Optical Cross-correlation Technique Research Articles

From breather soliton molecules to chaos in a laser cavity: the scenario of intermittent transitions

Intermittency is widely observed in various nonlinear dynamical systems as an intriguing transient dynamic far from equilibrium. The internal dynamics formed by a pair of interacting optical solitons are often analogized to typical nonlinear systems. However, whether intermittency exists within the intramolecular motion remains to be investigated. Here, we study the intermittent dynamics of soliton molecules in ultrafast lasers, employing balanced optical cross-correlation techniques with sub-femtosecond temporal resolution. We demonstrate the occurrence of the bursting phase of intense variations of pulse separation within regular breather rhythms. In addition, we discover the intermittent transitions route to chaotic soliton molecules, facilitated by gain control. A series of analysis methods are used to assess the chaotic signals, providing compelling experimental evidence that soliton molecules can be analogized to their matter molecule counterparts. Our experimental findings shed light on the non-equilibrium intramolecular dynamics, providing insight into the transition of the attractors within interacting dissipative solitons in laser and fiber resonators.

Quasi-Period Dynamics of Soliton Molecules: Route to Chaos and Intrinsic Frequency Entrainment

Soliton molecules in optical resonators have attracted remarkable attention in nonlinear dynamics, driven by their compelling analogies with matter molecules. So far, while extensive research has been conducted on their generation, pulsations, and dissociation behaviors, the investigation of their quasi-periodic dynamics has been relatively limited. Here, we present a systematic exploration of the quasi-periodic dynamics of soliton molecules using advanced balanced optical cross-correlation techniques. The incommensurable quasi-period bifurcations constituted of cascaded Hopf bifurcations are found, providing an unambiguous pathway toward chaotic soliton molecules. The chaotic intramolecular dynamics are analyzed by time series, radio frequency spectra, phase portraits, and Lyapunov exponent analysis. In addition, we reveal an intrinsic frequency entrainment phenomenon experimentally. Such frequency entrainment provides a novel perspective on synchronization in optical resonators, encompassing the competition and interaction of oscillations across multiple temporal scales. Our experimental findings offer clear proof that the gain dynamics serve as the origin of the binding forces between solitons within the molecule, which are well supported by the numerical simulations. By advancing the understanding of sub-femtosecond resolved quasi-period dynamics of optical soliton molecules, this study contributes to the broader field of complex nonlinear dynamics, paving the way for future explorations into the intricate behaviors of solitons within optical resonators and relevant fields.

Optical up-conversion-based cross-correlation for characterization of sub-nanosecond terahertz-wave pulses.

Using a nonlinear optical mixing known as a frequency up-conversion process, we demonstrate an optical cross-correlation technique for the detection and characterization of sub-nanosecond (sub-ns) terahertz (THz)-wave pulses. A monochromatic THz-wave pulse from an injection-seeded THz-wave parametric generator (is-TPG) was mixed with a near-infrared (NIR) pump pulse to generate a NIR idler pulse in a trapezoidal-prism-shaped MgO-doped lithium niobate crystal under the noncollinear phase-matching condition. By measuring pump-energy and crystal-length dependencies, we show that the frequency up-conversion of sub-ns THz-wave pulses with and without subsequent parametric amplification can be used for sensitive detection and intensity cross-correlation characterization, respectively. Using this cross-correlation technique, we reveal that the temporal profile of THz-wave pulses from the is-TPG driven by a 351-ps 1064-nm pump laser has slightly-frequency-dependent pulse width in the range of 150-190 ps at full width at half-maximum in the tunable range of 0.95-2.00 THz.

Ultrafast amplifier additive timing jitter characterization and control.

We report on the characterization and long-term compensation of additive timing jitter introduced by a femtosecond ytterbium regenerative amplifier with a 100 kHz repetition rate. A balanced optical cross-correlation technique is used to generate a jitter error signal. This approach is well suited to characterize the additive timing jitter of Yb amplifiers seeded by narrow spectrum Yb oscillators. The balanced optical cross-correlator is in a noncollinear configuration allowing a background free coindence detection. This setup enables the measurement of additive timing jitter from the amplifier, with a noise floor of 300 as integrated from 10 Hz to 10 kHz. The measured additive timing jitter level is about 5 fs, integrated from 0.1 Hz to 10 kHz. The amplifier timing drift characterization and control are performed for more than an hour.

