This paper reports that a one-colour fs pump probe measurement has been carried out for studying photoionization/photodissociation of cyclohexanone （C6H10O） in intense laser field. Two of the fragments from eyclohex...This paper reports that a one-colour fs pump probe measurement has been carried out for studying photoionization/photodissociation of cyclohexanone （C6H10O） in intense laser field. Two of the fragments from eyclohexanone, C2H＋ and C3H3＋, are studied under 800 nm laser pump-probe and the results obtained show similar time evolutions. It proposes a feasible model for analysing the experimental observations of the one-colour fs pump-probe measurement. The results demonstrate that as an intermediate product, the excited molecular parent ions play a very important role in photionization/photodissociation processes in intense laser field.展开更多
In this work,we simulated 2D infrared spectroscopy(IR)spectroscopy in both transmission geometry and Brewster-angle reflection geometry.Light dispersion and the leakage of s-polarized light are considered in simulatin...In this work,we simulated 2D infrared spectroscopy(IR)spectroscopy in both transmission geometry and Brewster-angle reflection geometry.Light dispersion and the leakage of s-polarized light are considered in simulating the enhancement factor of the reflection mode.Our simulation shows that the dispersion in reflection will only alter the 2D IR lineshape slightly and can be corrected.Leaking spolarized light due to imperfectness of IR polarizers in the reflection geometry may limit the enhancement factor,but such limit is above what a typical experiment can reach.In the current experiment,the enhancement factor is mainly limited by the precision of incident angle,for which ordinary rotation stages are probably not adequate enough.Moreover,traditional energy ratio of pump and probe pulses,which is 9:1,may not be ideal and could be changed to 2:1 in the reflection geometry.Considering all the above factors,the enhancement on the order of 1000 is possible in the current experiment.Nevertheless,near-Brewster angle reflection will enhance both the signal and the noise caused by the signal itself,therefore this method only works if the noise is unrelated to the signal,particularly if the noise is caused by the fluctuation in the probe.It cannot improve the signal to noise ratio when the dominate noise is from the signal itself.The theoretical results here agree reasonably well with published experiment results and pave way for realizing even higher enhancement at nearer-Brewster angle.展开更多
We present new diagnostics for use in optical laser pump-X-ray Free Electron Laser(XFEL)probe experiments to monitor dimensions,intensity profile and focusability of the XFEL beam and to control initial quality and ho...We present new diagnostics for use in optical laser pump-X-ray Free Electron Laser(XFEL)probe experiments to monitor dimensions,intensity profile and focusability of the XFEL beam and to control initial quality and homogeneity of targets to be driven by optical laser pulse.By developing X-ray imaging,based on the use of an LiF crystal detector,we were able to measure the distribution of energy inside a hard X-ray beam with unprecedented high spatial resolution(~1 mm)and across a field of view larger than some millimetres.This diagnostic can be used in situ,provides a very high dynamic range,has an extremely limited cost,and is relatively easy to be implemented in pump-probe experiments.The proposed methods were successfully applied in pump-probe experiments at the SPring-8 Angstrom Compact free electron LAser(SACLA)XFEL facility and its potential was demonstrated for current and future High Energy Density Science experiments.展开更多
Opto-thermal relaxation is one of the most important properties of nonlinear optical materials.Rapid and high precision measurement of this parameter is vital in both fundamental research and applications.Current meas...Opto-thermal relaxation is one of the most important properties of nonlinear optical materials.Rapid and high precision measurement of this parameter is vital in both fundamental research and applications.Current measurement uses either complicated structure with poor precision or high power heating source with low efficiency.Here,we propose a pump-probe method(PPM) to optically measure the thermal relaxation using whispering gallery mode(WGM) microcavities.When the pump laser shines on a microcavity,the materials absorb the input power resonantly and heat up.Then the heat dissipates from the cavities to the surroundings.The opto-thermal effect induces a refractive index change reflected in the signal light transmission spectra.By analyzing the curve character of the transmission spectra of the signal response in the spontaneous relaxation process,the thermal relaxation time can be rapidly measured with high precision.Additionally,we systematically verify the PPM using microtoroids under various pump powers and at various locking points of the signal laser mode.The small rate of refractive index changes($10à8) can be discerned with an input pump power as low as 11.816 l W.Hence,the PPM can be used to detect refractive index perturbation,like gas or liquid sensing,temperature fluctuations with ultra-high sensitivity and be applied to optical materials analysis efficiently.展开更多
