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.     

Laser induced damage in GaAs at 1.06 μm wavelength: surface effects

An experimental study of single shot damage to monocrystal GaAs by a free running laser pulse of 1.06 μm wavelength is described. In order to see the role of surface effects on laser induced damage, samples of different surface finish were prepared. The laser induced damage threshold (LIDT) of lapped GaAs samples is considerably lower than that of the mirror polished samples (ratio ). Damage threshold results are analysed in terms of a thermal model incorporating the temperature dependent thermal and optical parameters of GaAs. The combined effect of the enhanced surface absorption and high surface recombination velocity of photo-excited carriers significantly enhances the surface temperature rise and reduces the damage threshold value of GaAs. The evolution of damage morphology is governed by the mechanical damage caused due to the polishing process.     

Picosecond photorefractive diffraction in CdTe at 1 μm

Using a ps-transient grating technique the contribution of the ps-photorefractive effect to the first-order probe-beam diffraction signal has been studied in CdTe at 1 m investigating diffraction kinetics at different sample orientations in the thin grating regime. A fast photorefractive grating formation time during the pump pulses and a characteristic decay time of 600 ps, shorter than the free-carrier lifetime, have been observed.     

Picosecond passively mode-locked GaSb-based semiconductor disk laser operating at 2 μm

We report on a passively mode-locked optically pumped GaSb-based semiconductor disk laser producing stable picosecond optical pulses at a 1.95 μm wavelength. The gain mirror was comprised of a 15 quantum well InGaSb/GaSb structure. A fast semiconductor saturable absorber mirror with three InGaSb/GaSb quantum wells was used to attain self-starting mode-locked operation at a fundamental repetition rate of 881.2 MHz. The laser produced pulses with 30 pJ energy and a duration of 1.1 ps within a factor of 2 of the Fourier limit.     

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.     

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.     

Absorption spectrum of HDO in the 1.06 μm region at a temperature of 1000 K

In the 9387–9450 cm^–1 region at temperatures of 300–1000 K, we have used an intracavity laser spectrometer based on a neodymium laser with threshold sensitivity to absorption 10^–8 cm^–1 and spectral resolution 0.035 cm^–1 to study the absorption spectrum of D₂¹⁶O, H₂¹⁶O, and HD¹⁶O vapor. The high-temperature spectrum contains more than 450 absorption lines, 240 of which are assigned to the HDO isotopomer. The absorption lines of HDO were identified and belong to nine vibrational transitions: 3ν₂ +ν₃, 2ν₁ + 3ν₂, 2ν₁ + ν₃, 4ν₂ + ν₃, 7ν₂, ν₁ + 2ν₂ + ν₃, ν₁ + 5ν₂, ν₁ + 2ν₂, and 3ν₃ – ν₂.     

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.     

Multicolor femtosecond laser with μJ level by cascaded four-wave mixing

We obtained an array of multicolored femtosecond laser pulses with as many as 17 different colors that are spatially isolated. The mechanism of generation was proved to be cascaded four-wave mixing and with the following procedure. The output beam from a femtosecond laser was split into two. One of the two beams was pulse-compressed with a hollow core fiber and the intensity of the other was reduced. The two beams were synchronized and combined with a small crossing angle in a plate of fused silica glass plate. The wavelengths of the sidebands are continuously tunable from near-ultraviolet to near-infrared. The pulse duration, spatial mode, spectrum, and energy stability of the sidebands were studied. As many as fifteen spectral up-shifted pulses and two spectral downshifted pulses were obtained with spectral bandwidths broader than 1.8 octaves. Properties such as pulse energy as high as 1 μmJ, 45 fs pulse duration, smaller than 1.1 times of the diffraction limit Gaussian spatial profile, and better than 2% RMS power stability of the generated sidebands make it can be used in various experiments. The characterization showed that the sidebands have sufficiently good qualities to enable application to for various multicolor femtosecond laser experiments, for example, a multicolor pump-probe experiment.     

