Blue Second Harmonic Generation Research Articles

Upconversion emission and second harmonic generation of the YVO4: Tm3+, Er3+, Yb3+ inverse opals

The YVO4:Tm3+, Er3+, Yb3+ nanomaterials were fabricated with a simple chemical method. The X-ray diffraction, scanning electron microscopy and transmission electron microscopy characterizations confirm that the YVO4:Tm3+, Er3+, Yb3+ nanomaterials have good structure with the polycrystalline. With the excitation of the 975 nm laser, the white color emissions were observed in the YVO4:Tm3+, Er3+, Yb3+ inverse opals with the polystyrene (PS) size of 450 nm and the composition of Y:Tm:Er:Yb = 77.5:0.5:2:20, in which the blue emission is the second harmonic generation (SHG) signal of the incident laser. The inverse opals have great effect on the upconversion emission and the SHG signal. With the inverse opal structures the blue SHG signal increases significantly for the inverse opals with the PS size of 250 and 450 nm, in which the SHG signal of the inverse opal with the PS size of 450 nm is stronger and is more suitable for the white emission due to the narrow width of the SHG signal. The power dependencies confirm that the upconversion emissions have the slope factor of 2–3, which means that the upconversion processes are the three-photon processes.

Highly efficient continuous wave blue second-harmonic generation in fs-laser written periodically poled Rb:KTiOPO_4 waveguides

Waveguides were inscribed into a 9.5 mm long periodically poled KTiOPO4 crystal with a Ti:sapphire femtosecond-laser. Waveguiding was achieved between two parallel written tracks with spacings of 17-19 μm. The fundamental power of 1.6 W for frequency doubling in the waveguide was delivered by a continuous wave Ti:sapphire laser at a wavelength of 943.18 nm. A maximum output power of 76 mW in the blue spectral region was achieved. This corresponds to a single pass normalized conversion efficiency of 4.6% W(-1) cm(-2).

Temperature dependent blue second harmonic generation in Ba5Li2Ti2Nb8O30 microcrystals embedded in TeO2 glass–matrix

Abstract The as-quenched samples in the system (100 − x ) TeO 2 -( x ) Ba 5 Li 2 Ti 2 Nb 8 O 30 (2 ⩽ x ⩽ 8) were found to be embedded with 10–20 μm sized crystallites of the polar phase Ba 5 Li 2 Ti 2 Nb 8 O 30 (BLTN). Blue (400 nm) second harmonic generation (SHG) was observed in transmission mode when 800 nm laser light was allowed to pass through the individual crystallites. The blue SHG signal was temperature dependent and its intensity was maximum at ∼175 °C which was tentatively attributed to the concomitant changes associated with the refractive indices of the BLTN crystallites. The SHG intensity attained a minimum value around the Curie temperature of BLTN crystals.

Ultraviolet Second-Harmonic Generation and Sum-Frequency Mixing in Two-Dimensional Nonlinear Optical Polymer Photonic Crystals

Second-harmonic generation (SHG) and sum-frequency mixing (SFM) are investigated in a two-dimensional photonic crystal (PhC) waveguide formed using a nonlinear optical (NLO) polymer with metallic cladding. The improved waveguide structure of the NLO polymer PhC enables the realization of ultraviolet and blue SHG and SFM radiation at wavelengths ranging from 368 to 400 nm. Large SHG enhancement at 368 nm was observed, originating from resonance between the external pump laser field and a photonic band mode. The SHG enhancement results agree well with the experimental photonic band structure obtained by angle-dependent optical reflectivity and the theoretical structure generated by three-dimensional finite-difference time-domain calculations.

Type I quasi-phase-matched blue second harmonic generation with different polarizations in periodically poled LiNbO 3

First-order type I quasi-phase-matched (QPM) E Y ω + E Y ω → E Z 2 ω blue second-harmonic generation was demonstrated in periodically poled LiNbO 3 with period of 14.5 μm using d 31. 52 μJ of harmonic blue light at 0.473 μm was generated pumped by 114 μJ 35 ps pulse laser at 0.946 μm at 150 °C with a conversion efficiency of 45.6%. The average conversion efficiencies of 41.3% and 19% were also obtained at 150 °C, respectively, in the conventional first- and third-order QPM E Z ω + E Z ω → E Z 2 ω blue second-harmonic generation at 0.473 μm. The temperature acceptance bandwidths of 20 mm length periodically poled LiNbO 3 with first-order grating periods of 14.5 and 4.5 μm are 2.0 and 0.9 °C, respectively. The larger acceptance bandwidths and grating period for E Y ω + E Y ω → E Z 2 ω than those for E Z ω + E Z ω → E Z 2 ω enhance the frequency conversion efficiency, which shows the polarization dependence of quasi-phase matching.

