Chemical oxygen iodine laser, or COIL, is an impressive type of chemical laser and is widely adopted in the past several decades. A novel approach for obtaining high power vortex beam is explored. A seed vortex beam is amplified by a chemical oxygen iodine amplifier. Numerical simulation is carried out to confirm the feasibility of obtaining high power vortex beam based on chemical oxygen iodine amplifiers. The behavior of the vortex beam is also revealed. As the beam is modulated by the gain media, the beam profile gets asymmetric, and the vortex center no longer locates at the midpoint between the upstream and downstream intensity maximum points. This study suggests a potential approach for developing chemical oxygen iodine lasers.
Chemical oxygen iodine laser, or COIL, is an impressive type of chemical laser that emits high power beam with good atmospheric transmissivity. Chemical oxygen iodine lasers with continuous-wave plane wave output are well-developed and are widely adopted in directed energy systems in the past several decades. Approaches of generating novel output beam based on chemical oxygen iodine lasers are explored in the current study. Since sophisticated physical processes including supersonic flowing of gaseous active media, chemical reacting of various species, optical power amplification, as well as thermal deformation and vibration of mirrors take place in the operation of COIL, a multi-disciplinary model is developed for tracing the interacting mechanisms and evaluating the performance of the proposed laser architectures. Pulsed output mode with repetition rate as high as hundreds of kHz, pulsed output mode with low repetition rate and high pulse energy, as well as novel beam with vector or vortex feature can be obtained. The results suggest potential approaches for expanding the applicability of chemical oxygen iodine lasers.
A novel optimization method, stochastic parallel proportional-integral-derivative (SPPID) algorithm, is proposed for high-resolution phase-distortion correction in wave-front sensorless adaptive optics (WSAO). To enhance the global search and self-adaptation of stochastic parallel gradient descent (SPGD) algorithm, residual error and its temporal integration of performance metric are added in to incremental control signal’s calculation. On the basis of the maximum fitting rate between real wave-front and corrector, a goal value of metric is set as the reference. The residual error of the metric relative to reference is transformed into proportional and integration terms to produce adaptive step size updating law of SPGD algorithm. The adaptation of step size leads blind optimization to desired goal and helps escape from local extrema. Different from conventional proportional-integral -derivative (PID) algorithm, SPPID algorithm designs incremental control signal as PI-by-D for adaptive adjustment of control law in SPGD algorithm. Experiments of high-resolution phase-distortion correction in “frozen” turbulences based on influence function coefficients optimization were carried out respectively using 128-by-128 typed spatial light modulators, photo detector and control computer. Results revealed the presented algorithm offered better performance in both cases. The step size update based on residual error and its temporal integration was justified to resolve severe local lock-in problem of SPGD algorithm used in high -resolution adaptive optics.
KEYWORDS: Resonators, Mirrors, Chemical oxygen iodine lasers, Near field, Near field optics, Computer simulations, Chemical lasers, Optical simulations, Algorithms, Optical resonators
Unstable resonator with nonuniform magnification for improving the beam uniformity of chemical oxygen iodine lasers is explored for the first time. The magnification of the resonator is a function of the radial coordinate of the polar coordinate system on the front mirror surface. A resonator was designed to have a lower magnification at the center of the resonator than at the edge. The resonator consists of two aspherical mirrors. Method for designing the resonator is given. The energy conservation law and the aplanatic condition were used to derive the designing principle of the two aspherical mirrors. The design result was fitted to polynomial form which is suitable for manufacturing. Numerical experiment was carried out to evaluate the performance of the resonator. The computation was based on coupled simulation of wave optics model and computational fluid mechanics model. Results proved the effectiveness of the design method. The design tends to enhance the intensity near the center of the output beam and cripple that near the edge. Further analysis revealed that this effect is induced because rays of light are reflected more densely at the center of the pupil than at the edge. Therefore, this design affords for a potential approach for improving the near field uniformity of chemical oxygen iodine lasers.
