DKDP Crystals Research Articles

Electro-Optic Characteristics of a Cooled Deuterated Potassium Dihydrogen Phosphate Crystal

The half-wave voltage of a deuterated potassium dihydrogen phosphate (DKDP) crystal was measured between 231 K and room temperature. It was found to decrease linearly with crystal temperature at a rate of 55.1 V/K. The lowest voltage of 511 V was observed at 231 K, which is one eighth of that at room temperature. The cooled DKDP crystal was discussed for use as an electro-optic modulator as it provides various advantages such as the reduced voltage of the power supply needed and the lower B-integral.

不同波长三倍频DKDP晶体的激光损伤

不同波长三倍频DKDP晶体的激光损伤

One-pulse driven plasma Pockels cell with DKDP crystal for repetition-rate application

Pockels cell (PPC), which can use a thin crystal to perform the uniform electro-optical effect, is ideal component as average-power optical switch with large aperture. In this paper, the key problems in PPC are analyzed for repetition-rate application, and thermo-optical effects are simulated by means of numerical modeling when average power is loaded on the electro-optical crystal. By reformative design and employing a capacity to share the gas discharge voltage, the DKDP PPC driven by one pulse is realized. As gas breakdown delay time is stable, and discharge plasma is uniformly filled the full aperture, it meets the demand of plasma electrode for the repetition-rate PPC with DKDP crystal. The switch efficiency of PPC at the whole aperture is better than 99%.

Characteristics of 355 nm Laser Damage in KDP and DKDP Crystals

We present the characteristics of bulk damage induced by the third harmonic of Nd:YAG laser irradiation in KDP and DKDP crystals. Bulk damage occurs as a few or a series of pinpoints consisting of a core and the deforming zone. The results of a 1-on-1 test reveal that the pinpoint size increases with inevreasing fluence, and the pinpoint density increases exponentially with increasing fluence. The results of an s-on-1 test indicate that the pinpoint density increases gradually with laser pulse number, but the size does not grow. These results are consistent with a model in which nanoabsorbers are assumed to exist in the crystal and the initiation of damage is determined by heating them to the critical temperature.

A Thermal Approach to Model Laser Damage in KDP and DKDP Crystals

A thermal model is considered in order to better understand the mechanism of laser induced damage in KDP and DKDP crystals. We demonstrate that the expressions of pinpoint density and damage probability, predicted by the thermal model, are consistent with the experimental data. We also discuss the effect of particle interaction on the thermal model.

Generation of a regular sequence of short-pulse microtrains with a discretely varied repetition period

In the Nd:YAG lamp-pumped laser controlled by optoelectronic negative feedback based on an electro-optic DKDP crystal, the mode of generation of a millisecond sequence of short-pulse microtrains with a discretely varied repetition period was implemented. The microtrain repetition periods are fixed and controlled by resonances of shear acoustic oscillations of the crystal. The cavity design allowed selective excitation of the first ten acoustic modes in the period range of 8–0.5 µs.

Growth Characteristics and Mechanism of Surface and Bulk Damage in KDP and DKDP Crystals

By testing the number increase and size growth of surface and bulk laser induced damage in KDP and DKDP crystals, we observe different growth characteristics of surface and bulk damage under multiple 355 nm laser irradiations. The size of the surface damage grows exponentially, but that of the bulk damage does not grow. In contrast, the bulk damage number increases, but that of surface damage does not increase significantly. We attribute the differences to the different formation of the damage initiators and the different damage testing volumes.

One-on-One and R-on-One Tests on KDP and DKDP Crystals with Different Orientations

By testing a substantial number of tripler and z-cut KDP and DKDP crystals, we have observed that at 355 nm, the laser induced damage threshold in the R-on-one test is higher than that in the one-on-one test. It is proved that laser conditioning is an efficient way to improve the damage resistance. The efficiency of laser conditioning becomes increasingly good with smaller ramping ffuence steps. We have also found that the damage resistance of the z-cut crystal is higher than the tripler cut, and the pinpoint number is definitely less in the z-cut crystal. The reason for these observations is discussed.

