Laser beam defocusing at 1.06 μm by carrier excitation in silicon

Laser beams from a 15 ns pulsed Nd: YAG laser are defocused after passing silicon crystals with 400 m thickness. The beam profile changes into a ring structure at incident laser energies up to 30 mJ and energy densities of 440 mJ/cm². The experimental deflection angles agree with calculations assuming refractive index changes due to electronhole pairs produced by interband absorption.     

Picosecond four-wave mixing reflectivity of GaAs at 1.06 μm

The picosecond degenerate four-wave mixing reflectivity of semi-insulating gallium arsenide at 1.06 m is calculated in this paper. The dependence of the reflectivity on the pump and signal fluences is measured. Reflectivities of more than one are possible. The Fourier components of the excited-carrier densities are calculated as a function of the pump fluence. The wavefront-correction property of this reflectivity is demonstrated with a lens group in the signal beam.     

Thermal Lensing, Laser Performance at 1.06 μm and 0.53 μm of a NYAB Laser End-pumped by a Diode-laser-array

The thermal lensing, output characteristics of an end-pumped NYAB laser with high pump power levels and operated at the fundamental wavelength, and the manner of self-frequency-doubling, have been investigated. The thermal lensing in the NYAB crystal was found to be significantly stronger than that in Nd:YVO4 crystal. A maximum output of 3.2 W at 1.06 μm was achieved with an optical conversion efficiency of 29.1％ and an average slope efficiency of 37.5％. These results were found to be slightly inferior to those of Nd:YVO4 crystal. When operated in the fashion of selffrequency-doubling, 23 mW green output was obtained at the incident pump power of 5 W, such inefficient operation was attributed to the large mode size in the NYAB crystal.     

Laser induced electron emission from gold surface irradiated by picosecond pulses at λ=2.9 μm

A nonlinear photoelectric emission from a gold surface irradiated by intense (16 GW/cm²) ultrashort (100 ps) erbium laser pulses of the 3-micron wavelength region was observed. The results obtained were interpreted by the theoretically predicted thermally enhanced multiphoton photoemission.     

Heterodyne detection at 337 μm in epitaxial GaAs

The observation and quantative measurement of optical heterodyne detection at 337 μm using a HCN laser and an epitaxial n-type GaAs photoconductor are reported. The measured NEP amounted 1.4 × 10⁻¹⁴ W Hz⁻¹.     

Thermal Lensing, Laser Performance at 1.06 μm and 0.53 μm of a NYAB Laser End pumped by a Diode laser array

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Pulsed laser performance at 1.06 μm from Nd:SGGM

A single Xe gas filled flash lamp has been used to pump a Nd-doped SGGM rod 5 mm in diameter and 80 mm in length. Laser emission has been observed at 1.06 m in the free running mode of operation in the input energy range of 1–25 J. The laser performance has been evaluated using two different diffuse/filter combinations to block the ultraviolet radiation from the Xe lamp and the results have been compared. The intrinsic slope efficiency was determined to be approximately 1.5% with an 80% output coupler and a spectralon diffuser.     

Graphene mode-locked femtosecond laser at 2 μm wavelength

We experimentally demonstrated a passively mode-locked femtosecond laser by using a graphene-based saturable absorber mirror (graphene SAM) in the spectral region of 2 μm. The graphene SAM was fabricated by transferring chemical-vapor-deposited, high-quality, and large-area graphene on a highly reflective plane mirror. Stable mode-locked laser pulses as short as 729 fs were obtained with a repetition rate of 98.7 MHz and an average output power of 60.2 mW at 2018 nm.     

Simultaneous dual-wavelength operation at 1.06 and 1.34 μm in Nd-vanadate laser crystals

Output performances of Nd-vanadate lasers with simultaneous dual-wavelength emission on the 1.06-μm ⁴ F _3/2 → ⁴ I _11/2 transition and the ⁴ F _3/2 → ⁴ I _13/2 transition at 1.34 μm are discussed. The design uses a linear resonator for emission at 1.06 μm and an L-type folded resonator for the 1.34-μm wavelength, and the ratio between the power of a single wavelength and the total power is adjusted by the choice of the output mirror transmissions. A continuous-wave (CW) Nd:GdVO₄ laser with total output power in the range of 3.9 to 6.8 W and the corresponding ratio of the output power at 1.06 μm to the total output power between 0.26 and 0.97 is realized. It is also shown that in comparison with the pump at 808 nm, the pump directly into the ⁴ F _3/2 emitting level at 879 nm improves the total output power. Furthermore, a Nd:GdVO₄ laser with simultaneous emission at 1.06 and 1.34 μm and that generates also green light at 0.53 μm by intracavity frequency-doubling with LiB₃O₅ (LBO) nonlinear crystal is demonstrated.     

