Developing an Effective Off-the-job Training Model and an Automated Evaluation System for Thoracoscopic Esophageal Atresia Surgery.

BACKGROUND: Pediatric minimally invasive surgery requires advanced technical skills. Off-the-job training (OJT), especially when using disease-specific models, is an effective method of acquiring surgical skills. To achieve effective OJT, it is necessary to provide objective and appropriate skill assessment feedback to trainees. We aimed to construct a system that automatically evaluates surgical skills based on forceps movement using deep learning (DL). METHODS: Using our original esophageal atresia OJT model, participants were tasked with performing esophageal anastomosis. All tasks were recorded for image analysis. Based on manual objective skill assessments, each participant's surgical skills were categorized into two groups: good and poor. The motion of the forceps in both groups was used as training data. Employing this training data, we constructed an automated system that recognized the movement of forceps and determined the quality of the surgical technique. RESULTS: Thirteen participants were assigned to the good skill group and 32 to the poor skill group. These cases were validated using an automated skill assessment system. This system showed a precision of 75%, a specificity of 94%, and an area under the receiver operating characteristic curve of 0.81. CONCLUSIONS: We constructed a system that automatically evaluated the quality of surgical techniques based on the movement of forceps using DL. Artificial intelligence diagnostics further revealed the procedures important for suture manipulation. LEVELS OF EVIDENCE: Level IV.

Bile lakes in patients with biliary atresia who presented with jaundice-free native liver survival indicating the risk of subsequent liver transplantation due to various factors.

PURPOSE: The prognostic factors of subsequent liver transplantation (LT) in patients with biliary atresia (BA) who presented with jaundice-free native liver survival were investigated. METHODS: This study retrospectively reviewed patients who underwent portoenterostomy (PE) for BA. Patients with jaundice-free native liver survival at 1 year postoperatively were divided into the autologous liver survivor and liver transplant recipient groups. Peri- and postoperative data were compared between the two groups. RESULTS: Among 97 patients with BA, 29 who received LT within 1 year after PE were excluded from the analysis. Further, 48 patients currently living with native liver and 20 who received LT after 1 year postoperatively were compared. Bile lake (BL) was the strongest risk factor of LT. The risk score was 2.38 ∗ B L s c o r e + 0.00466 ∗ T B A , and the area under the receiver operating characteristic curve was 0.83. Patients with BL and those without significantly differed in terms of the native liver survival rate. Patients with BL who presented with not only cholangitis but also gastrointestinal hemorrhage and hepatopulmonary syndrome received LT. CONCLUSION: BL can cause different pathologies. Moreover, it is an evident risk factor of subsequent LT in patients with BA who are living with native liver at 1 year after PE.

Thoracoscopic primary repair is useful for esophageal atresia with tracheoesophageal fistula in neonates with low body weight.

PURPOSE: The surgical indication of thoracoscopic primary repair for esophageal atresia with tracheoesophageal fistula is under debate. The current study aimed to investigate the outcome of thoracoscopic primary repair for esophageal atresia with tracheoesophageal fistula in patients weighing < 2000 g and those who underwent emergency surgery at the age of 0 day. METHODS: The surgical outcomes were compared between patients weighing < 2000 g and those weighing > 2000 g at surgery and between patients who underwent surgery at the age of 0 day and those who underwent surgery at age ≥ 1 day. RESULTS: In total, 43 patients underwent thoracoscopic primary repair for esophageal atresia with tracheoesophageal fistula. The surgical outcomes according to body weight were similar. Patients who underwent surgery at the age of 0 day were more likely to develop anastomotic leakage than those who underwent surgery at the age of ≥ 1 day (2 vs. 0 case, p = 0.02). Anastomotic leakage was treated with conservative therapy. CONCLUSION: Thoracoscopic primary repair is safe and useful for esophageal atresia with tracheoesophageal fistula even in newborns weighing < 2000 g. However, emergency surgery at the age of 0 day should be cautiously performed due to the risk of anastomotic leakage.

Update on aortopexy and posterior tracheopexy for tracheomalacia in patients with esophageal atresia.

