Demonstration of long-term reliability of a 266-nm, continuous-wave, frequency-quadrupled solid-state laser using beta-BaB(2)O(4)

We report what we believe to be the first operation of more than 1000 h of a 266-nm (cw) frequency-quadrupled solid-state laser with a 100-mW output. We used beta-BaB(2)O(4)(BBO) crystal grown by the Czochralski method to double the green-light (532-nm) wavelength, using an external resonant cavity. The green light was generated with an intracavity frequency-doubled Nd:YVO(4)laser pumped by a 4-W laser diode. When the incident 532-nm power on the external resonant doubler was 500 mW, we generated 100 mW of cw 266-nm radiation with the BBO crystal. The degradation rate seems to be proportional to the strength of the UV optical electric field. We also obtained a relative intensity noise of -130dB/Hz at frequencies of 2 to 10 MHz for 266-nm laser light.     

High-energy Ho:LLF MOPA laser system using a top-hat pump profile for the amplifier stage

Numerical simulations show the advantage of using a top-hat intensity profile pumping the amplifier stage in an Ho:LuLiF₄ (Ho:LLF) master oscillator power amplifier (MOPA) configuration over a Gaussian pump profile: higher pulse energies could be generated simultaneously with reduced peak fluence in Q-switched operation. In the experimental implementation, the top-hat beam was realized with a coherent beam transformation of the non-absorbed pump beam transmitted by the oscillator to pump the amplifier stage. The Ho:LLF MOPA produced 103.6 mJ at a repetition rate of 100 Hz with a pulse duration of 30 ns at a wavelength of 2053 nm, which corresponds to an optical-to-optical efficiency of 12.9 %. The beam quality was nearly diffraction limited (M ² = 1.03).     

Femtosecond optical parametric oscillator based on periodically poled KTiOPO(4)

We report a femtosecond optical parametric oscillator based on a periodically poled KTiOPO(4) crystal for which quasi-phase matching is achieved with a 24-microm poling period. The singly resonant parametric oscillator, synchronously pumped by a Ti:sapphire laser at a wavelength of 758 nm, generates a signal at 1200 nm and an idler at 2060 nm. The maximum signal power conversion efficiency of the device is 22% with a pump depletion of 69%. We tune the signal wavelength over a 200-nm band by changing the cavity length. In addition, pump wavelength tuning provides output tunability in the 1000-1235-nm range.     

High-repetition-rate, intracavity-pumped KTP OPO at 1572 nm

An efficient, eye-safe, high-repetition-rate, intracavity optical parametric oscillator (IOPO) inside an acousto-optically Q-switched Nd:YVO₄ laser end pumped by a 30-W fiber-coupled diode laser was demonstrated. The pumping, acousto-optically Q-switched Nd:YVO₄ laser gives 3-W average output power at 1064-nm wavelength at 40-kHz repetition rate. An additional separating mirror, x-cut KTP crystal and output coupler highly reflective at 1064-nm and partially transparent at 1572-nm wavelengths form a flat–flat IOPO resonator of 35-mm length. We have achieved 3-ns-duration pulses for 20-mm-long KTP and 4-ns-duration pulses for 30-mm-long KTP, respectively. More than 8-kW-peak-power pulses with an average power of 1.5 W at the signal wavelength for 40-kHz repetition rate were demonstrated. Due to the intracavity spatial cleaning effect, a near diffraction limited signal beam was achieved despite a relatively worse beam quality of the pumping beam. Conversion efficiencies of 50% with respect to Q-switched output at 1064-nm wavelength and 11% with respect to diode pump power were achieved. PACS 42.55.Xi; 42.60.Gd; 42.65.Yj     

High-repetition-rate Nd:YVO4 slab laser with a 1-D top-hat output beam

A high-repetition-rate electro-optic Q-switched Nd:YVO₄ slab laser is demonstrated in this paper. The Nd:YVO₄ slab inside the compact resonator is end-pumped by a 2-bar laser diode stack. The output beam with one dimension (1-D) top-hat intensity distribution at both near field and far field is generated. Continuous wave (CW) output of 13 5 W is obtained under the total pump power of 50 W. At the repetition rate of 40 kHz, the energy per pulse is 0.32 mJ with its pulse width of 26.3 ns. At 20 kHz, we have achieved the maximum pulse energy of 0.56 mJ and 56 kW peak power with 10 ns pulse width.     

