AgGaS2 Crystal Research Articles

Nonlinear optical laser devices using GaSe

Tunable second-harmonic generation of CO2 laser radiation and tunable upconversion of infrared radiation from CO2-laser radiation in a GaSe crystal are demonstrated. The capability of low infrared-signal detection in this crystal is also explored and compared with the AgGaS2 crystal.

Mid-infrared pulse generation using a sub-picosecond OPO

We describe a synchronously pumped LBO parametric oscillator pumped by a cw mode-locked Ti:Sapphire laser. We demonstrate the synchronization between the pump pulses and the signal pulses by measuring a 100 fs cross correlation. We then generate pulses tunable from 2.6 to 5.3 µm by mixing the signal and idler pulses in an AgGaS2 crystal and obtain as much as 400 µW of average power.

Frequency upconversion by phase-matched sum-frequency generation in an optical parametric oscillator

We report the generation of 0.589-,microm radiation from mixing the pump at 1.064 ,microm and the signal at 1.319 microm of a singly resonant, synchronously pumped AgGaS(2) optical parametric oscillator. A KTP crystal is used for the sum-frequency generation (SFG). Both extracavity and intracavity SFG is demonstrated, with overall conversion efficiencies of 3.5% and 10.5%, respectively. Near-transform-limited pulses of less than 50 ps are generated from 100-ps pulses. With a limited available peak pump power, both spatial orderings of the KTP and the AgGaS(2) crystals for intracavity SFG produce similar conversion efficiency and outputs of similar pulse duration, spectral width, and stability.

Generation of 200 femtosecond pulses tunable between 2.5 and 5.5 �m

The signal and idler output of an optical parametric oscillator are mixed in LiIO3 and AgGaS2 crystals to generate infrared pulses with a repetition rate of 82 MHz and an average power of 500µW. The infrared pulses are tunable between 2.5 and 5.5 µm, have a duration of 200 fs and a peak-to-peak intensity fluctuation of less than 5 %.

Performance of AgGaS2 Crystal Filter for Raman Spectroscopy

The performance of a AgGaS2 crystal filter combined with a single monochromator is described for the use of Raman spectroscopy. The filter can be utilized in both band-pass mode and band-elimination mode near 497 nm with a narrow band width of 1.5 nm. A dye laser tuned at 497.3 nm can be used as an excitor since the center wavelength of the filter is located exactly at the wavelength. On the other hand, the precise center wavelength of the filter can be easily adjusted to the 496.5 nm line of an Ar+ laser excitor by temperature tuning at -23.5° C. High rejection of laser lines of both excitors is proved in the Raman spectroscopy performance test.

Tangentially phase-matched infrared detection in AgGaS2

Detection of infrared radiation (10 mu m) by a nonlinear up-conversion technique under a tangential phase-matched situation in AgGaS2 crystal with Nd:YAG laser as a pump has been demonstrated. A wide angular tolerance has also been obtained with a view to achieving mechanical stability. Its capability of detecting a low-level infrared signal at room temperature and its temperature-dependency have also been demonstrated.

Measurements of second-order nonlinear optical coefficients from the spectral brightness of parametric fluorescence

We report a new technique for determining second-order nonlinear optical coefficients that uses the spectral brightness of spontaneous parametric fluorescence. Measurements with this technique on two separate AgGaS2 crystals yielded values of 22.9 and 24.3 pm/V for |d36|, and measurements on a KTP crystal yielded 4.1 pm/V for |d24|. The uncertainty of the determined values is approximately ±10%.

Ionic Displacements and Piezoelectric Constants of AgGaS2 from X-Ray Diffraction of a Crystal in an External Electric Field

The displacements of the ions and the changes in cell parameters which occur on application of an electric field to a crystal of AgGaS2 have been determined using X-ray diffraction. The shifts in Bragg angle of 14 reflections, due to a field of 2.6 × 106 V/m applied nearly parallel to [221], were used to refine the change in cell parameters. The resulting piezoelectric coefficients are d14 = d25 = 8.8 (0.9) × 10-12 C/N and d36 = 7.6 (1.8) × 10-12 C/N. This leads to a value of 4.8 (0.5) × 10-12 pC/N for the piezoelectric constant in the [221] direction, which compares well with a value of 5-6 × 10-12 C/N measured directly. The ionic displacements were studied for two field directions. With E = 2.6 × 106 V/m in a direction parallel to [110], very small, but significant a and b direction displacements were observed for all atoms, whereas the displacements in the e direction were negligible as expected. Relative to the sulfur framework, the Ga ion displacement is considerably larger than that of the Ag ions. The changes in scattering intensity for a field parallel to [221] were found to be much smaller, indicating smaller ionic displacements for that field direction. The ion displacements are analyzed with a model of nonpolarizable harmonic oscillators in an electric field. It is found that the observed displacements of the Ga ions are much larger than the calculated displacements, whereas the displacements of the Ag ion are in good agreement with theory.