Timing jitter characterization of mode-locked lasers with

Timing jitter characterization of free-running mode-locked lasers with an unprecedented resolution is demonstrated using an optical heterodyne technique. A highly sensitive timing jitter phase-discrimination signal with low-parasitic-amplitude sensitivity is achieved. Analytical and numerical methods are used to analyze the properties of the discrimination signal. For an experimental demonstration, we measure the timing jitter between two loosely synchronized mode-locked Er:Yb:glass lasers with 500-MHz fundamental repetition rates. The timing jitter-detection noise floor for a single mode-locked laser reaches 2.8×10(-13) fs(2)/Hz (∼530 ys/√Hz), and the integrated timing jitter is 16.3 as from 10 kHz to the Nyquist frequency (250 MHz). These results show that this approach can be a simpler alternative to the well-established balanced optical cross-correlation technique.

Fast and Accurate Cell Tracking by a Novel Optical-Digital Hybrid Method

An innovative methodology to detect and track cells using microscope images enhanced by optical cross-correlation techniques is proposed in this paper. In order to increase the tracking sensibility, image pre-processing has been implemented as a morphological operator on the microscope image. Results show that the pre-processing process allows for additional frames of cell tracking, therefore increasing its robustness. The proposed methodology can be used in analyzing different problems such as mitosis, cell collisions, and cell overlapping, ultimately designed to identify and treat illnesses and malignancies.

Synchronization and Relative Timing Jitter Measurement of Femtosecond and Picosecond Laser Regenerative Amplifiers

In this paper, precise synchronization of the femtosecond and picosecond laser regenerative amplifiers with different wavelengths and independent seed oscillators was achieved using the electronic phase-locked loop and global clock techniques. The root-mean-square relative timing jitter of the two regenerative amplifiers was measured as 0.66 ps using a modified statistical method based on the error propagation relation between the independent variables and the conventional optical cross-correlation technique. The results suggest that this method is more accurate and requires simple optical setups for low-pulse repetition rate lasers.

Time-of-flight measurement with femtosecond light pulses

The time-of-flight of light pulses has long been used as a direct measure of distance1,2, but state-of-the-art measurement precision using conventional light pulses or microwaves peaks at only several hundreds of micrometres3,4. Here, we improve the time-of-flight precision to the nanometre regime by timing femtosecond pulses through phase-locking control of the pulse repetition rate using the optical cross-correlation technique5,6. Our experiment shows an Allan deviation of 117 nm in measuring a 0.7-km distance in air at a sampling rate of 5 ms once the pulse repetition is phase-locked, which reduces to 7 nm as the averaging time increases to 1 s. This enhanced capability is maintained at long range without periodic ambiguity, and is well suited to lidar applications such as geodetic surveying7, range finders8 and absolute altimeters9. This method could also be applied to future space missions involving formation-flying satellites for synthetic aperture imaging10,11 and remote experiments related to general relativity theory12. Scientists improve the precision of time-of-flight measurements from several hundreds of micrometres to the nanometre regime by timing femtosecond pulses through phase-locking control of the pulse repetition rate using the optical cross-correlation technique. This result looks set to benefit synthetic aperture imaging for future space missions of formation-flying satellites and remote experiments involving the general theory of relativity.

Study of a continuous plasma centrifuge

Results of experiments on a partially ionised argon plasma centrifuge are presented and interpreted. Centrifuge operation is quasi-continuous with a driving current pulse lasting for several seconds. An optical cross-correlation technique has been used to study plasma non-uniformities. Two distinct types of non-uniformity have been identified: (i) slow-moving contra-rotating spokes associated with cathode arc spots, and (ii) rapidly moving co-rotating striations. The striations lie at an angle of about 45 degrees to the electric field and are likely to be caused by the ionisation instability. From the observations it can be concluded that the heavy particles in the centrifuge are not rotating at the full Er/Bz velocity.