Pump-probe differential reflection and transmission spectroscopy is a very effective tool to study the nonequilibrium carrier dynamics of graphene. The reported sign of differential reflection from graphene is not exp...Pump-probe differential reflection and transmission spectroscopy is a very effective tool to study the nonequilibrium carrier dynamics of graphene. The reported sign of differential reflection from graphene is not explicitly explained and not consistent. Here, we study the differential reflection and transmission signals of graphene on a dielectric substrate. The results reveal the sign of differential reflection changes with the incident direction of the probe beam with respect to the substrate. The obtained theory can be applied to predict the differential signals of other two-dimensional materials placed on various dielectric substrates.展开更多
The photodissociation/photoionization processes of chlorobromomethane (CH_2BrCl) induced by fem- tosecond laser pulses have been investigated using pump-probe scheme combined with the time-of-flight mass spectra. The ...The photodissociation/photoionization processes of chlorobromomethane (CH_2BrCl) induced by fem- tosecond laser pulses have been investigated using pump-probe scheme combined with the time-of-flight mass spectra. The dominate photoproducts are observed at different delay time of the pump (400 nm) and probe (800 nm) pulses and the corresponding time-dependence of them is obtained. The results show that the decaying time of the molecule CH_2BrCl in the A-band is in the 100 fs. The decaying tendencies of the fragment ions (CH_2Cl^+ and CH_2Br^+) and the parent ion (CH_2BrCl^+) are almost the same and the relative ratios of the yields of them keep constant during the delay time of 0 to 150 fs. These facts suggest that the fragment ions come from the fragmentation of the parent ions in excited electronic states. The probabilities to form CH_2Cl^+ and CH_2Br^+ are obtained from the relative ratio of the ion intensity and are about 71.6% and 14.2%, respectively.展开更多
The ultrafast dynamics and dissociative ionization of CS2 were studied using the pump-probe method with time-of-flight mass spectroscopy. The transient behavior of both parent ion (CS2+) and fragment ions (S+ and CS+)...The ultrafast dynamics and dissociative ionization of CS2 were studied using the pump-probe method with time-of-flight mass spectroscopy. The transient behavior of both parent ion (CS2+) and fragment ions (S+ and CS+) was observed. It was found that all the ionic signals decay exponentially with lifetimes that were different for delay times, t>0 and t<0, which can be attributed to the evolution of different Rydberg states pumped by 267-nm and 400-nm laser pulses. The lifetimes of two Rydberg states were obtained simultaneously from one fitting of the transients. The fragment ions were produced by the dissociation of CS2+, and it is suggested that the final ionic state is the C2Σg+ state of CS2+ based on the measured S+/CS+ branching ratio. The S+/CS+ ratio is dependent on the delay time of the two lasers, indicating that the dissociation process of CS2+ is related to the evolution of the intermediate Rydberg state.展开更多
Ultrafast phenomena induced by femtosecond laser irradiation encompass a range of highly dynamic physical processes,including but not limited to electron excitation,material ablation,plasma generation,and shock wave p...Ultrafast phenomena induced by femtosecond laser irradiation encompass a range of highly dynamic physical processes,including but not limited to electron excitation,material ablation,plasma generation,and shock wave propagation.Unveiling the dynamics of these ultrafast processes is crucial for effectively controlling laser processing.However,many of these phenomena occur on timescales ranging from femtoseconds(fs) to nanoseconds(ns),which presents significant challenges in monitoring and interpretation;thus,ultrafast optical imaging techniques are often required.This paper comprehensively reviews the ultrafast optical imaging methods employed in recent years to monitor various ultrafast processes such as electron excitation,ultrafast ablation,plasma ejection,and shock wave propagation during femtosecond laser processing of metallic,composite,and ceramic materials.These methods can be categorized into two primary types:pump-probe ultrafast optical imaging and single-shot ultrafast optical imaging techniques.The working principles and key findings associated with each type of ultrafast optical imaging technique are described in detail.Finally,the imaging principles,advantages and disadvantages,and application scenarios of various ultrafast imaging technologies are summarized,along with a discussion of future challenges and development directions in this field.展开更多
The dicarbon(C_(2))molecule is an important molecular species observed in many carbon-containing gaseous environments.The spectroscopic and dissociative studies of C_(2)have attracted great attention for a long time f...The dicarbon(C_(2))molecule is an important molecular species observed in many carbon-containing gaseous environments.The spectroscopic and dissociative studies of C_(2)have attracted great attention for a long time for understanding its electronic characters as well as the evolution and cycling of carbon in the universe.In this study,the lifetimes of C_(2)populated at the three high-lying electronic states of(2-4)^(3)Δ_(g) in the vacuum ultraviolet(VUV)region have been experimentally measured using a time-of-flight mass spectrometer and the VUV-pump-UV-probe photoionization scheme.The measurements showed that all the rovibronic levels in the 2(g)^(3)Δ_(g) state exhibit shorter lifetimes than the dynamical limit of the experimental method,consistent with the theoretically predicted radiative lifetimes.Dependence of the lifetime on the vibrational level was observed in the 3^(3)Δ_(g) state,and a marginal rotational dependence was noticed in the vʹ=1 vibrational level.For the 4^(3)Δ_(g) state,the rotationally resolved lifetimes in the vʹ=1 vibrational level were found to be slightly longer than those in the vʹ=0 and 2 vibrational levels.Such a complicated dependence of the lifetime on the rovibronic level makes further experimental and theoretical investigations highly desired for understanding the dynamics in the high-lying excited states of C_(2).展开更多