Two-color synchronously mode-locked femtosecond Ti:sapphire laser

We report the simultaneous generation of two collinear synchronous mode-locked pulse trains, with central wavelength separations of 60 to 80 nm, from a single-cavity mode-locked Ti:sapphire laser. Near-transform-limited pulses of duration 50 to 70 fs were generated at each wavelength, with jitter of less than 20 fs between the two-color pulses. These pulses were directly used to generate infrared pulses centered at 9 μm, by difference-frequency mixing in an AgGaS2 crystal.

Crystal growth of AgGaS2 by the Bridgman-Stockbarger and travelling heater methods

Single crystals of AgGaS2 were grown by the Bridgman-Stockbarger technique in two-zone furnaces and by the travelling heater method in ellipsoid mirror furnaces. PbCl2 and AgBr were proved to be novel solvents for the high temperature solution growth of AgGaS2. Melt grown AgGaS2 crystals show weak transparency. Optically clear AgGaS2 crystals could be obtained after annealing them in the presence of Ag2S. Flux grown AgGaS2 crystals are transparent without annealing, but show microscopically small inclusions originated from the solvents.

High-power source of coherent picosecond light pulses tunable from 0.41 to 12.9 ?m

We report a high-power source of coherent picosecond light pulses based on optical parametric generation and amplification in LiB3O5 and AgGaS2 crystals. The spectral range of this continuously tunable source covers the visible, near-infrared and medium-infrared spectrum from 0.41 to 12.9 μm. An optical parametric generator and amplifier, consisting of two type-I phase-matched LiB3O5 crystals and a diffraction grating, is pumped by the third harmonic of a picosecond Nd:YAG laser and provides spectrally narrow, high-power pulses from 0.41 to 2.4 μm. Energy conversion efficiencies up to 16 percent are achieved. The pulse duration is about 14 ps, the bandwidth between 10 and 30 cm−1. The tuning range is extended to 12.9 μm by mixing the infrared output between 1.16 and 2.13 μm with the fundamental of the Nd:YAG laser in type-I-phase-matched AgGaS2 crystals. Up to 25 percent of the pulse energy at 1.064 μm is converted into parametric infrared pulses. Bandwidths between 3 and 8 cm−1 and a pulse duration of approximately 19 ps are measured for these pulses. We also observe a retracing behaviour in the tuning curve of AgGaS2 not reported before.

Single-Crystal X-Ray Diffraction Study on Structural Change of AgGaS2 with Increasing Pressure

Single-crystal X-ray diffraction study under high pressures has been carried out on silver thiogallate, AgGaS2, to investigate the phase transition at about 42 kbar. The crystal of AgGaS2 is tetragonal with the space group I4̄2d having the cell dimensions a=5.7603(6) and c=10.299(2) Å under the ambient pressure. The high-pressure form has a similar unit cell to that of the ambient pressure form. The diffraction pattern around the [221̄] zone axis at 47 kbar indicated that the high pressure form has weak but clear hhl reflections which do not satisfy the systematic absence condition, 2h+l=4n, for the space group I4̄2d. It has been concluded that the diamond glide planes parallel to {110} present in the ambient pressure form disappear in the high pressure form.

Optimization of a midinfrared high-resolution difference-frequency laser spectrometer

Improved performance of a continuous-wave (cw) laser spectrometer for Doppler-limited infrared spectroscopy of molecules based on difference-frequency generation (DFG) in AgGaS2 has been achieved. The spectrometer was configured to generate continuous scans of up to 1 cm−1 from 1550 to 2100 cm−1. An absolute precision of ∼6 × 10−3 cm−1 with a resolution of better than 1.0 MHz (3.3 × 10−5 cm−1) was achieved. Infrared powers of ∼20 μW were obtained by employing 90° Type I phase matching in a 45-mm-long AgGaS2 crystal. The high-resolution characteristics of the DFG spectrometer were evaluated by using H2O and N2O spectra. Preliminary infrared kinetic spctroscopy results involving the detection of transient CO radicals from 193-nm acetone photodissociation are also reported.