Conical Double Frequency Emission by Femtosecond Laser Pulses from DKDP

Conical double frequency emission is investigated by femtosecond laser pulses at a wavelength of 800 nm in a DKDP crystal. It is demonstrated that the sum frequency of incident wave and its scattering wave accounts for the conical double frequency emission. The gaps on the conical rings are observed and they are very sensitive to the propagation direction, and thus could be used to detect the small angle deviation of surface direction.

Compact 300-J/300-GW Frequency-Doubled Neodymium Glass Laser—Part II: Description of Laser Setup

All the basic elements of a 300 J/1 ns Nd:glass laser with high-efficiency (70%) frequency conversion are described in detail. These include a seed laser, a system shaping the spatial structure of the beam, a six-cascade amplifier based on neodymium phosphate glass rods 10-100 mm in diameter, and a second-harmonic generator on a DKDP crystal with ooe interaction. Reliable and easy operation guaranteed long-term functioning of the laser as a pump for the output cascade of a chirped pulse parametric amplifier in a petawatt laser complex.

Output energy parameters of a KULON-10Cu-UV laser

The output energy parameters of an industrial KULON copper vapour laser equipped with a nonlinear frequency converter based on DKDP and BBO crystals are studied. The average and peak powers, as well as the energies and pulse durations of radiation at wavelengths of 510, 578, 255, 271, and 289 nm, are measured in the regime of high-speed pulse modulation, which is used in lasers of this series. The maximum average power was 420 mW at a wavelength of 271 nm (DKDP) and 350 and 110 mW at 255 and 289 nm, respectively (BBO). It is experimentally shown that the average energy characteristics of UV radiation can be controlled on-line by changing the pulse repetition rate of the laser.

Optical unit of Laser-Electron X-ray Generator designed for medical applications

A design of optical unit for pulsed Laser Electron X-Ray Generator is proposed. The generator provides the exposure 0.1–1 ms at frame rate 30 Hz. It consists of a completely passive circulator based on second harmonic generation and a picosecond laser system which includes a master oscillator, pulse picking systems and amplifiers. To specially arrange the output time structure, two master oscillators controlled with optoelectronic negative feedback are proposed and tested. The first system allows to obtain regular bursting with period from 25 to 75 cavity round trips smoothly varied by the voltage applied to the Pockels cell based on TaLiO 3 crystal. In the second laser system secondary electro-optic effect in a DKDP crystal of Pockels cell is used and the period of regular bursts is varied discretely from 7.8 μ s down to 0.52 μ s .

Central Peak in Raman Spectra of Ferroelectric KDP and DKDP Crystals

The ferroelectric phase transition in K(H1 − x D x )2PO4 crystals was investigated by Raman scattering. It was found that the temperature dependence of the central peak in typical order—disorder crystals K(H 1 − x D x )2PO4 consists of three temperature ranges: in the nearest vicinity of the phase transition temperature the width and the amplitude of the central peak follow the theoretical predictions; in the second temperature range the “critical slowing down” is manifested whereas the behavior of the amplitude is strongly nonlinear; and outside these temperature ranges the central peak does not follow the theoretical predictions.

Transmission measurements in rapid growth KDP and DKDP crystals

Rapid growth methods used to synthesize potassium dihydrogen phosphate crystals (KDP) and their partially deuterated form (DKDP) have been shown to increase the level of their impurities. These impurities may have a strong impact on the optical performance of such crystals. Transmission measurements have thus been performed on rapidly grown KDP crystals in order to evaluate the influence of impurities on the crystal transmission properties. The latter data have been compared with a DKDP transmission spectrum. A difference appears that can be explained by an analogy with the transmission spectra of water and deuterated water. This study also enables us to obtain information about the value of the optical band gap.