Despite improving the survival after repair of esophageal atresia (EA), the morbidity of EA repair remains high. Specifically, tracheomalacia (TM) is one of the most frequent complications of EA repair. Continuous positive airway pressure is generally applied for the treatment of TM. However, surgical intervention is required against an apparent life-threatening event or inability to perform extubation for a long period. According to our review, most cases of TM showed symptom improvement after aortopexy. The ratio of the trachea's lateral and anterior-posterior diameter at the brachiocephalic artery crossing the trachea, which reflects the compression of the trachea by the brachiocephalic artery, is a good indicator of aortopexy. Our finding suggests that most TM cases associated with EA may not be caused by tracheal fragility alone, but may involve blood vessel compression. Posterior tracheopexy (PT) is also an effective treatment for TM. Recently, open or thoracoscopic PT was able to be performed simultaneously with EA repair. In many cases, aortopexy or PT is a safe and effective surgical treatment for TM with EA. Other surgical procedures, such as external stenting, should be considered for patients with diffuse-type TM for whom aortopexy and PT appear relatively ineffective.

Surgical Strategies for Neonates with Prenatally Diagnosed Congenital Biliary Dilatation.

BACKGROUND: This study aimed to develop a postnatal treatment strategy for infants with prenatally diagnosed congenital biliary dilatation. METHODS: We performed a retrospective study of patients with prenatal diagnosed congenital biliary dilatation (CBD), aged <1 year who underwent surgery at our hospital between 2013 and 2023. We classified the patients into two groups, the "early group," consisting of patients who could not wait for growth, and required early surgery, and the "scheduled group," consisting of patients who were asymptomatic and could undergo scheduled surgery, and compared them. The parameters for early surgical prediction were AST, ALT, TB, DB, and CRP levels at birth, 1 week, 2 weeks, 1 month, 2 months, and 3 months after birth, and immediately before surgery, as well as the cyst diameter, presence of intrahepatic bile duct dilation, and presence of debris in the common bile duct. RESULTS: During the study period, 15 patients were diagnosed prenatally. The cyst diameter was significantly larger at all points in the early group. Patients with a cyst diameter of >30 mm at birth, intrahepatic bile duct dilatation at birth, and postnatal enlargement of the common bile duct to >30 mm are more likely to develop symptoms early. Blood biochemistry tests showed no significant differences between the two groups. CONCLUSIONS: Patients with a cyst diameter >30 mm in the early postnatal period require careful postnatal management and parents should be counseled regarding the high likelihood of their child needing surgery within the first 3 months of life. LEVEL OF EVIDENCE: Level IV.

Safe thoracoscopic repair of recurrent congenital diaphragmatic hernia after initial open abdominal repair.

PURPOSE: The optimal surgical approach for recurrent congenital diaphragmatic hernia (CDH) remains controversial. We compared the surgical outcomes of a thoracoscopic approach versus an open abdominal approach for recurrent CDH after initial abdominal open repair. METHOD: The subjects of this comparative study were patients who underwent open abdominal or thoracoscopic surgery for recurrent CDH following an initial open abdominal repair. RESULTS: Among 166 patients with Bochdalek-type CDH, 15 underwent reoperation for recurrent CDH following an open abdominal repair. Seven patients underwent open abdominal surgery (group O) and eight underwent thoracoscopic surgery (group T). The operative duration was similar for the two groups, with less blood loss (17.2 ml/kg vs. 1 ml/kg, P = 0.001) and fewer intraoperative complications in the T group (n = 6 vs. n = 0 cases, P = 0.001). There was no significant difference in the number of postoperative complications (n = 1 vs. n = 1, P = 1.0) or in the number of patients with a second CDH recurrence (n = 2 vs. n = 1, P = 0.569) between the two groups. CONCLUSION: Thoracoscopic surgery is preferable to the open surgical approach for recurrent CDH following an initial abdominal open repair.

Robotic versus laparoscopic radical surgery for pediatric congenital biliary dilatation: a comparison of surgical outcomes of a single surgeon's initial experience.

PURPOSE: This study aimed to clarify the validity of robot-assisted surgery (RAS) for pediatric patients with congenital biliary dilatation (CBD). METHODS: We retrospectively compared RAS and laparoscopic surgery (LS) for pediatric CBD performed by the same certified surgeon between 2016 and 2022. RESULTS: We included 6 RAS and 12 LS cases in this study. One case of RAS with laparotomy was excluded from the analysis. The patients in the two groups had comparable ages and body weights. The median surgery duration, the suture time per stitch, and the time to drain removal were 385 min, 145 s, and 5 days in the RAS group and 370 min (p = 0.28), 177 s (p = 0.03), and 6 days (p = 0.03) in the LS group, respectively. The time to create the Roux-en-Y limb was significantly longer in the RAS group. Postoperative complications occurred in one RAS case and in four LS cases. CONCLUSIONS: Less anastomotic time per stitch and less time to drain removal suggest that RAS may contribute to accurate suturing and fine intra-pancreatic bile duct dissection. In addition, RAS requiring large movements of forceps in a large surgical field, such as Roux-en-Y creation, is inferior to LS.

