Internal Second Harmonic Generation Research Articles

Second harmonic generation in gallium phosphide nano-waveguides.

We designed, fabricated and tested gallium phosphide (GaP) nano-waveguides for second harmonic generation (SHG). We demonstrate SHG in the visible range around 655 nm using modal phase matching. We observe phase matched SHG for different combinations of interacting modes by varying the widths of the waveguides and tuning the wavelength of the pump. We achieved a normalized internal SHG conversion efficiency of 0.4% W-1cm-2 for a continuous-wave pump at wavelength of 1283.5 nm, the highest reported in the literature for a GaP waveguide. We also demonstrated temperature tuning of the SHG wavelength with a slope of 0.17 nm/°C. The presented results contribute to the development of integrated photonic platforms with efficient nonlinear wave-mixing processes for classical and quantum applications.

Femtosecond superradiance in semiconductor lasers: anomalous internal second-harmonic generation

The emission of anomalously bright blue light under internal doubling of the frequency of femtosecond superradiance pulses in the active medium of semiconductor GaAs/AlGaAs laser heterostructures has been experimentally found. The efficiency of the internal second-harmonic generation is an order of magnitude higher than in the conventional lasing regime. This effect is due to the formation of a transient ordered state of electrons and holes under superradiance, occurrence of dynamic coherent population lattices, and periodic modulation of the nonlinear susceptibility of the medium.

Continuous-wave, single-frequency, solid-state blue source for the 425–489 nm spectral range

We report a new source of cw, single-frequency radiation in the blue, offering extended tunability and practical powers in a compact, all-solid-state design. The device is based on a green-pumped, cw, singly resonant optical parametric oscillator using MgO-doped stoichiometric lithium tantalate (MgO:sPPLT) as the nonlinear material. By internal second-harmonic generation of the resonant near-infrared signal radiation in a 5 mm BiB(3)O(6) crystal, we generate nearly 450 mW of cw, single-frequency blue power over a tunable range of 425-489 nm with a linewidth of 8.5 MHz and a Gaussian spatial beam profile. The demonstrated wavelength coverage can be further extended by using alternative gratings for the MgO:sPPLT crystal.

Efficient continuous wave second harmonic generation pumped at 1.55 µm in quasi-phase-matched AlGaAs waveguides

We have fabricated quasi-phase-matched AlGaAs waveguides for continuous-wave second-harmonic generation (SHG) pumped around 1.55 microm. We find that the losses, which limit the conversion efficiency of this type of waveguide, are resulted from two corrugations--the initial template corrugation and the regrowth-induced domain-boundary corrugations. We are able to reduce the waveguide loss by improving the growth conditions. The waveguide loss is 6-7 dB/cm at 1.55 microm, measured using the Fabry-Perot method. A record internal SHG conversion efficiency of 23 %W-1 for AlGaAs waveguides is achieved using a 5-mm-long waveguide with a pump wavelength of 1.568 microm.

Highly efficient blue-light generation from a compact, diode-pumped femtosecond laser by use of a periodically poled KTP waveguide crystal.

We present a simplified, potentially portable, and highly efficient blue-light source from a periodically poled KTP waveguide crystal with a compact femtosecond Cr:LiSAF laser. This light source generates 5.6 mW of blue average output power at 424 nm with 27 mW of incident fundamental in a single-pass extracavity arrangement at room temperature. The overall system efficiency of electrical power to blue light is 0.5%, and the internal second-harmonic generation conversion efficiency is as high as 37%. The slope efficiency of 5.5% pJ(-1) at low pulse energies is, to our knowledge, the highest slope efficiency yet reported for frequency conversion into the blue spectral region.

Measurement of the nonlinear coefficient of orientation-patterned GaAs and demonstration of highly efficient second-harmonic generation

Quasi-phase-matched (QPM) GaAs structures, 0.5 mm thick, 10 mm long, and with 61-mum grating periods, were grown by a combination of molecular-beam epitaxy and hydride vapor phase epitaxy. These were characterized by use of mid-IR second-harmonic generation (SHG) with a ZnGeP(2) (ZGP) optical parametric oscillator as a pump source. The SHG efficiencies of QPM GaAs and QPM LiNbO(3) were directly compared, and a ratio of nonlinear coefficients d(14)(GaAs)/d(33) (LiNbO(3))=5.01+/-0.3 was found at 4.1-mum fundamental wavelength. For input pulse energies as low as 50muJ and approximately 60-ns pulse duration, an internal SHG conversion efficiency of 33% was measured in QPM GaAs.

Letter Phase-mismatching effects in the internal second-harmonic generation in InGaAs quantum-well laser diodes

Abstract We have characterized the role of phase-mismatching in the spectral distribution of the internal second-harmonic generation (ISHG) in the CW operation of high-power InGaAs quantum-well laser diodes emitting at around 960 nm. The observed pairs of narrow blue-green peaks of ISHG have symmetrical spectral positions with respect to the central peak of the pure second harmonic at ∼480 nm, suggesting that their generation in the laser waveguide is most probably mediated by a mechanism of reciprocal cancellation of the respective phase-mismatch vectors. The relatively strong emission of the ISHG radiation at the output mirror facet indicates that this second-order nonlinear optical process is enhanced by waveguiding in the laser active region.

Letter Phase-mismatching effects in the internal second-harmonic generation in InGaAs quantum-well laser diodes

We have characterized the role of phase-mismatching in the spectral distribution of the internal second-harmonic generation (ISHG) in the CW operation of high-power InGaAs quantum-well laser diodes emitting at around 960 nm. The observed pairs of narrow blue-green peaks of ISHG have symmetrical spectral positions with respect to the central peak of the pure second harmonic at ∼480 nm, suggesting that their generation in the laser waveguide is most probably mediated by a mechanism of reciprocal cancellation of the respective phase-mismatch vectors. The relatively strong emission of the ISHG radiation at the output mirror facet indicates that this second-order nonlinear optical process is enhanced by waveguiding in the laser active region.