Quantum materials have attracted a great deal of attention because of their rich landscape of electronic structures,topological phases,strong correlation effects,and exotic orders.These systems provide a fertile platf...Quantum materials have attracted a great deal of attention because of their rich landscape of electronic structures,topological phases,strong correlation effects,and exotic orders.These systems provide a fertile platform for the exploration of novel quantum phenomena and materials applications.Particularly exciting is the exploration of nonequilibrium dynamics in quantum materials,which has significant research and potential application values.Pump-probe techniques play a key role in revealing the dynamics of quantum materials on remarkably short timescales,providing an attractive yet challenging avenue of research.In this context,time-resolved x-ray as an emerging probe exhibits high time resolution,momentum resolution,and substantial momentum coverage.It can reveal unprecedented transient states,distinguish between entangled ordered states,and has a compelling potential to probe ultrafast dynamics in a wide variety of quantum materials.Despite its unique advantages,time-resolved x-ray scattering still faces several technological and methodological challenges.In this review,we highlight recent advances focusing on the use of time-resolved x-ray scattering to probe dynamic processes in quantum materials.We discuss representative examples across structural,electronic,magnetic,and lattice degrees of freedom,and outline promising directions for future research in this rapidly evolving field.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No 10534010)
文摘This paper reports that a one-colour fs pump probe measurement has been carried out for studying photoionization/photodissociation of cyclohexanone （C6H10O） in intense laser field. Two of the fragments from eyclohexanone, C2H＋ and C3H3＋, are studied under 800 nm laser pump-probe and the results obtained show similar time evolutions. It proposes a feasible model for analysing the experimental observations of the one-colour fs pump-probe measurement. The results demonstrate that as an intermediate product, the excited molecular parent ions play a very important role in photionization/photodissociation processes in intense laser field.
基金supported by the National Natural Science Foundation of China(No.21973102,No.21573243,and No.21327802)。
文摘In this work,we simulated 2D infrared spectroscopy(IR)spectroscopy in both transmission geometry and Brewster-angle reflection geometry.Light dispersion and the leakage of s-polarized light are considered in simulating the enhancement factor of the reflection mode.Our simulation shows that the dispersion in reflection will only alter the 2D IR lineshape slightly and can be corrected.Leaking spolarized light due to imperfectness of IR polarizers in the reflection geometry may limit the enhancement factor,but such limit is above what a typical experiment can reach.In the current experiment,the enhancement factor is mainly limited by the precision of incident angle,for which ordinary rotation stages are probably not adequate enough.Moreover,traditional energy ratio of pump and probe pulses,which is 9:1,may not be ideal and could be changed to 2:1 in the reflection geometry.Considering all the above factors,the enhancement on the order of 1000 is possible in the current experiment.Nevertheless,near-Brewster angle reflection will enhance both the signal and the noise caused by the signal itself,therefore this method only works if the noise is unrelated to the signal,particularly if the noise is caused by the fluctuation in the probe.It cannot improve the signal to noise ratio when the dominate noise is from the signal itself.The theoretical results here agree reasonably well with published experiment results and pave way for realizing even higher enhancement at nearer-Brewster angle.
基金The XFEL experiments were performed at the BL3 of SACLA with the approval of the Japan Synchrotron Radiation Research Institute(JASRI)(Proposals Nos.2014A8045,and 2014B8068)This research was partially supported by grants from Grants-in-Aid for Scientific Research(Kakenhi Grant Nos.15H02153 and 17K05729)+1 种基金the Core-to-Core Program on International Alliance for Material Science in Extreme States with High Power Laser of the Japan Society for the Promotion of Science(JSPS),from the X-ray Free Electron Laser Priority Strategy Program of the MEXT,contract 12005014,and within the state assignment of FASO of Russia(theme N01201357846)The part of work was supported by the Agence Nationale de la Recherche in the frame of the ANR project TurboHEDP(ANR-15-CE30-0011).