A Practical Laser Projector with New Illumination Optics for Reduction of Speckle Noise

We have developed illumination optics for image projection systems. It realizes uniform illumination and suppression of speckle and diffraction noises by using a diffuser and integrator optics. By optimizing the diffusing angle of the diffuser, optical power loss was less than 10%. A proto type of a laser projector with a red wide-stripe semiconductor laser and green and blue second-harmonic generation lasers was realized by using the developed illumination optics and twisted nematic liquid-crystal panels. Still images from a personal computer and video images from a digital versatile disk (DVD) player were displayed with the system and a wide colour gamut and smooth images without diffraction noise nor speckle noise were confirmed.

Blue and Ultra-Violet Radiations Using Quasi-Phase-Matched Second Harmonic Generation Devices

Quasi-phase matched (QPM) second-harmonic generation (SHG) device offers various application for blue and ultra-violet (UV) radiations. Advanced poling technology made it possible to realize micron and sub-micron poling geometry in efficient nonlinear materials. Using these techniques, first-order nonlinear gratings have been realized for high power blue and UV SHG. Based on these devices, high power short wavelength laser sources were demonstrated for practical use. Recent progress in this area is reviewed with emphasis on research work of the author's group using bulk and waveguide QPM devices.

Low‐noise blue light generation of intracavity frequency‐doubled LD‐pumped Cr:LiSAF laser by single‐mode method

AbstractWe have demonstrated the production of low‐noise blue SHG (Second Harmonic Generation) light by single‐mode oscillation in an intracavity frequency‐doubled laser diode (LD)‐pumped Cr‐doped LiSrAlF6 (Cr:LiSAF) solid‐state laser. The SHG crystal was LiB3O5 (LBO). A birefringent filter and an etalon plate were used for the single‐mode Cr:LiSAF laser oscillation wave. A maximum blue SHG output power of 32 mW was obtained by using a 1‐mm‐thick birefringent filter and an etalon plate 200 μm thick with 20% reflectivity. The oscillation wavelength varied by 0.24 pm/hPa in response to changes in atmospheric pressure. A long‐term stability of 300 hours was obtained with the cavity enclosed in a barostat. © 2001 Scripta Technica, Electr Eng Jpn, 138(1): 49–55, 2002

Nonlinear optical properties of poly[(4′-acetylphenylaminoformyloxy- 4-styrene)-co-(4-hydroxystyrene)] and guided mode-mode second-harmonic generation in waveguide

Linear and nonlinear optical properties of electrically poled films of newly synthesized poly [(4′-acetylphenylaminoformyloxy-4-styrene)-co-(4-hydroxystyrene)] [poly(AS-co-HS)] are investigated. Linear optical properties of a poly(AS-co-HS) film are measured by the prism-coupling method. Ultraviolet (UV) transparency down to 350 nm identifies that this polymer is a promising candidate for second-harmonic generation (SHG) in the UV-visible light region. Corona-poling technique is used to produce a noncentrosymmetric structure. The induced d33 at λ=1064 nm is 2.8 pm/V. High glass-transition temperature (Tg=160 °C) results in very long decay time of the nonlinearity, d33. The decay time at operating temperature of 80 °C is estimated to be more than ten years. Guided-mode blue and green SHGs are demonstrated using the film as a slab waveguide.

単一モードによる低ノイズ青色発生LD励起Cr:LiSAF-SHGレーザ

We demonstrated low noise blue SHG (Second Harmonic Generation) light by a single mode oscillation for intracavity frequency doubled laser diode (LD) pumped Cr dope LiSrAlF6 (Cr:LiSAF) solid state laser. The SHG crystal used LiB3O5 (LBO). A birefringent filter and an etalon plate were used for single mode of Cr:LiSAF laser oscillation wave. The maximum blue SHG output power obtained 32 mW by using 1mm thickness of birefringent filter and 20% reflectivity 200 μm thickness of an etalon plate. The oscillation wavelength is changed with 0.24 pm/hPa for atmospheric pressure. The long term stability showed 300 hours by the cavity inserted into pressure box.