Preoperative Contrast Examinations Help Determine the Appropriate Cervical Approach for Congenital Gross Type C Esophageal Atresia: A Report of Two Cases.

BACKGROUND Kluth demonstrated that esophageal atresia/tracheoesophageal fistula (EA/TEF) has several anatomical variations and thus requires a preoperative imaging study to determine the surgical strategy. We routinely perform a contrast examination with iodixanol to assess the location of the TEF and the upper end of the esophageal pouch to determine the most appropriate approach. We herein present two cases of type C EA/TEF who successfully underwent radical surgery by a cervical approach based on the information from the contrast examination. CASE REPORT Case 1 was a Japanese boy suspected of type C EA/TEF after birth. A contrast examination with iodixanol showed that a TEF was at the second thoracic vertebra (Th2), as was the upper end of the esophageal pouch. Thus, the patient underwent esophago-esophageal anastomosis and TEF ligation using a cervical approach; the postoperative course was uneventful. Case 2 was also a Japanese boy suspected of type C EA/TEF. A contrast examination showed that the TEF was at Th1-2, as was the upper end of the esophageal pouch. Thus, the patient underwent esophago-esophageal anastomosis and TEF ligation using a cervical approach. The patient suffered from congenital tracheal stenosis and required tracheoplasty. However, there were no apparent complications after the surgery. CONCLUSIONS Here, we used the imaging information to adopt the cervical approach in type C EA/TEF cases and concluded that routine preoperative contrast examinations helped assess the TEF location and upper end of the esophageal pouch without significant complications.

Anastomotic time was associated with postoperative complications: a cumulative sum analysis of thoracoscopic repair of tracheoesophageal fistula in a single surgeon's experience.

PURPOSE: This study aimed to evaluate the learning curve of thoracoscopic repair of tracheoesophageal fistula (TEF) by a single surgeon using a cumulative sum (CUSUM) analysis. METHODS: Prospective clinical data of consecutive Gross type-C TEF repairs performed by a pediatric surgeon from 2010 to 2020 were recorded. CUSUM charts for anastomosis and operating times were generated. The learning curves were compared with the effect of accumulation based on case experience. RESULTS: For 33 consecutive cases, the mean operative and anastomosis times were 139 ± 39 min and 3137 ± 1110 s, respectively. Significant transitions beyond the learning phase for total operating and anastomosis times were observed at cases 13 and 17. Both the total operating time and anastomosis time were significantly faster in the proficiency improvement phase than in the initial learning phase. Postoperative complications significantly decreased after the initial anastomosis learning phase but not after the initial total operating learning phase. CONCLUSIONS: Thoracoscopic repair of TEF is considered safe and feasible after 13 cases, where the surgeon can improve their proficiency with the total operation procedure, and 17 cases, which will enable the surgeon to achieve proficiency in anastomosis. Postoperative complications significantly decreased after gaining familiarity with the anastomosis procedure through the learning phase.

Management of Congenital and Postoperative Chylothorax: Use of Thoracoscopic Lymphatic Leak Ligations with Intraoperative ICG Lymphangiography.

BACKGROUND: Congenital chylothorax (CCT) and postoperative chylothorax (POCT) are rare and difficult to treat. We report our treatment strategy and outcomes for chylothorax, including thoracoscopic surgery with indocyanine-green (ICG) near-infrared fluorescence lymphangiography. METHODS: A retrospective review of patients with CCT and POCT from 2014 to 2021 was performed. After definitive diagnosis, conservative treatments with octreotide, followed by intravenous steroids as needed, were performed. Patients who were refractory to conservative treatment were transferred to surgical treatment, consisting of thoracoscopic lymphatic leak ligations using ICG intraoperative lymphangiography. The effectiveness of conservative and surgical treatment was then examined. RESULTS: We included 19 cases of CCT and 31 cases of POCT. The 31 POCT patients included 23 of 84 postoperative patients with congenital diaphragmatic hernia (CDH), 7 of 54 postoperative patients with esophageal atresia (EA), and 1 of 3 postoperative patients with lymphatic malformation. The efficacy of conservative treatment was 12/19 for CCT, 22/23 for CDH, and 4/7 for EA. Surgical intervention was performed in 10 patients, and the rate of resolution of chylothorax within 3 weeks after surgery was 90%. CONCLUSION: Thoracoscopic lymphatic leak ligations with intraoperative ICG lymphangiography are feasible and useful in patients with chylothorax refractory to conservative treatment. LEVEL OF EVIDENCE: Level IV.