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.     

Electroabsorption modulators operating at 1.3 μm on GaAs substrates

This paper describes the growth and device performance of electroabsorption modulators on GaAs substrates operating near 1.3 m, the dispersion minimum for silica fibres. The key to the successful molecular beam epitaxial (MBE) growth of these devices was the incorporation of a linearly-graded buffer layer beneath the InGaAs/AlGaAs multi-quantum-well active layer. Both transmission and reflection modulators are produced. For transmission devices, larger modulation is achieved when the buffer is graded more slowly: The maximum modulation reported was 22% for T/T _O corresponding to a 0.86 dB contrast ratio with an insertion loss of roughly 5 dB at 1.34 m. Antireflection coating a transmission modulator yields a reasonable reflection modulator. However, improved performance is reported for a reflection modulator using a novel technique of integrating the bottom quarter-wave mirror into a buffer with linearly-graded In composition. At 1.33 m, a normally-off reflection modulator with an integrated mirror exhibited a R/R _O of 73%, a constrast ratio of 2.38 dB, and an insertion loss of 4 dB.     

Absorption spectrum of C2 molecules near 1.06 μm

An intracavity laser spectrometer has been used to study the laser-spark absorption spectrum of C₂ radicals near 1.06 μm. The spectra recorded have been assigned, and the rotational lines of the transitions 3-0, 4-1, and 5-2 b ³Σ _g ^? -a ³Π _u and 2-1 and 1-0 A ¹Π _u -X ¹Σ _g ⁺ have been identified. The vibrational and rotational temperatures have been determined.     

Design and Fabrication of 1.06 μm Resonant-Cavity Enhanced Reflective Modulator with GaInAs/GaAs Quantum Wells

A resonant-cavity enhanced reflective optical modulator is designed and fabricated, with three groups of three highly strained InGaAs/GaAs quantum wells in the cavity, for low voltage and high contrast ratio operation. The quantum wells are positioned in antinodes of the optical standing wave. The modulator is grown in a single growth step in an molecular beam epitaxy system, using GaAs/AlAs distributed Bragg reflectors as both the top and bottom mirrors. Results show that the reflection device has a modulation extinction of 3 dB at -4.5 V bias.     

Efficient laser emissions at 1.06 μm of swift heavy ion irradiated Nd:YCOB waveguides

We report on the fabrication of Nd:YCOB (Nd:YCa(4)O(BO(3))(3)) optical waveguides by using 170 MeVAr(8+) ion irradiation at an ultralow fluence of 2×10(12) ions/cm(2). The confocal microphotoluminescence investigation on the produced waveguides has shown the well-preserved fluorescence features within the guiding layer with respect to the bulks. Under the optical pump at wavelength of 810 nm, continuous wave waveguide lasers at 1061.2 nm have been generated at room temperature with a high slope efficiency of ~67.9%.     

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.     

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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A comparative study of laser tissue interaction at 2.94 μm and 10.6 μm

Laser cutting of gelatin and tissue with Er and CO₂ lasers is explained by combined action of evaporation, ejection of liquid and elastic deformation of the region of radiation impact. It is shown that the ejection mechanism is more pronounced at 2.94 m than at 10.6 m. The use of high speed photography has revealed the influence of the temporal pulse shape. The experimental results are explained by a thermo-mechanical model.     

Efficient Cr3+ sensitized Nd3+: GdScGa-garnet laser at 1.06 μm

Room-temperature cw lasing at 1.061 m has been obtained in Cr,Nd: GdScGa-garnet. Threshold powers as low as 7 mW and slope efficiencies up to 41% have been measured. Cross pumping of Nd³⁺ via Cr³⁺ is nearly as efficient as direct pumping. Time-resolved measurements of the transfer rate yield a transfer efficiency of 0.86 and an average transfer time of 17 s. An improvement in pulsed broad band pumping can also be expected.