamental (1060 nm) radiation and 245 mW at the second harmonic. Experimental investigation rendered a thermal stress resistance figure-of-merit for this material to be between 210-280 W/m.

Développement de lasers visibles pompés par diode à base de cristaux de Nd [formula omitted]GdCOB autodoubleurs de fréquence

We present the performances of a diode-pumped solid-state laser operating in the visible by self-frequency-doubling. A cw output power of 115 mW at 545 nm has been obtained in a stable concave–concave cavity by using a crystal of Nd:GdCa 4O(BO 3) 3 pumped by a 2 W high-brightness laser diode. In a plano–plano cavity, similar to a microchip laser, we have obtained, for the first time to our knowledge, an output power of 22 mW in the green.

Overview of the laser and non-linear optical properties of calcium-gadolinium-oxo-borate Ca 4GdO(BO 3) 3

Ca 4GdO(BO 3) 3 (GdCOB) is a new non-linear optical (NLO) material which presents a congruent melting and can be grown from the melt in large size crystals ( φ=50 mm, L=120 mm) using the Czochralski pulling method. This paper describes the crystal growth and NLO properties of GdCOB which compare favorably with those of commercial borates like BBO or LBO. Particular emphasis will be put on SHG of the Nd:YAG 1.064 μm laser emission. Large amounts of Nd or Yb ions can be substituted for Gd in this material and Ln:GdCOB with Ln=Nd, Yb exhibits interesting laser properties, especially in the case of diode pumped Yb activated crystals. Finally by combining the NLO properties of the GdCOB matrix and the laser emission associated with the active ion, a green self frequency-doubling laser is obtained. In this field, Nd:GdCOB appears the most promising material for practical applications, able to generate visible green laser light with only one single crystal instead of two, as usually. To date an Nd:GdCOB crystal yields 114 mW at 530.5 nm (for 1250 mW of absorbed pump power), when pumped with a 2 W high brightness laser diode.

Diode-pumped Nd:S-VAP lasers passively Q-switched with Cr 4+:YAG saturable absorber

A compact diode-pumped passively Q-switched Nd:S-VAP laser has been demonstrated with Cr 4+:YAG crystal as the saturable absorber. When CW pumped with a 1 W high-brightness laser diode, stable laser pulses of duration of 2.9 ns and energy of 13.7 μJ are observed with kilohertz repetition rates. The highest peak power of 4.6 kW was obtained at a incident pump power of 904 mW.

25-W CW high-brightness tapered semiconductor laser-array

High-power high-brightness laser diode arrays comprising 25 tapered laser oscillators have been fabricated. The devices, based on recently developed low-modal gain epitaxial layer-structures, deliver a maximum output power of more than 25-W continuous-wave. A high beam quality uniformity is achieved with an average beam quality factor of M/sup 2/=2.6 for each individual emitter. Compared to conventional broad-area laser diode arrays the brightness of each emitter is improved by more than an order of magnitude in the slow-axis direction. These arrays have the potential to produce optical power densities as high as 1 MW/cm/sup 2/.