Laparoscopic bile duct plasty for hilar bile duct stenosis (HBDS) in patients with congenital biliary dilatation: Diagnosis of HBDS by preoperative MRCP and laparoscopic strategy to relieve HBDS.

BACKGROUND/PURPOSE: Congenital biliary dilatation (CBD) is a disease associated with pancreaticobiliary maljunction. The most frequent postoperative complication is intrahepatic stones, which are caused by hilar bile duct stenosis (HBDS). METHODS: We retrospectively reviewed the records of patients who underwent primary surgery for CBD between 2013 and 2021. We evaluated images and videos of HBDS, the laparoscopic technique of releasing the stenosis, and its occurrence rate and compared intraoperative bile duct findings with those of preoperative magnetic resonance cholangiopancreatography (MRCP). RESULTS: There were 87 CBD cases in this study. HBDS occurred in 52% and preoperative MRCP for HBDS showed a 96% sensitivity and 74% specificity in this study. Bile duct plasty was performed in 45% of the cases and videos demonstrated typical methods of laparoscopic bile duct plasty. The mid- to long-term complications were hepatolithiasis in three patients, anastomotic site stricture in three, and postoperative obstruction in two. CONCLUSIONS: Our study revealed that preoperative imaging studies are useful for the prediction of HBDS. Our laparoscopic meticulous probing method for finding BDS reveals more intrahepatic BDS through magnification. Therefore, this may reduce the incidence of intrahepatic stones. Preoperative imaging and intraoperative findings can be complemented to plan management that reduces long-term complications.

Laparoscopic internal intestinal drainage of bile lakes in a patient with recurrence of jaundice after laparoscopic revision of Kasai portoenterostomy for biliary atresia: A case report.

Bile lake, of the postoperative complications after Kasai portoenterostomy (PE) for biliary atresia, causes cholangitis that may induce progressive fibrosis of the liver. Standard treatment for bile lakes has not yet been established, but there are reports that surgical internal intestinal drainage for bile lakes effectively prevents cholangitis and maintains jaundice-free status. In this case, insertion of the percutaneous transhepatic biliary drainage into the bile lake allowed continuous drainage of large volumes of bile juice. However, reoperation following laparotomy increases the surgical risk of subsequent liver transplantation due to postoperative adhesion. Laparoscopic surgery was selected for the patient who was likely to require liver transplantation in the future. In this case, laparoscopic internal intestinal drainage of bile lakes was performed safely by a Cavitron ultrasonic surgical aspirator for the recurrence of jaundice after laparoscopic revision of PE. Cholangitis and jaundice were rapidly resolved after this surgical procedure.

Rare case of a right Bochdalek hernia with retroperitoneal prolapse of organs into the thoracic cavity in infancy: A case report.

We report an extremely rare case of a right Bochdalek hernia with a sac, in which the retroperitoneal and intra-abdominal organs prolapsed into the thoracic cavity at the same time. The patient was a 7-month-old female with no comorbidities. She presented with cough and fever, and chest radiography revealed a right diaphragmatic hernia. Computed tomography showed that the right kidney, intestine, colon, and liver had prolapsed into the thoracic cavity. The patient underwent thoracoscopic surgery, which showed that the abdominal and retroperitoneal organs prolapsed into the thoracic cavity through the Bochdalek hernia. The herniated organs were spontaneously reduced using thoracoscopic insufflation. The defect hole was closed with artificial mesh. We adopted a thoracoscopic approach, in terms of easy reduction of herniated organs and accurate evaluation of the hernia orifice, which was useful.

Biochemical markers to predict the development of gastrointestinal bleeding and esophageal varices after portoenterostomy in biliary atresia.

