Microwave optical limiting via an acoustic field in a diamond mechanical resonator.

We investigate the generation and control of the reverse saturable absorption (RSA) and optical limiting (OL) at microwave (mw) range in high-Q single-crystal diamond mechanical resonator (DMR) embedded with many nitrogen-vacancy (NV) centers. The strain-induced acoustic modes enable mechanical manipulation of NV centers. On the basis of strain-coupling mechanism, it is shown that the saturable absorption (SA) switches to the RSA by applying the acoustic field, leading to induce the OL in the diamond through the cross-Kerr effect. We demonstrate that the OL characteristics such as, threshold, efficiency, and dynamic range can be controlled by changing either the intensity or frequency of the acoustic field. Moreover, we show that this optical limiter can amplify noiselessly the low intensity of the mw field input to the sensors and also attenuate any gain-induced noise and increase in the intensity of the mw field if it exceeds the intensity threshold. In addition, it is shown that by increasing either the number of NV centers or length of the diamond, the optical limiter can be more efficient. The physical mechanism of the OL establishment is explained using the analytical expressions, which are in good agreement with the numerical results. Our proposed acoustic-induced optical limiter can be a scheme for protecting different optical and electronic devices in mw range, remote sensing, navigation, communications, microwave heating and thermo/laser therapy.

Laguerre-Gaussian modes generated vector beam via nonlinear magneto-optical rotation.

Laguerre-Gaussian (LG) beams contain a helical phase front with a doughnut-like intensity profile. We use the LG beam to introduce a rather simple method for generation of a vector beam (VB), a beam with spatially-dependent polarization in the beam cross section, via the nonlinear magneto-optical rotation (NMOR). We consider the NMOR of the polarization of a linearly polarized probe field passing through an inverted Y-type four-level quantum system interacting with a LG control field and a static magnetic field. It is shown that the polarization of the transmitted field is spatially distributed by the orbital angular momentum (OAM) of the LG control field, leading to generation of the VB with azimuthally symmetric polarization distribution. We show that the polarization and intensity distributions of the VB spatially vary by changing the OAMs of the LG control field. Moreover, the radial index of the LG control field has a major role in more spatially polarization distributing of the VB. It is shown that the intensity of the generated VBs in different points of the beam cross section can be controlled by the OAM as well as the radial index of the LG control field. However, the VB with highly spatially distributed can be generated for higher values of the radial index of LG control field. The analytical calculations determine the contribution of the different nonlinear (cross-Kerr effect) phenomena on the generation of the VB. We show that the VB is mainly generated via birefringence induced by the applied fields. Finally, we use asymmetric LG (aLG) beams for making the VBs with asymmetric polarization distribution. It is shown that by applying aLG beams, the azimuthal symmetry of the polarization distribution breaks and the asymmetric polarization distribution can be controlled by OAM and radial index of the aLG control field. The obtained results may find more interesting applications in fiber/free space optical communication to enhance the capacity of the information transmission.

Acoustic field induced nonlinear magneto-optical rotation in a diamond mechanical resonator.

We study the nonlinear magneto-optical rotation (MOR) of a linearly polarized microwave probe field passing through many nitrogen-vacancy (NV) centers embedded in a high-Q single-crystal diamond mechanical resonator. On the basis of the strain-mediated coupling mechanism, we establish a three-level closed-loop system in the ground states of the NV center in the presence of a static magnetic field. It is shown that by applying an acoustic field, the birefringence is induced in the system through the cross-Kerr effect, so that the probe field is transmitted with a high intensity and rotated polarization plane by 90 degrees. In addition, we demonstrate that the acoustic field has a major role in enhancing the MOR angle to 90 degrees. Moreover, it is shown that the MOR angle of the polarization plane after passing through the presented system is sensitive to the relative phase of the applied fields. The physical mechanism of the MOR enhancement is explained using the analytical expressions which are in good agreement with the numerical results. The presented scheme can be used as a polarization converter for efficient switching TE/TM modes in optical communication, the depolarization backscattering lidar, polarization spectroscopy and precision measurements.

Coherent control of Optical limiting in atomic systems.

Generation and control of the reverse saturable absorption (RSA) and optical limiting (OL) are investigated in a four-level Y-type quantum system. It is demonstrated that the applied laser fields induce the RSA and it can be coherently controlled by either intensity or frequency of the applied laser fields. The effect of the static magnetic field on the induced RSA is studied and we obtain that it has a constructive role in determining the intensity range in which the OL is established in the system. In addition, we find that the transmission of the suggested optical limiter can be decreased either by increasing the length of the medium or by getting the atomic system denser. Finally, the Z-scan technique is presented to confirm our theoretical results. The proposed scheme can be used in designing the coherent optical limiters with controllable threshold and intensity range of the OL.

Enhanced nonlinear magneto-optical rotation in cold atoms: A theoretical study.