An optical key distribution method based on aero-optical effect of boundary layer flow is proposed. The technique exploits the underlying dynamics of the turbulence boundary layer to generate secret key for both communication parties. Corresponding computer simulation and experiments are carried out. The bit error rate of key distribution is 0.05% and 0.22% in the simulation and the experiment, respectively. Further test also shows that the proposed key generation technique is valid to work with optical encryption technique.
Fuzzy control iterative algorithm for beam uniformity enhancement of gas laser through boundary layer flow is presented. The iterative process of the proposed algorithm is controlled by the fuzzy control theory. In each loop, the MSE and the TUI value are evaluated to fuzzily determine which one is relatively greater, leading to different approaches in the iteration. Computer simulation results proved the effectiveness of the proposed method. Gerchberg- Saxton algorithm, profile smoothing algorithm and fuzzy control iterative algorithm are applied to the diffractive optical element design for the correction of laser beam distorted by a Blausius boundary layer. Fuzzy control iterative algorithm leads to better result than Gerchberg-Saxton algorithm and profile smoothing algorithm. Both mean square error and top ununiformity index of the result obtained by fuzzy control iterative algorithm are rather low.
A novel optical security technique for safeguarding user passwords based on an optical fractal synthesizer is proposed. A validating experiment has been carried out. In the proposed technique, a user password is protected by being converted to a fractal image. When a user sets up a new password, the password is transformed into a fractal pattern, and the fractal pattern is stored in authority. If the user is online-validated, his or her password is converted to a fractal pattern again to compare with the previous stored fractal pattern. The converting process is called the fractal encoding procedure, which consists of two steps. First, the password is nonlinearly transformed to get the parameters for the optical fractal synthesizer. Then the optical fractal synthesizer is operated to generate the output fractal image. The experimental result proves the validity of our method. The proposed technique bridges the gap between digital security systems and optical security systems and has many advantages, such as high security level, convenience, flexibility, hyper extensibility, etc. This provides an interesting optical security technique for the protection of digital passwords.
An optic-electronic hybrid certificate validation technique based on Fresnel encoding is proposed. A confirming experiment has been carried out. This technique consists of two processes: encoding and decoding. During the encoding process, an original image is encoded by a computer into an encoded image, which is subsequently printed on a certificate. During the decoding process, the encoded image is extracted from the certificate and decoded optically. The experimental result proves the validity and reveals some advantages of our method. Compared with some previous works, more useful original information can be encoded in our method. The security level of our method is also enhanced by importing the Fresnel diffraction range z as another key. This paper also explores practical application of this technique.
This paper proposes the Fuzzy Control Iterative Algorithm (FCIA) for the design of diffractive optical elements for laser
beam shaping. Firstly, to improve the poor uniformity of output laser beam obtained by the G-S algorithm, we put
forward the Profile Smoothing Algorithm (PSA), which is effective in improving beam uniformity but slack in
controlling the Mean Square Error. Then we put forward the Fuzzy Control Iterative Algorithm, which combines PSA
and G-S algorithm by fuzzy control theory. Taking advantages of GS and PSA, FCIA can decrease both Mean Square
Error and nonuniformity of output beam simultaneously. Computer-designed result shows that an extremely ideal output
beam is derived by using FCIA. The Mean Square Error is 0.75%. The nonuniformity is 0.46%. And the energy
converting efficiency is up to 94.91%. This paper affords a novel algorithm for the design of diffractive optical elements
for laser beam shaping.
We have proposed an improved optic-electronic hybrid encoding technique for certificate validation based on works of
Junji Ohtsubo and Ayano Fujimoto. Corresponding experiment was carried out for substantiating our proposed method.
Our approach enhances the level of security by importing another key image, largely increasing the cipher space and
inducing a better resistance to brutal attacks. Optical experiment exhibits while the encrypted results offered is a correct
one and another licit one but contaminated by an Additive Gaussian Noise with a Standard Deviation of 0.4, the PSNR of
decrypted image is 6.87 and 6.54, respectively. Experimental results indicate the effectiveness and robustness of this
method. This paper conducts a beneficial exploration in the practical application of optical authentication technique.
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