PURPOSE: Gastrointestinal bleeding (GIB) due to esophageal varices (EV) is one of the factors that negatively impact native liver survival of patients with biliary atresia (BA). Gastrointestinal fibroscopy (GIF) is usually used to determine the presence of EVs; however, it requires general anesthesia. The aim of this study is to search for markers in blood tests obtained during routine check-ups that can predict the development of GIB. METHODS: Data of patients with BA who underwent portoenterostomy at our hospital from 2014 to 2020 were retrospectively reviewed. The patients' data were assigned to three groups according to specific time points: Group B, which included data at GIB; Group NB-T, which included data at GIF and EV treatment; and Group NB-NT, which included data at GIF without treatment. The data in Group B were compared to those of other groups. RESULTS: In our study, GIB occurred in 11 patients, and 12 cases and 8 cases were classified into Groups NB-NT and NB-T, respectively. Compared with the other groups, only ChE and M2BPGi in Group B showed statistically significant differences. CONCLUSIONS: ChE and M2BPGi are useful for predicting GIB.

Refractory tracheoesophageal fistula treated using multi-stage surgery: A case report.

A tracheoesophageal fistula (TEF) recurs in approximately 2%-13% of cases of esophageal atresia with TEF that are treated surgically. Currently, there is no consensus on the most effective treatment to prevent recurrent TEF (RTEF). Herein, we present a patient with type C esophageal atresia who underwent thoracoscopic esophago-esophageal anastomosis and TEF repair at 2 days old. However, RTEFs were observed at ages 3, 6, and 11 months, and thoracoscopic TEF repairs using a pleural patch, fascia lata graft, and pectoralis major myocutaneous (PMMC) flap were performed, respectively. A fourth recurrence led to mediastinitis, shock liver, disseminated intravascular coagulopathy, and a compromised respiratory status. Hence, laparoscopic esophageal transection was first performed to improve the respiratory condition by preventing the regurgitation of gastric contents. Once the patient was stable, a subtotal esophageal resection with TEF closure followed by gastric tube reconstruction was performed. In conclusion, we encountered a case of refractory RTEF that was repaired four times using various techniques, including a fascia lata graft and PMMC flap. However, TEF still recurred after these four operations. The final surgical strategy involved an esophageal transection as a palliative therapy, which improved the respiratory condition, followed by closure of the TEF and subtotal esophageal resection. Finally, esophageal reconstruction using a gastric tube after the complete remission of inflammation was effective. This multi-stage surgery was considered the only choice to rescue the patient and effectively prevent another recurrence.

Aberrant branches of the subclavian artery and their relationship with the phrenic nerve and the brachial plexus / Ramas aberrantes de la arteria subclavia y su relación con el nervio frénico y el plexo braquial

SUMMARY: Variations in subclavian artery branches are relatively common and may impact surgical procedures and effects. During educational dissection of a male cadaver, we encountered an extremely rare variation of the right subclavian artery branches. The internal thoracic artery, the thyrocervical trunk, and the costocervical trunk arose from the third part of the right subclavian artery. In addition, the phrenic nerve displaced remarkably laterally by the thyrocervical trunk, and the course of the costocervical trunk was between the upper trunk and the middle trunk of the brachial plexus. These variations may pose a potential risk for nerve compression and increase the risk of arterial and nerve puncture. This case report would bring attention to the possibility of other similar cases, and early detection of these variations through diagnostic interventions is helpful to reduce postoperative complications.

RESUMEN: Las variaciones en las ramas de la arteria subclavia son relativamente comunes y pueden afectar los procedimientos y efectos quirúrgicos. Durante la disección educativa de un cadáver masculino, encontramos una variación extremadamente rara de las ramas de la arteria subclavia derecha. La arteria torácica interna, el tronco tirocervical y el tronco costocervical nacían de la tercera parte de la arteria subclavia derecha. Además, el nervio frénico se desplazaba lateralmente por el tronco tirocervical, y el trayecto del tronco costocervical se encontraba entre el tronco superior y el tronco medio del plexo braquial. Estas variaciones pueden suponer un riesgo potencial de compresión nerviosa y aumentar el riesgo de punción arterial y nerviosa. Este reporte de caso llamaría la atención sobre la posibilidad de otros casos similares, y la detección temprana de estas variaciones a través de diagnósticos es útil para reducir las complicaciones postoperatorias.

Band alignments and heterostructures of monolayer transition metal trichalcogenides MX3 (M = Zr, Hf; X = S, Se) and dichalcogenides MX2 (M = Tc, Re; X=S, Se) for solar applications.