文摘We present new diagnostics for use in optical laser pump-X-ray Free Electron Laser(XFEL)probe experiments to monitor dimensions,intensity profile and focusability of the XFEL beam and to control initial quality and homogeneity of targets to be driven by optical laser pulse.By developing X-ray imaging,based on the use of an LiF crystal detector,we were able to measure the distribution of energy inside a hard X-ray beam with unprecedented high spatial resolution(~1 mm)and across a field of view larger than some millimetres.This diagnostic can be used in situ,provides a very high dynamic range,has an extremely limited cost,and is relatively easy to be implemented in pump-probe experiments.The proposed methods were successfully applied in pump-probe experiments at the SPring-8 Angstrom Compact free electron LAser(SACLA)XFEL facility and its potential was demonstrated for current and future High Energy Density Science experiments.
基金supported by the National Natural Science Foundation of China(11175094)the National Basic Research Program of China(2015CB921002)
文摘Opto-thermal relaxation is one of the most important properties of nonlinear optical materials.Rapid and high precision measurement of this parameter is vital in both fundamental research and applications.Current measurement uses either complicated structure with poor precision or high power heating source with low efficiency.Here,we propose a pump-probe method(PPM) to optically measure the thermal relaxation using whispering gallery mode(WGM) microcavities.When the pump laser shines on a microcavity,the materials absorb the input power resonantly and heat up.Then the heat dissipates from the cavities to the surroundings.The opto-thermal effect induces a refractive index change reflected in the signal light transmission spectra.By analyzing the curve character of the transmission spectra of the signal response in the spontaneous relaxation process,the thermal relaxation time can be rapidly measured with high precision.Additionally,we systematically verify the PPM using microtoroids under various pump powers and at various locking points of the signal laser mode.The small rate of refractive index changes($10à8) can be discerned with an input pump power as low as 11.816 l W.Hence,the PPM can be used to detect refractive index perturbation,like gas or liquid sensing,temperature fluctuations with ultra-high sensitivity and be applied to optical materials analysis efficiently.
基金supported by the Chinese National Key Basic Research Special Fund (2011CB922003)International Science and Technology Cooperation Program of China (2013DFA51430)+1 种基金NSFC—National Natural Science Foundation of China (11174159, 11374164, 11304166)the Fundamental Research Funds for the Central Universities (65145005)
文摘Pump-probe differential reflection and transmission spectroscopy is a very effective tool to study the nonequilibrium carrier dynamics of graphene. The reported sign of differential reflection from graphene is not explicitly explained and not consistent. Here, we study the differential reflection and transmission signals of graphene on a dielectric substrate. The results reveal the sign of differential reflection changes with the incident direction of the probe beam with respect to the substrate. The obtained theory can be applied to predict the differential signals of other two-dimensional materials placed on various dielectric substrates.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 10534010 and 20673140)
文摘The photodissociation/photoionization processes of chlorobromomethane (CH_2BrCl) induced by fem- tosecond laser pulses have been investigated using pump-probe scheme combined with the time-of-flight mass spectra. The dominate photoproducts are observed at different delay time of the pump (400 nm) and probe (800 nm) pulses and the corresponding time-dependence of them is obtained. The results show that the decaying time of the molecule CH_2BrCl in the A-band is in the 100 fs. The decaying tendencies of the fragment ions (CH_2Cl^+ and CH_2Br^+) and the parent ion (CH_2BrCl^+) are almost the same and the relative ratios of the yields of them keep constant during the delay time of 0 to 150 fs. These facts suggest that the fragment ions come from the fragmentation of the parent ions in excited electronic states. The probabilities to form CH_2Cl^+ and CH_2Br^+ are obtained from the relative ratio of the ion intensity and are about 71.6% and 14.2%, respectively.
基金supported by the National Natural Science Foundation of China (10874056 and 10534010)
文摘The ultrafast dynamics and dissociative ionization of CS2 were studied using the pump-probe method with time-of-flight mass spectroscopy. The transient behavior of both parent ion (CS2+) and fragment ions (S+ and CS+) was observed. It was found that all the ionic signals decay exponentially with lifetimes that were different for delay times, t>0 and t<0, which can be attributed to the evolution of different Rydberg states pumped by 267-nm and 400-nm laser pulses. The lifetimes of two Rydberg states were obtained simultaneously from one fitting of the transients. The fragment ions were produced by the dissociation of CS2+, and it is suggested that the final ionic state is the C2Σg+ state of CS2+ based on the measured S+/CS+ branching ratio. The S+/CS+ ratio is dependent on the delay time of the two lasers, indicating that the dissociation process of CS2+ is related to the evolution of the intermediate Rydberg state.