Rewritable polarization-encoded multilayer data storage in 2,5-dimethyl-4-(p-nitrophenylazo)anisole doped polymer

We report a rewritable polarization-encoded multilayer data storage method with a polymer film doped with the azo dye DMNPAA (2,5-dimethyl-4-(p-nitrophenylazo)anisole). It is found that under two-photon excitation by a linearly polarized femtosecond laser beam at wavelength 780 nm the optical axis of DMNPAA molecules can be oriented to the perpendicular direction of the beam via a trans-cis-trans isomerization process. As a result, multilayer polarization-encoded optical data storage is demonstrated by recording two letters of a bit spacing of 4 microm in the same region of a given layer. It is shown that erasing and rewriting a particular layer is possible.     

Linear and nonlinear optical properties of Ca3(VO4)2

Single crystals of Ca₃ (VO₄)₂ have been grown by the Czochralski method. The refractive indices show that the crystals are phasematchable between 1.72 μm and 2.94 μm with favourable values for acceptance angle and spectral width of the incident laser beam in the entire phasematching range. The nonlinear optical coefficients have been measured by the Maker fringe method at a fundamental wavelength of 1.064 μm. They are comparable to those of KDP. Thus the crystals are potentially useful for frequency conversion of broadband or tunable laser sources as semiconductor and F-center lasers. They may also be installed in high f-number IR image converters.     

Compact, efficient diode-end-pumped Nd:GdVO4 slab continuous-wave 912-nm laser

A fiber-coupled laser-diode (LD) end-pumped Nd:GdVO₄ slab continuous-wave (CW) 912-nm laser and an LD bar end-pumped Nd:GdVO₄ slab CW 912-nm laser are both demonstrated in this paper. Using the fiber-coupled LD of end-pumped type, a highest CW 912-nm laser output power of 10.17 W is obtained with a high optical-to-optical conversion efficiency of 24.6% and a slope efficiency of 34.5%. The measured M² factors of beam quality in x and y directions are 5.3 and 5.1, respectively. Besides, an LD bar of end-pumped type is used to realize CW 912-nm laser output, which has the advantages of compactness and low cost. When the pump power is 38.8 W, the output power is 8.87 W and the measured M² factors of beam quality in x and y directions are 16 and 1.31, respectively. In order to improve the beam quality of the 912-nm laser at x direction, a new quasi-concentric laser resonator will be designed, and an LD bar end-pumped Nd:GdVO₄ slab high-power CW 912-nm TEM₀₀ laser will be realized in the future.     

A picosecond near-infrared laser source based on a self-seeded optical parametric generator

We report on the design and development of a new type of near-IR laser source. The source comprises of an optical parametric generator (OPG) and a second harmonic generator (SHG) pumped by an 80-MHz, 1064-nm, 7-ps Nd:YVO₄ laser. The OPG is self-seeded with a fraction of its own signal output, which significantly enhances its conversion efficiency. The SHG doubles the frequency of OPG signal to produce a coherent output. The final output beam has a tunable wavelength near 800 nm, an average power of over 1 W, and a pulse duration around 5 ps. The M²-factor of the output beam can reach 1.1 after spatial filtering. With the new laser source, we have successfully demonstrated coherent anti-Stokes Raman scattering microscopy on 1 μm polystyrene beads, which shows that it has the potential to be a substitute for a picosecond optical parametric oscillator in certain microscopy or spectroscopy applications.     

Waveguide properties and optical switching of prism-coupled Au:SiO2 nanocomposite films

In this study, we present theoretical and experimental analyses on the waveguide mode properties of prism-coupled Au:SiO₂ nanocomposite films with the near infrared laser of 1550 nm wavelength where the optical absorption diminished enough for the generation of guided mode. The evolution of guided mode in the nanocomposite waveguide and its propagation properties were also evaluated. As an effective way of utilizing the surface plasmon resonance properties for the application to optical switching devices, we employed an attenuated total internal reflection type optical switch geometry and tested its effectiveness for the absorptive opto-functional materials system using a cross-modulation technique with 532-nm pump and 1550-nm probe beams. The index change probe beam experiences was found to be purely refractive in nature and negative in sign, presumably due to the photo-thermal effect induced in the nanocomposite film by the irradiation of pump beam.     