Laser annealing characteristics of multiple bulk defect populations within DKDP crystals

Laser annealing by pre-exposure to subdamage threshold laser pulses is a well-established method to increase the damage performance of bulk KH2PO4 and KDxH2−xPO4 nonlinear optical materials. The origin of laser-induced damage is believed to be localized absorption by a defect structure, either a light-absorbing foreign nanoparticle or a cluster of stoichiometric defects. It has been recently shown that there are at least three populations of such defect structures in these materials in which pre-exposure to laser pulses of specific fluence and wavelength results in a measurable reduction in their number density or decrease in their susceptibility to damage. In this work, we investigate the annealing characteristics of these three populations of defect structures in DKDP under variable irradiation conditions. The aim is to understand the similarities and differences between these populations in the way they interact with laser light. The results depict distinct behaviors that reveal information on the relationship between the defect populations and their modifications responsible for annealing.

The effect of material, thermal and laser conditioning on the damage threshold of type II tripler‐cut DKDP crystals

AbstractBy using the traditional temperature‐reduction method, KD2PO4 (DKDP) crystals were grown from 85%‐deuterated aqueous solution synthesized by different kind of KH2PO4 (KDP) raw materials. An experimental technique was employed to measure the variation of bulk damage threshold in plates of DKDP crystals. Bulk laser damage in unconditioned, thermal‐conditioned and laser‐conditioned type II tripler‐cut DKDP crystals has been studied using 1064 nm (ω) and 355 nm (3ω) laser at pulse lengths of 5ns, 5ns respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Low-frequency Raman scattering study of the ferroelectric phase transition in the DKDP crystal

The low-frequency Raman scattering spectra of the DKDP ferroelectric crystal are studied in the temperature range 30–393 K. At temperatures above 150 K, the Raman spectra exhibit a central peak which reflects the lattice relaxation susceptibility. The width and integrated intensity of the central peak are derived from the experimental spectra. The critical slowing down of the relaxation response predicted by the Ginzburg-Landau-Devonshire theory is observed throughout the temperature range in which the central peak persists. Its integrated intensity does not, however, follow the predictions of the theory and reveals a strong temperature dependence in the ferroelectric phase and a weaker dependence in the paraphase. It is shown that the thermal activation law describes well the temperature dependence of the intensity of the central peak. An interpretation is proposed according to which the intensity of order parameter fluctuations is related to the activation barrier whose height is proportional to the deviation from the phase transition temperature.

New design of the temperature controlled pockels cell for IFE driver

We have observed the temperature dependence of the electro-optic coefficients of the DKDP crystal from 298K to the 231K. The half-wave retardation voltage was decreased proportionally with the crystal temperature at the rate of 55.1 V/K. The lowest half-wave voltage was 551 V at the crystal temperature of 231K, which corresponded to 1/8 of that at the room temperature. Note that the low operation voltage of 511 V may permit the use of semiconductor electrical switches instead of the thyratron.

Concept study of a 100-PW femtosecond laser based on laser ceramics doped with chromium ions

A new concept of a superpowerful femtosecond laser based on CPA in polycrystalline chromium doped ceramics (Cr:YAG, Cr:YSGG, etc.) pumped by a Nd:glass laser is proposed. In contrast to amplifiers in available petawatt laser systems (neodymium glass, titanium-doped sapphire, and parametric amplifiers with a DKDP crystal), these ceramics combine three key favorable properties: a large gain bandwidth to amplify chirped pulses with less than 20-fs durations, a wide aperture to amplify chirped pulses to the multikilojoule level, and a high conversion efficiency of narrowband Nd:glass laser pulses into chirped pulses. These properties open up the opportunity to create a unique laser with a peak power of 100 PW at a 10-kJ pump power.

Quasiharmonic approximation for a double Morse-type local potential model: Application to aKH2PO4-type phase diagram

In order to describe a structural phase transition at low temperature, a quantum particle within a local potential is considered. According to the general formalism presented by Salje et al. [Z. Phys. B 82, 399 (1991)], a quasiharmonic approximation is applied to the local potential and the interaction is replaced by the mean field one. The rigorous effective potential is reduced from a double Morse-type potential. The order parameter, the variance, and the effective soft frequency are given by analytic equations with potential parameters. As an application, a molecular motion of ${\mathrm{H}}_{2}\mathrm{P}{\mathrm{O}}_{4}$ in KDP is considered and the disappearance of the ordered phase at low temperature under high pressure is discussed. The difference between KDP and DKDP crystals are described successfully by the presented model.