Accurate determination of strain tensors from small shifts of reflections measured on a four-circle diffractometer

Formulas are given for the derivation of the changes in Bragg angles and the corresponding full asymmetric strain tensor from the shifts of reflections measured on a four-circle diffractometer. The effects of using either an ω- or a 2θ-scan mode are discussed. A least-squares program was written on the basis of the derived formulas and applied to data measured on the piezoelectric crystals of AgGaS2 under the influence of an external electric field. The obtained piezoelectric constants are in good agreement with values determined by conventional methods.

Ionic Displacements and Piezoelectric Constants of AgGaS2 from X-Ray Diffraction of a Crystal in an External Electric Field.

AbstractWe have determined the displacements of the ions and the changes in cell parameters which occur on application of an electric field to a crystal of AgGaS2, using a three-step modulation method. The shifts in Bragg angle of 14 reflections, due to a fieldof 2.6 x 106 V/m applied nearly parallel to [221], were used to refine the change in cell parameters. The resulting piezo-electric coefficients are d14=d25 =8.8 (0.9) 10-12 C/N and d36=7.6 (1.8) 10-12 C/N. This leads to a value of 4.8 (0.5) pC/Nfor the piezoelectric constant in the [221] direction which compares well with a value of 5-6 10-12 C/N determined by other methods. The ionic displacements were studied on a second sample, with E=2.6x 106 V/m in adirection parallel to [110]. Very small, but significant a and b directiondisplacements were observed for all atoms, whereas the displacements in the c direction were negligible as expected. Relative to the sulfur framework, the Ga ion displacement is considerably larger than that of the Ag ions.

Recent Developments In The Growth Of Chalcopyrite Crystals For Nonlinear Infrared Applications

Improvements in crystal growth technology have made it possible to grow crack- and twin-free boules of AgGaS2 and AgGaSe2 in comparatively large dimensions, AgGaS2 to 28 mm diameter by 100 mm length and AgGaSe2 to 37 mm diameter by 100 mm length. Although the crystals grow with optical defects (micrometer-size scattering centers), postgrowth heat treatment procedures have been used to successfully eliminate the defects and produce material of near-theoretical transparency. High optical quality, oriented single crystals of AgGaS2 1 cm in cross section and more than 2 cm in length and of AgGaSe, 1 cm in cross section and more than 3.5 cm in length have been produced and are leading to new advances in IR frequency generation. The optical and phase equilibrium studies as well as details of the crystal growth technology that led to this advance in materials technology are described.

Effect of annealing on the optical quality of AgGaS2 and AgGaSe2 single crystals

Single crystals of AgGaS2 and AgGaSe2 were grown by a modified Bridgman-Stockbarger technique. Pieces of sizes 10 mm × 6 mm × 4 mm and 11 mm × 6 mm × 5 mm of AgGaS2 and AgGaSe2 free from lamellar twins, were cut from the crystals for detailed investigations. The results of infrared transmittance and absorbance measurements indicate that the optical quality of the annealed crystals was much better than that of the as-grown crystals. Experiments on thermal etching were also carried out to study the microscopic defects in the crystals.

Low resistivity silver thiogallate (AgGaS2) layer growth by liquid phase epitaxy

By comparison to pure, bulk single crystal or epitaxial layers of AgGaS2 of resistivity ⩾1012Ω cm, Ge doped AgGaS2 layers show a substantial lowering of resistivity. Growth of low resistivity (105106 Ω cm) Ge doped AgGaS2 by liquid phase epitaxy on AgGaS2 substrates is reported, for the first time, using KCl primarily as a solvent. A partial temperature composition (T-X) phase diagram for the Ge-AgGaS2 and a binary section of the Ge-AgGaS2-KCl systems are presented. Good crystalline quality and morphology of the epilayers were observed.

Parametric generation of tunable picosecond pulses in the medium infrared using AgGaS2 crystals

Infrared pulses were generated over the range from 1.2 to 10 μm in a single path system consisting of two AgGaS2 crystals. A high photon conversion efficiency between 10−1 and 10−3 was found depending upon the emission frequency. A bandwidth of approximately 10 cm−1 for idler pulses between 6 and 10 μm was observed. With a Nd:yttrium aluminum garnet laser pump of 20-ps pulse duration one observes parametric pulses of 8 ps.

Temperature effects in AgGaS_2 nonlinear devices

Refractive indices of AgGaS2 crystal are measured at different temperatures using the classical minimum deviation technique and are fitted in appropriate dispersion relations. The variation of pump laser wavelength for noncritical upconversion of signal at 10.6 microm with the change in crystal temperature has been verified using the above data. Temperature tunable infrared generation by noncritically phase-matched difference- frequency mixing has been predicted from 3 to 18 microm.