Violet light generation by frequency doubling of GaAlAs diode laser using a metallo-organic complex crystal ZnCd(SCN)4

Violet 404-nm radiation is generated by type-I single-pass frequency doubling of the output of an GaAlAs diode laser in critically phase-matched ZnCd(SCN)₄ (ZCTC) crystal, a metallo-organic complex crystal. In this paper, its refractive index and second-harmonic generation phase-matching angles are reported. Using a 3-mm-long ZCTC crystal, a diode laser power of 473 mW generated 390 μW of second-harmonic radiation. More recently, 380-nm, 20 μW ultraviolet (UV) radiation is also realized by frequency doubling of the 100 mW output of a continuous-wave Ti:sapphire laser at 760 nm. ZCTC is a promising UV nonlinear optical candidate material for frequency doubling of diode lasers.     

Photothermal techniques with a top-hat beam excitation

A flatly topped circular beam (“top-hat beam”) is employed as the excitation beam for photothermal deflection and surface thermal lens techniques. The Fresnel diffraction model is applied to describe the photothermal signals. The theoretical comparison between a Gaussian beam and a top-hat beam excited photothermal signal amplitudes shows that the use of the top-hat beam excitation improves the measurement sensitivity of the photothermal techniques. Experimental results for both photothermal deflection and surface thermal lens are presented. The potential applications of the top-hat beam excited photothermal techniques are highlighted.     

Optical properties of a new photorecording polymer based on 2,2-difluoro-4-(9-anthracyl)-6-methyl-1,3,2-dioxaborine

The optical properties of a new photorecording polymer based on 2,2-difluoro-4-(9-anthracyl)-6-methyl-1,3,2-dioxaborine have been investigated. This material is found to change its absorption coefficient and refractive index in the visible range under illumination with a wavelength λ = 405.9 nm. This circumstance makes it possible to record static holograms with a spatial frequency up to 2500 lines/mm, a diffraction efficiency above 60%, and a lifetime more than 6 months. A dynamic change in the effective refractive index of this material under 405.9-nm irradiation is found, due to which one can form control optical elements of the light-light type with a modulation frequency up to 50 Hz in it.     

GeSb_2Te_4相变光存储薄膜材料的短波长静态记录特性的研究

研究了单层ＧｅＳｂ２Ｔｅ４真空射频溅射薄膜在４００ｎｍ～８３０ｎｍ区域的吸收、反射光谱和光学常数（ｎ，ｋ），发现ＧｅＳｂ２Ｔｅ４薄膜在４００ｎｍ～６００ｎｍ波长范围内具有较强的吸收。在短波长静态测试仪上测试了ＧｅＳｂ２Ｔｅ４薄膜的光存储记录特性，发现在５１４．５ｎｍ波长用较低功率的激光辐照样品时薄膜在写入前后的反射率变化较大，擦除前后的反射率对比度较低，可通过膜层设计来提高     

Visible and near-infrared optical properties of Nd:CLNGG crystal waveguides formed by proton implantation

A Nd:CLNGG waveguide structure operated at wavelengths of both 632.8 nm and 1539 nm was demonstrated for the first time to our knowledge, which was produced by the 480-keV H~+ion implantation with a dose of 1.0×10~(17)protons/cm~2.Its propagating modes at 632.8 nm and 1539 nm were measured by the well-known prism coupling technique. The refractive index profile at either 632.8-nm wavelength or 1539-nm wavelength was optical barrier type in the proton-implanted Nd:CLNGG crystal optical waveguide, which was calculated by using the reflectivity calculation method. The near-field light intensity distributions were also simulated by the finite-difference beam propagation method in the visible and nearinfrared bands.     

Dispersive white-light spectral interferometry including the effect of thin-film for distance measurement

A spectral-domain white-light interferometric technique is used for measuring distances in a Michelson interferometer with a mirror represented by a thin-film structure (TFS) on a substrate. A fibre-optic spectrometer is employed for recording spectral interferograms that include wide wavelength range effects of dispersion in a cube beam splitter and multiple reflection within the TFS. Knowing the effective thickness of the beam splitter, its dispersion and parameters of the TFS and substrate, the positions of the second interferometer mirror are determined precisely by a least-squares fitting of the theoretical spectral interferograms to the recorded ones. We apply the technique to the beam splitter made of BK7 optical glass and to a uniform SiO₂ thin film on a silicon wafer. We compare the results of the processing that include and do not include the effect of the TFS.     

