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We report on the generation of 550 mW of 460 nm blue radiation by single pass frequency doubling the picosecond pulses of a mode-locked InGaAs diode laser MOPA system in periodically poled KTP.Compact blue laser sources are of interest for many applications such as optical data storage, medical diagnostics, lithography and display technology. Although the operation of blue semiconductor diode lasers has recently been demonstrated [1] the development of reliable high power devices as required for most applications still remains a challenge. Today the blue output of commercially available GaN diode lasers is usually less than 30 mW.An alternative concept for diode laser based blue light sources is the second harmonic generation (SHG) of near infrared diode laser radiation [2]. Appropriate diode laser sources are master oscillator power amplifier (MOPA) systems based on amplifiers with a tapered lateral geometry of the active area. Such devices provide output powers of more than 5 W in a near-diffraction-limited beam [3]. An attractive method for increasing the conversion efficiency is the use mode-locked ultrashort pulses [4]. Because of the high pulse power high SHG efficiencies are achievable in a single pass through periodically poled nonlinear crystals [5]. This concept is much simpler and provides high long-term stability compared e.g. to SHG in external high finesse enhancement cavities [6].In this paper we report on the generation of 550 mW of blue light at 460 nm by single pass frequency doubling of picosecond pulses generated by an InGaAs diode laser MOPA-system in periodically poled KTiOPO3 (KTP). To our knowledge this is the highest average power generated by frequency doubling diode laser radiation without using a resonant enhancement cavity. Fig. 1 Scheme of the experimental setup a828_1.pdf CFG6.pdf 1-55752-813-6/06/$25.00 ©2006 IEEE

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This letter reports on broadband laser sources based on InGaAs tapered diode laser amplifiers with external optical feedback. The generated 920nm radiation with a bandwidth of up to 20nm and a power of a few hundred milliwatts is emitted in an almost diffraction limited beam. Spectral filtering and subsequent amplification in a second tapered amplifier provides radiation with spectral widths in the range of 20to40nm and optical output powers of up to 2.5W.

A scheme for the generation of modulated blue laser radiation is demonstrated. The 923nm radiation of a high-power diode-laser master-oscillator power-amplifier system is wavelength modulated within a range of 0.2nm by modulating the injection current of the distributed feedback (DFB) diode oscillator. Single-pass frequency doubling of the generated radiation in periodically poled potassium titanyl phospate converts the wavelength modulation into an intensity modulation with a contrast ratio exceeding 700:1. The 3dB modulation bandwidth of 35kHz is limited by the speed of the wavelength tuning of the DFB oscillator.