31%-efficient blue second-harmonic generation in a periodically poled MgO:LiNbO_3 waveguide by frequency doubling of an AlGaAs laser diode

We present a method of controlling the shape of the domain-inverted structure in an off-cut MgO:LiNbO(3) crystal by utilizing a two-dimensional high-voltage application. With this technique a periodically domain-inverted structure with a period of 3.2 microm and a thickness of 2.0 microm was fabricated over a 10-mm interaction length. This structure has made possible sufficient overlaps between propagation modes and domain inversion in the waveguide. Using this structure, we demonstrated cw blue second-harmonic generation of 17.3 mW of power at a wavelength of 426 nm with single-pass 55-mW cw AlGaAs laser diode input, which corresponded to 31% power-conversion efficiency.

Cerenkov-radiation and guided-mode blue second-harmonic generation in four-layer waveguides using organic thin-film crystals

Four-layer waveguide devices for second-harmonic generation were investigated by use of a new organic nonlinear optical crystal, isopropyl-4-acetylphenylurea. Blue second-harmonic generation in the form of the Cerenkov-radiation mode and the guided mode (from TE0ω to TE12ω) was demonstrated with a thin-film crystal of isopropyl-4-acetylphenylurea as a substrate. For the relaxation of the phase-matching condition and improvements in conversion efficiency, the thickness-noncritical phase-matching technique was introduced in the organic–inorganic hybrid four-layer waveguide geometry.

Organic crystal isopropyl-4-acetylphenylurea and waveguide second-harmonic generation

A new organic crystal isopropyl-4-acetylphenylurea (IAPU) was identified as a promising candidate for blue second-harmonic generation (SHG). The nonlinear optical d coefficient obtained is d22=30.5 pm/V at the fundamental wavelength 1064 nm, and the crystal's transmitting range is 380–1400 nm. Thin, single crystalline films fabricated on the glass substrate are useful for waveguide-device applications. For the improvement of SHG efficiency and the relaxation of phase-matching conditions, the concept of thickness-noncritical phase matching (TNCPM) in a four-layer waveguide is proposed. Modal dispersion calculations for the various four-layer structures suggested the possibility of TNCPM from the TE0ω mode to TE12ω mode and from the TE0ω mode to the TE22ω mode by adjustment of the refractive indices of the two guiding layers.

Recent progress of organic nonlinear optics in Japan

In the field of nonlinear optics (NLO), the organic materials are relative newcomers compared to inorganic single crystals and semiconductors. In this paper, we give a review on the recent progress of organic NLO in Japan. This includes: (1) molecular design strategies, (2) thin-film forming techniques, (3) phase-matching methods, (4) single crystals for blue second-harmonic generation, (5) electro-optic polymers. We show a number of achievements on organic NLO that have been obtained in Japan; further studies should be done to realize practical applications of organic NLO.

Growth and characterization of K3Li2(TaxNb1−x)5O15 crystals for blue second-harmonic-generation applications

Potassium lithium tantalate niobate, K3Li2(TaxNb1−x)5O15, or KLTN single crystals were grown by spontaneous crystallization method, and it has been demonstrated that the KLTN crystal has high potential as a nonlinear crystal for blue second-harmonic-generation (SHG) applications. Ta substitution for Nb site in K3Li2Nb5O15 crystal improves the transparency in the blue light region and decolorizes the material. Compared with K3Li2Nb5O15, the K3Li2Ta5O15 crystal exhibits a 60 nm blueshift of the absorption edge from 376 to 316 nm, and decreases its absorption coefficient from 2.3 to 0.3 cm−1 at 400 nm. The phase-matched frequency doubling of the Ti:sapphire infrared laser for blue SHG at room temperature has been demonstrated with the KLTN bulk crystal.