We theoretically investigate magneto-optical rotation (MOR) of a linearly polarized probe field in the four-level N-type cold atoms. By applying a static magnetic field and a weak coupling field, it is shown that the birefringence enhancement is induced in the system. Moreover, we show that the static magnetic field has a major role in switching the dichroism to enhanced birefringence in the system. We also obtain a large intensity for the output field with nearly perpendicular MOR angle by 88 degrees with subnatural width. It is demonstrated that Doppler broadening has a destructive effect on the MOR of the polarization direction of the probe field. The results of our study can be used for selecting narrow band of wavelengths and polarization converter for efficient switching of TM/TE polarization modes in optical communication, the depolarization backscattering lidar, polarization spectroscopy and precision measurements.

Sacroiliac Joint Intraarticular Injection in True Anteroposterior View: Description of a New C-Arm Guided Method.

BACKGROUND: The anatomic characteristics of the sacroiliac joint (SIJ) make it difficult to achieve intraarticular injection without radiologic guidance. The classic C-arm guided SIJ intervention technique is difficult. Here we describe a new and simple method for SIJ intraarticular intervention. OBJECTIVE: This study aims to introduce a new, simple approach for SIJ intraarticular intervention. STUDY DESIGN: An observational case series study. SETTING: The study was conducted at an academic medical center in a major metropolitan city. METHODS: This method of intervention was performed on 57 patients (a total of 73 joints) who were selected for diagnostic and therapeutic SIJ intervention. The procedure was done in anteroposterior (AP) view, without any C-arm angulation. The accuracy of the intraarticular injection was confirmed by using intraarticular contrast material. A numerical rating scale (NRS) score was recorded for each joint before and after the procedure; the number of x-ray exposures and number of attempts were recorded for each procedure as well. RESULTS: Successful intraarticular contrast spread was obtained in all SIJs. The number of x-ray exposures was about 9 ± 3, and there was not a remarkable difference between cases according to gender of the patient (P = 0.1) or side of the joint (P = 0.2). In 5 cases, the first needle placement was not correct; there were no differences between gender (P = 0.4) and side of the joint (P = 0.4) regarding the first successful attempt. The NRS pain scores decreased in all of the patients more than 50% after the procedure; the pain scores were similar to the results of classic methods of intraarticular interventions with successful contrast spread, and there were no remarkable differences considering gender (P = 0.5) or side of the joint (P = 0.8). LIMITATIONS: This is a very small, nonrandomized, and controlled study; further blinded clinical trials are needed to clarify the probable advantages of this method compared with conventional ones. CONCLUSION: This observational study introduces a new and simple approach for SIJ intraarticular intervention, with a high success rate. KEY WORDS: Low back pain, sacroiliac joint, C-arm, new technique, intraarticular, injection.

Survival after judicial hanging.

Hanging is known not only as a common method of suicide but also as a capital punishment method in some countries. Although several cases have been reported to survive after the attempted suicidal/accidental hanging, to the extent of our knowledge, no modern case of survival after judicial hanging exists. We reported a case of an individual who revived after modern judicial hanging despite being declared dead. The case was admitted with poor clinical presentations and the Glasgow Coma Scale of 6/15. The victim received all the standard supportive intensive care and gained complete clinical recovery.

Predicting difficulty score for spinal anesthesia in transurethral lithotripsy surgery.

BACKGROUND: Spinal anesthesia (SA) is the most common regional anesthesia (RA) conducted for many surgical procedures. OBJECTIVES: The current study aimed to predict the difficulty score of SA, by which to reduce the complications and ultimately improve the anesthesia quality. MATERIALS AND METHODS: Transurethral Lithotripsy (TUL) surgery candidates were enrolled in this observational study from 2010 to 2011. Before SA, the patient`s demographic information along with the Body Mass Index (BMI), lumbar spinous process status, spinal deformity, radiological signs of lumbar vertebrae, and a history of spinal surgery or difficult SA were recorded, then the patients underwent SA in L3-L4 interspinous process space. Information about Cerebrospinal Fluid (CSF) visibility at the first attempt (easy SA) and the times of trying with shifting in that space or trying the second space (moderate SA) and the third space (difficult SA) were recorded. Multinominal regression and relative operating characteristic (ROC) curve were used for statistical analysis. RESULTS: Hundred and one patients were enrolled. Of these patients, 50 (49.5%) underwent SA by the first attempt of the first space, in 36 patients (35.6%) it was moderate and in 15 patients (14.9%) it was difficult. There was no significant relationship between difficulty score of SA and gender, age, height, and history of previous difficult SA. But there was a significant relationship between difficulty score of SA and lumbar spinous process status (P =0.0001), radiological profile of the lumbar spine (P = 0.0001), the status of lumbar deformity (P = 0.007), and BMI (P = 0.006). Then using the ROC curve to predict the difficult SA, the cutoff point was 8.5 with 86.7% and 86% sensitivity and specificity, respectively. CONCLUSIONS: It seems that considering the clinical examination of patients before SA focusing on lumbar spinous process status, presence of lumbar deformity, calculation of BMI and radiological signs of lumbar vertebrae can be helpful in predicting SA difficulty.