Characterisation of III–V optoelectronic devices by Internal Second-Harmonic Generation technique

A surface characterization technique based on the Internal Second-Harmonic Generation (SHG) in optoelectronic devices has been used to study the mirror degradation of 1.55 μm semiconductor optical amplifiers (SOAs) exposed to an antireflection coating deposition technique and 980 nm pump lasers suffering from mirror oxidation during life-tests. In both cases, an overall increase in SH emission was observed, as a consequence of mechanical stress enhancement and defects formation due to oxidation phenomena occurring at the interface between semiconductor and coating film. In the case of pump lasers, an oscillating, periodic trend superimposed to the general increasing one was also observed and interpreted as the periodic relaxation of compressive strain in the active layer due to vacancies formation in the near-mirror semiconductor layer.

Influence of KTP length on the performance intracavity frequency doubled diode-pumped Nd:YVO4 lasers

We demonstrate an experimental study of the influence of potassium titanyl phosphate (KTP) length on the performance of intracavity frequency-doubled diode-pumped Nd:YVO/sub 4/ lasers operating in continuous-wave (CW) mode and passive Q-switch mode. Theoretical and experimental results show that the optimum KTP length for CW mode is determined by the nonlinear coupling and walkoff effect and the highest optical conversion efficiency in CW mode is nearly 30% with a 10-mm KTP. On the other hand, a 2-mm KTP crystal, which is sufficient for efficient internal second-harmonic generation in a passive Q-switch mode, yield the highest peak green power of 240-W.

High performance AlGaAs-based laser diodes: Fabrication, characterization and applications

Data are presented on high performance AlGsAs/GaAs and InGaAs/AlGaAs quantum well laser diodes fabricated by low temperature liquid phase mesa melt-etching and regrowth. The base laser structures were grown either by molecular beam epitaxy or metal-organic vapour phase epitaxy MOVPE. Native oxides were used as a mask in the melt-etching and regrowth processes. Cylindrical microlenses were used for obtaining equal divergence angles in both planes, perpendicular and parallel to the active layer plane at more than 1 W of continuous wave operation optical power. Characterization of mirror catastrophical degradation of single mode laser diodes using traditional electrooptical parameters as well as the parameters of internal second-harmonic generation and measurements of excess mirror temperature were performed. The thermal resistance, active layer mirror temperature and spectral width have been determined as well.

Laser-excited fluorescence of perylene by using self-induced second-harmonic and sum-frequency radiation emanating from high-power AlGaAs double hetero-type diodes

High-power (12 W) pulse-operated AlGaAs double-heterostructure lasers with a large thickness of the active layer (1.5 µm) are able to produce internal second-harmonic and sum-frequency generation with a peak power of 10 mW. The corresponding portion of the electroluminescence spectra has a maximum at 405 nm. Clearly resolved mode structures of the fundamental and harmonic radiation are analysed in detail. Particular transverse modes exhibit different conversion efficiencies. Violet resonances without modal precursors in the infrared spectrum make a marked contribution to the light intensity. The harmonic signal serves as an excitation source in photoluminescence studies. A technique of single-photon counting is applied in order to perform spectral measurements under weak-intensity levels. Bright fluorescence spectra of saturated solution of perylene ino-xylene are presented. The spectrum obtained when the solution is illuminated with a gas discharge lamp shows no differences with respect to the positions of the intensity peaks. This allows us to suggest that AlGaAs high-power lasers can be used as convenient excitation sources in photophysics, in particular in time-resolved experiments.

Fabrication, characterization, and applications of high‐performance AlGaAs‐based buried‐heterostructure diode lasers

Data are presented on buried-heterostructure (BH) AlGaAs/ GaAs and InGaAs/AlGaAs quantum-well diode lasers (DLs) fabricated by low-temperature liquid phase mesa melt etching and regrowth. The basic laser structures were grown by either molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD). Native ox- ides were used as a mask in the processes of melt etching and regrowth. Measurements of excess mirror temperature and parameters of internal second-harmonic generation (SHG) were used for DL characterization. The equalization of beam divergence in both planes, perpendicular and parallel to the active layer, was accomplished by using cylindrical micro- lenses, a t1Wo fradiant power in continuous-wave (cw) operation. The results on medical applications and pumping Er 31 -doped YAG crystals are reported. © 1996 Society of Photo-Optical Instrumentation Engi- neers. Subject terms: diode laser characterization; technological and medical applica- tions of diode lasers.

Internal second-harmonic generation in CW AlGaAs SQW lasers: the facet degradation monitoring

The spectra of the second-harmonic (SH) radiation, generated in the separate-confinement single quantum well (SQW) semiconductor AlGaAs/GaAs laser have been measured at various levels of the injection current. The observed correlation between laser and SH mode intensities is explained by taking into consideration the dispersion of the second-order nonlinear susceptibility of the GaAs active region. It is shown, that due to the high sensitivity of the SH signal to the semiconductor near-surface layer condition, the internal SH generation can be used for the in situ diagnostics of the laser facet degradation processes.

Stabilization of a Mode-Locked Nd: Glass Laser by Intracavity Second-Harmonic Generation

Abstract A method is described for generating stabilized, intensity-limited pulsetrains from a mode-locked Nd:glass laser with internal second-harmonic generation.

Limitations for mode-locking enhancement of internal SHG in a laser

Theoretical expressions are given for the enhancement of second-harmonic generation (SHG) that can be expected from mode-locking in the case of intracavity frequency doubling.