The photorefractive properties of Mn-doped KNSBN crystals, especially the crystal with a higher doping level (0.09 wt.%), was studied. Experiment showed that the properties of Mn:KNSBN crystals with 0.09 wt.% are different from others. This maybe provides a good material to study the electron- hole competition, which exists widely in PR crystals. The high order harmonic properties were also investigated. Five orders of harmonics were observed. It was found that the maximum of the second order index grating shifts towards a small incident angle with respect to that of the fundamental grating. Based on the strong harmonics in this kind of crystals, the recording of harmonic index gratings was achieved by using a novel method in experiment.
We proposed a novel method to realize selective erasure of holographic index gratings in the photorefractive crystals. This scheme is based on the self-enhancement of the index gratings in the photorefractive materials. It is a save-erase- restore procedure, namely, save wanted information-erase unwanted information-restore wanted information. Simple experimental results are also presented. The requirement in this scheme is that the material has the effect of self- enhancement, i.e. the index grating is transmission grating, the product of the coupling constant and the thickness is above the threshold of the self-enhancement. But it eliminates the critical requirement of preventing vibration in the previous (pi) -phase-shift scheme.
Photorefractive crystals have many applications in holographic storage, optical communications, and nonlinear optical information processing. One problem is that the photorefractive holographic index gratings can be erased in the readout process. Several non-destructive approaches have been proposed and demonstrated in different photorefractive materials. Based on the initial research of domain fixing on KNSBN crystals, we studied the high order harmonic gratings during electrical domain fixing process in KNSBN crystals. In this paper, we mainly focus on the properties of the first order and second order harmonic index gratings of Mn-doped KNSBN crystal during electrical domain fixing process at room temperature. Domain fixing in Rh:SBN was also investigated, and the results in Mn:KNSBN and Rh:SBN were compared. In Mn:KNSBN crystals, the second order harmonic grating becomes stronger after fixing. This may be the main reason of the high noise in the revealed grating, which affects the image quality and fidelity. In addition, the effect of the accumulated charges in the revealing process was also discussed.
In this paper, we reported the electrical fixing results of photorefractive index gratings in Cu- and Mn-doped KNSBN crystals at room temperature. Due to the higher Curie temperature of KNSBN, the fixed grating may have a longer lifetime than SBN crystals, and the fixing results are different from the observation in SBN crystals. The relation between the applied field and the revealed grating is studied by analyzing the domain fixing process. We also reported the comparison of the fixing results in the single domain crystals and the multi-domain crystals. In the multi-domain crystals, the diffraction efficiency of the revealed grating is as about three times as that of the recorded grating. The probable reason is also discussed.
In this paper, a new kind of photorefractive Cu:KNSBN crystal with Li-replacement at A-sites ((Cu,Li):KNSBN) was reported. We studied the photorefractive properties of this kind of crystal by using the conventional two-wave mixing method. It revealed that the Li-replacement can improve the photorefractive response rate of the crystal which is very important in real time information processing. An response time of 90 ms was obtained at a total incident intensity of 3.92 W/cm2. The absorption spectrum and other photorefractive properties were also measured and discussed. Experiment showed that cation replacement such as Li- replacing at A-sites provides a new way to improve the photorefractive properties of KNSBN crystals.
We propose and demonstrate an all-optical pulse generator which is based on regenerative pulsation in optical bistable systems. The novel device consists of a nonlinear interference filter, a photorefractive crystal and an optical feedback loop. In such a pulse generator, when the input beam intensity exceeds the switch-on threshold of the system, a train of square-wave pulses will be produced. The firing rate is an increasing function of the intensity of the input beam. The principle of operation and the experimental results are presented and discussed.
An obvious minimum was observed in the reflectance spectrum of ion implanted Hg1-xCdxTe. The anodic oxidation method and beveling technique were used to learn the spectrum changing with the depth. This minimum even can be observed when a layer with thickness thicker than the ion range was removed from the implanted surface. Considering the high electron concentration of the implanted layer, this phenomenon was explained by using the model of reflection of layered media in which the refractive index changes with the depth. By numerical fitting, the depth profile of the carrier density and refractive the index of the ion implanted layer were obtained.
A two-dimensional thermal conducting model which deals with the thermal diffusion in continuous wave (cw) laser processing of material is presented in this paper. The temperature distribution during the interaction between HgCdTe and cw carbon dioxide laser is calculated using numerical method. Experiment is carried out to measure the damage threshold of HgCdTe with cw CO2 laser. The apparent damage temperature threshold, 670 - 680 K is obtained which corresponds to the solid-solid phase transition of HgCdTe. All the calculations are in good agreement with the experimental results.
In this paper, photorefractive (PR) crystals of Cu and Mn- doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 were symmetrically studied. We reported the growth conditions, the absorption properties and the photorefractive properties including two wave mixing (TWM) and self-pumped phase conjugation (SPPC). The mechanism of Cu-doped KNSBN was referred briefly, and the influence of the different sites occupied by doping ions on PR properties was also discussed. All these results reveal that: (1) In Cu-doped KNSBN crystals, the photorefractive properties become better with the increase of the doping level, such as higher effective charge carrier density, larger coupling coefficient, faster response rate, higher SPPC reflectivity. (2) The thinner sample shows larger coupling gain coefficient, which is due to the light creep effect and beam fanning effect. The response time becomes shorter with the decrease of the thickness. (3) In Cu:KNSBN crystals, the coupling gain coefficient of TWM was obtained up to 35 cm-1. (4) In Cu:KNSBN and Mn:KNSBN samples, the SPPC reflectivity up to 73% have been obtained, respectively. (5) The C-site in the tungsten-bronze structure of KNSBN has an effect on the PR properties of the crystal. All these results show that doping in KNSBN is an effective method to improve the PR properties. The Cu-doped KNSBN crystal is a very promising photorefractive material.
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