All-optical modulation at 1.3 μm wavelength in the inGaAsP/InP system

All-optical, normal-to-surface modulation in InGaAsP epitaxial layers, lattice matched to InP, is investigated. Close to the gap wavelength of 1.3 m a transmission increase under optical excitation is observed. A modulation depth of 34% is achieved for 0.8 mW pump power at 790 nm wavelength. The modulation frequency is limited by excess carrier lifetime. A 3 dB frequency of 80 MHz is achieved with a 10 dB decrease at 400 MHz. A lateral electric field enlarges the bandwidth but decreases the modulation depth. For weak excitation the experiments are well described in terms of direct electronic transitions between parabolic bands or in terms of simple band filling. The devices are well suited for parallel optical data processing.     

RCE photodiodes at wavelength band of 1.06

Resonant cavity enhancement (RCE) typed optical detector and modulator which operating at wavelength band of 1.06 μm is reported. The peak quantum efficiency of detector is reasonably high as 50% without bias, and the photocurrent contrast ratio of modulator is 3.6 times at -3.5 V as compared to 0 V. The incident angle dependence of RCE device's photoelectric response is investigated carefully.     

Laser absorption spectrometer using frequency chirped intensity modulation at 1.57 μm wavelength for CO2 measurement

We have demonstrated the laser-absorption spectrometer system using frequency chirped intensity modulation at 1.57 μm wavelength for measurement of CO(2) concentration. Using this technique, backscattered laser radiation from different ranges can be discriminated in the frequency domain of the electrical signal. We have reported the discrimination of two signals from the targets with different ranges. It is shown that stable measurements with short time fluctuation corresponding to 4 ppm (rms) were obtained with 32 s measurement intervals. Furthermore, there is qualitative good agreement on, at least, the diurnal changes between the results of the laser absorption spectrometer system and the in-situCO(2) sensor.     

Dependence of Er:Yb-codoped 1.5 μm amplifier on wavelength-tuned auxiliary seed signal at 1 μm wavelength

We report on experiments performed with a cladding-pumped single-mode Er:Yb-codoped single-frequency fiber amplifier simultaneously seeded by a distributed-feedback diode at 1556 nm and a tunable external-cavity diode laser emitting at a wavelength of about 1 μm wavelength. The influence of the output wavelength of the external-cavity laser on amplification and reabsorption behavior of the Yb emission as well as the amplifier performance at a wavelength of 1556 nm is examined experimentally.     

Diode-pumped passively Q-switched Nd:GdVO4 lasers operating at 1.06 μm wavelength

With a 10-W diode laser to pump Nd:GdVO₄ crystal in a folded cavity, we demonstrated Cr⁴⁺:YAG passively Q-switched Nd:GdVO₄ lasers at 1.06 μm. The maximum average output power of 2.1 W and the highest peak power of 625 W were, respectively, obtained when the initial transmissions of the Cr⁴⁺:YAG crystals were 90% and 80%. Received: 8 September 1999 / Revised version: 30 December 1999 / Published online: 8 March 2000     

Single-wall carbon nanotube assisted all-optical wavelength conversion at 2.05 μm

We fully demonstrate the special requirements of a mid-infrared all-optical wavelength converter. The construction mechanism of a 2.05 μm all-optical wavelength converter based on the single-wall carbon nanotube [SWCNT) is proposed.Systematic experiments are carried out, and the converter device is successfully developed. With the assistance of SWCNT-coated microfiber, the conversion efficiency up to-45.57 d B is realized, and the tuning range can reach9.72 nm. The experimental results verify th...     

Efficient Tm：YAG Ceramic Laser at 2 μm

We demonstrate a high-efficiency continuous-wave Tm： YAG ceramic laser pumped with a Ti：sapphire laser. An output power up to 860mW is obtained under an absorbed pump power of 2.21 W at 785nm, corresponding to a slope efficiency of 42.1% and optical to optical efficiency of 22%. The measured central wavelength is 2012nm.     

Four-wave mixing reflectivity of silicon at 1.06 μm: Influence of free-carrier absorption

The phase-conjugate reflectivity obtainable by degenerate four-wave mixing in silicon at a 1.06 m is calculated including free-carrier absorption. A maximum reflectivity of more than 100% is possible. The dependence of the reflectivity on the signal and pump energy densities up to 70 mJ/cm² is measured and found to agree with theory. The wave-front-correction property of DFWM is demonstrated with a lens in the signal beam.