Blue second-harmonic generation in waveguides fabricated in undoped and scandium-doped KTiOPO4

The efficiency of second-harmonic generation at 425 nm has been measured in periodically segmented waveguides in undoped and 120 ppm Sc3+-doped c-axis-oriented KTiOPO4 (KTP) plates. Conversion efficiencies up to 200% and 325%/W cm2 are obtained for the two types of crystals. These efficiencies are found to have decreased by up to a factor of 2 after the generation of 2–4 mW of cw blue output power for more than 5 min, while the transmission of the pump beam is decreased by about 20%. These effects are semipermanent in undoped KTP, and are therefore ascribed to optical damage. A full recovery within a few minutes is, however, found in the Sc3+-doped KTP waveguides. The ionic conductivity along the polar axis of 120 ppm Sc3+-doped KTP has been measured to be about equal to that of undoped KTP, so that the difference in the optical damage characteristics of the waveguides is not caused by a difference in the conductivity of the substrate KTP. The conductivity of 230 ppm doped crystals is found to be about a factor of 30 lower than that of undoped KTP, and has a different dependence on current frequency. In these crystals domain inversion in the exchanged waveguide segments was not obtained.

Preparation and characterization of organic thin film for semiconductor laser frequency doubling

Organic non-linear optical (NLO) materials hold the promise of realizing blue, second harmonic generation (SHG) semiconductor lasers, which have versatile applications due to their large nonlinearities. Among the organic NLO materials known today, conjugated benzene derivative compounds, which have been studied most extensively, have the largest non-linear effects. At the same time, they often have large birefringences and a red-shifted cut-off (>500 nm). These shortcomings have significantly influenced their applications in frequency doubling. 3-Methoxy-4-hydroxy-benzaldehyde (MHBA), grown in our laboratory, is an excellent organic NLO material. Its cut-off is at 375 nm, but it still has large NLO coefficients and relatively small birefringences [1,2]. Even so, MHBA still cannot realize non-critical phase matching (NCPM) in the spectral region of the GaA1As series laser, which is an important factor influencing the blue SHG of lower power laser diodes. Recently, SHG in an organic single-crystalline optical waveguide demonstrated new potentials in laser diode frequency doubling [3, 4]. In this letter, we describe the growth and characterization of MHBA single-crystalline film. MHBA single-cryStalline film was prepared by the Bridgman method. Before film growth, two polished fused quartz substrates (20 x 30mm) were thoroughly cleaned. The paired substrates were dipped into the MHBA melt in a glass tube controlled at a temperature of 95 °C (compared with its melting point of 83 °C). Capillary action ensured that the melt could penetrate into the gap between the two substrates. When the temperature cooled to room temperature the film in the gap was composed of randomly oriented small crystals. After melt penetration, the film inside the substrates was recrystallized to make a large-area single-crystalline film, using the apparatus shown in Fig. 1. The MHBA polycrystalline film inside the paired substrates was suspended and lowered through the growth region in a stove at a motor-controlled rate of 0.3 mmh -1 for recrystallization. In our experiments, the largest area of the grown film was up to 10 x 10 ram. The quality of the prepared film depended on several factors: the cleaning and polishing of the substrates, the temperature distribution in the stove, the stability of the whole growth apparatus, the down speed of the substrates and the purity of raw materials.

High power blue light generation by frequency doubling of a laser diode in a periodically domain-inverted LiTaO3 waveguide

We report high power and stable blue-light generation by frequency doubling a laser diode, stabilized by a grating feedback technique, in a periodically domain-inverted LiTaO3 waveguide. Due to the deep domain-inverted regions and strong waveguide confinement formed by proton-exchange and a quick heat treatment, high efficiency second harmonic generation (SHG) has been obtained. Locking the oscillation wavelength of a laser diode through the waveguide by a grating feedback technique, 8 mW of stable blue SHG has been demonstrated.

First-order quasi-phase matched LiNbO3 waveguide periodically poled by applying an external field for efficient blue second-harmonic generation

A novel method of fabricating a periodic domain structure with ideal laminar domains in LiNbO3 by applying an external field at room temperature is proposed. The method allows a high blue beam power of 20.7 mW and a high conversion efficiency of 600%/W cm2 to be obtained.

Stable blue second-harmonic generation in a KTP waveguide with a diode laser in an external cavity

Stable second-harmonic generation from a diode laser, using a quasi-phasematching KTP waveguide and a grating in an external cavity is described. 1.35 mW of blue light was generated and the power fluctuation was less than 0.3%.