基金supported by the National Key R&D Program of China(No.2022YFB4601601)the Key R&D Program of Guangxi Province,China(No.GKAB23026101)+1 种基金the Base,Talent Special Project of the Guangxi Science and Technology Plan Project(No.Gui Ke AD23026149)Guangxi Natural Science Foundation,China(No.2023GXNSFBA026287)
文摘Ultrafast phenomena induced by femtosecond laser irradiation encompass a range of highly dynamic physical processes,including but not limited to electron excitation,material ablation,plasma generation,and shock wave propagation.Unveiling the dynamics of these ultrafast processes is crucial for effectively controlling laser processing.However,many of these phenomena occur on timescales ranging from femtoseconds(fs) to nanoseconds(ns),which presents significant challenges in monitoring and interpretation;thus,ultrafast optical imaging techniques are often required.This paper comprehensively reviews the ultrafast optical imaging methods employed in recent years to monitor various ultrafast processes such as electron excitation,ultrafast ablation,plasma ejection,and shock wave propagation during femtosecond laser processing of metallic,composite,and ceramic materials.These methods can be categorized into two primary types:pump-probe ultrafast optical imaging and single-shot ultrafast optical imaging techniques.The working principles and key findings associated with each type of ultrafast optical imaging technique are described in detail.Finally,the imaging principles,advantages and disadvantages,and application scenarios of various ultrafast imaging technologies are summarized,along with a discussion of future challenges and development directions in this field.
基金supported by the National Natural Science Foundation of China(No.22122308)Beijing National Laboratory for Molecular Sciences(BNLMS).Hong Gao is also partially supported by the Innovation Capability Support Program of Shaanxi Province(2023-CX-TD-49)supported by the China Postdoctoral Science Foundation(No.2020TQ0324).
文摘The dicarbon(C_(2))molecule is an important molecular species observed in many carbon-containing gaseous environments.The spectroscopic and dissociative studies of C_(2)have attracted great attention for a long time for understanding its electronic characters as well as the evolution and cycling of carbon in the universe.In this study,the lifetimes of C_(2)populated at the three high-lying electronic states of(2-4)^(3)Δ_(g) in the vacuum ultraviolet(VUV)region have been experimentally measured using a time-of-flight mass spectrometer and the VUV-pump-UV-probe photoionization scheme.The measurements showed that all the rovibronic levels in the 2(g)^(3)Δ_(g) state exhibit shorter lifetimes than the dynamical limit of the experimental method,consistent with the theoretically predicted radiative lifetimes.Dependence of the lifetime on the vibrational level was observed in the 3^(3)Δ_(g) state,and a marginal rotational dependence was noticed in the vʹ=1 vibrational level.For the 4^(3)Δ_(g) state,the rotationally resolved lifetimes in the vʹ=1 vibrational level were found to be slightly longer than those in the vʹ=0 and 2 vibrational levels.Such a complicated dependence of the lifetime on the rovibronic level makes further experimental and theoretical investigations highly desired for understanding the dynamics in the high-lying excited states of C_(2).
基金the National Key R&D Program of China(Grants Nos.2024YFA1408702 and 2021YFA1401903)Beijing Natural Science Foundation(Grant No.JQ24001)the National Natural Science Foundation of China(Grant No.12374143)。
文摘Quantum materials have attracted a great deal of attention because of their rich landscape of electronic structures,topological phases,strong correlation effects,and exotic orders.These systems provide a fertile platform for the exploration of novel quantum phenomena and materials applications.Particularly exciting is the exploration of nonequilibrium dynamics in quantum materials,which has significant research and potential application values.Pump-probe techniques play a key role in revealing the dynamics of quantum materials on remarkably short timescales,providing an attractive yet challenging avenue of research.In this context,time-resolved x-ray as an emerging probe exhibits high time resolution,momentum resolution,and substantial momentum coverage.It can reveal unprecedented transient states,distinguish between entangled ordered states,and has a compelling potential to probe ultrafast dynamics in a wide variety of quantum materials.Despite its unique advantages,time-resolved x-ray scattering still faces several technological and methodological challenges.In this review,we highlight recent advances focusing on the use of time-resolved x-ray scattering to probe dynamic processes in quantum materials.We discuss representative examples across structural,electronic,magnetic,and lattice degrees of freedom,and outline promising directions for future research in this rapidly evolving field.