Diode-pumped efficient slab laser with two Nd:YLF crystals and second-harmonic generation by slab LBO

We demonstrate a diode-pumped electro-optical Q-switched slab laser with a high optical efficiency, high pulse energy, and short pulse width with two Nd:YLF crystals inside one resonator. The single compact slab resonator can generate a 1D top-hat beam at both the far field and the near field. With a slab-geometry-design lithium triborate (LBO) crystal, efficient critical phase-matching second-harmonic generation for a 1D top-hat beam with multiple transverse modes is achieved.     

Wavelength and temperature characteristics of BiYbIG film/YIG crystal composite structure for magneto-optical applications

We report the wavelength and temperature characteristics of novel Bi-substituted rare-earth iron garnet films grown on a YIG substrate by a modified liquid phase epitaxy (LPE) technique. The Faraday-rotation spectrum was measured by the magneto-optically modulated dual-frequency technique with the wavelength varied from 800 nm to 1700 nm. The resultant Bi_0.37Yb_2.63Fe₅O₁₂ (BiYbIG) LPE film/YIG crystal structure showed an increased Faraday-rotation coefficient due to Bi³⁺-ion doping on the dodecahedral sites of the iron garnet without increasing absorption loss; therefore, a good magneto-optical figure of merit, defined by the ratio of Faraday rotation and optical absorption loss, has been achieved (21.5 deg/dB and 30.2 deg/dB at 1300-nm and 1550-nm wavelengths, respectively, at room temperature). In addition, since the Yb³⁺ and Y³⁺ ions provide opposite contributions to the wavelength and temperature characteristics of the Faraday rotation, the resultant BiYbIG LPE film/YIG crystal structure showed a flat Faraday-rotation curve versus wavelength and temperature. The Faraday-rotation wavelength coefficient was reduced to 0.06 %/nm at 1550-nm wavelength. The Faraday-rotation temperature derivative was reduced to 0.006 deg/°C at 1300-nm wavelength and 0.007 deg/°C at 1550-nm wavelength, respectively. PACS 78.20.Ls; 81.15.Lm; 75.50.Gg     

Ultrabroad gain in an optical parametric generator with periodically poled KTiOPO4

An optical parametric gain bandwidth of 115 THz at full-width half maximum is generated from a picosecond Ti:sapphire pumped degenerate optical parametric generator. This ultrabroad bandwidth could be obtained by first identifying the wavelength where the nonlinear optical material has zero group-velocity dispersion (GVD). By pumping at half this wavelength the degenerate signal–idler pairs can accommodate ultrabroad bandwidths. The explanation for this is that the group velocities of the signal and the idlers are approximately matched and the GVD is small. However, in order to thoroughly investigate the degeneracy region around 1700 nm we fabricated several periodically poled KTiOPO₄ (PPKTP) crystals with different periods, and also one periodically poled RbTiOPO₄ (PPRTP). Both collinear and noncollinear configurations were employed for broadband parametric generation in this region. It was found that the optimum pump wavelength is in the region between 800 nm to 850 nm for PPKTP, and we could also conclude that a similar performance was found for PPRTP. This work will allow the design of optical parametric devices for generating few-cycle pulses in the spectral region between 1.1 μm and 3.8 μm. PACS 42.65.Re; 42.65.Ky; 42.65.-k     

Phase-matched self-doubling optical parametric oscillator

We report a synchronously pumped intracavity frequency-doubled optical parametric oscillator that employs a single KTiOPO(4) crystal for both parametric generation and frequency doubling. Both nonlinear processes are phase matched for the same direction of propagation in the crystal. The parametric oscillator, pumped by a femtosecond Ti:sapphire laser at a wavelength of 745 nm, generates a green output beam at 540 nm with a 29% power conversion efficiency. Angle tuning in conjunction with pump wavelength tuning provides output tunability in the 530-585-nm range.