Knowledge of band alignments and heterostructure formations is fundamental for a new generation of optoelectronics based on two-dimensional layered materials. Herein, band alignments and heterostructures of IVB-VIA monolayer MX3 (M = Zr, Hf; X = S, Se) and VIIB-VIA monolayer MX2 (M = Tc, Re; X = S, Se) are calculated by density functional theory with hybrid functionals. The results indicate that for monolayer MX3, the valence bands mainly depend on the p state of the chalcogens and the conduction bands mainly depend on the d state of the transition metals. In contrast, for monolayer MX2, both valence and conduction bands depend on the d state of the transition metals. This suggests that their work functions are obviously different. Meanwhile, the characteristics of the band alignments and the planar-averaged local density of states show that ZrS3, HfS3, TcSe2 and ReS2 could be favorable candidates for photocatalytic water splitting. ZrS3, HfS3 and MX2 with the same structures are able to form type II heterostructures at their interfaces, which could be used for solar energy conversion. The power-conversion efficiency of an MX3 thin-film solar cell is approximately 16-18%, which is higher than those of MX2 thin-film solar cells. In addition, for heterostructures composed of MX3, both of the two kinds of material (M and X) play an important role in every band formation. Meanwhile, for MX2 heterostructures, almost every band depends only on a single material. The charge density difference of the heterostructures demonstrates a higher charge accumulation at the interface of MX3 heterostructures than that of MX2 heterostructures. These phenomena show that type II heterostructures formed of MX3 are more stable than those of MX2.

Efficient mixed-solvent exfoliation of few-quintuple layer Bi2S3 and its photoelectric response.

A scalable liquid exfoliation of layered Bi2S3 employing a mixed-solvent strategy was used for the fabrication of Bi2S3 nanosheets. We found that 10% deionized water in 90% isopropyl alcohol is the best mixed solvent for the efficient and effective exfoliation of layered Bi2S3. These results are consistent with the absorbance spectra and enthalpy of mixing theory. The obtained Bi2S3 nanosheets had few-quintuple layers and were investigated by transmission electron microscopy, atomic force microscopy, and Raman spectroscopy. These Bi2S3 nanosheets can be used to fabricate large-scale thin films by filtration method; the films demonstrated sensitive photoelectric response with the rise and decay response of photocurrent on the sub-second scale under visible light excitation. The electronic structures of bulk and one-quintuple layer Bi2S3 are calculated by first-principle calculation for better understanding of the photoelectric response. A green mixed-solvent processing of Bi2S3 opens up the potential application of Bi2S3 optoelectric films to photoelectric detection and solar energy conversion devices.

Resonance Rayleigh scattering methods for the determination of chitosan with Congo red as probe.

Two methods were presented for the sensitive and selective determination of chitosan (CTS) with Congo red (CR) as probe based on resonance Rayleigh scattering (RRS) intensities in health products. In weakly acidic buffer solution, the binding of CTS to CR, could result in the enhancement of the RRS intensities. Moreover, after adding OP emulsifier (octyl-phenyl polyoxyethylene ether) to the system, the RRS intensities showed more significantly enhancement. The maximum RRS signals for the CTS-CR system and the CTS-CR-OP system were located at 380 nm and 376 nm, respectively. Under optimum experimental conditions, the increased RRS intensities (ΔI) of these two systems were linear to CTS concentration in the range of 0.40-8.00 µg/ml and 0.05-1.00 µg/ml. Their limits of detection (LOD) were 44.81 ng/ml and 6.99 ng/ml, which indicated that the latter system was more sensitive than the former. In this work, the optimum conditions and the effects of some foreign substances on the determination were studied. In addition, the effect of the molecular weight of CTS and the reasons for the enhancement of resonance light scattering were discussed. Finally, these two methods were applied to the determination of chitosan in health products with satisfactory results.

Surface Optical Rectification from Layered MoS2 Crystal by THz Time-Domain Surface Emission Spectroscopy.

Surface optical rectification was observed from the layered semiconductor molybdenum disulfide (MoS2) crystal via terahertz (THz) time-domain surface emission spectroscopy under linearly polarized femtosecond laser excitation. The radiated THz amplitude of MoS2 has a linear dependence on ever-increasing pump fluence and thus quadratic with the pump electric field, which discriminates from the surface Dember field induced THz radiation in InAs and the transient photocurrent-induced THz generation in graphite. Theoretical analysis based on space symmetry of MoS2 crystal suggests that the underlying mechanism of THz radiation is surface optical rectification under the reflection configuration. This is consistent with the experimental results according to the radiated THz amplitude dependences on azimuthal and incident polarization angles. We also demonstrated the damage threshold of MoS2 due to microscopic bond breaking under the femtosecond laser irradiation, which can be monitored via THz time-domain emission spectroscopy and Raman spectroscopy.