Optical Injection Research Articles

Investigating the efficacy of Endolift laser and Nanofat as a combination therapy for horizontal neck lines compared to Nanofat autologous alone.

The emergence of horizontal neck wrinkles is increasingly becoming a focal point for both cosmetic professionals and clients. Various treatment approaches must be considered to address this issue effectively, owing to its diverse underlying causes. The study explores the potential of utilizing the Endolift laser in conjunction with nanofat injection as a viable treatment option. Twenty patients with horizontal neck wrinkles involved in the study. Ten patients underwent treatment with a combination of Endolift laser and nanofat injection and 10 patients treated with nanofat injection alone. The participants were monitored for 6 months post-treatment. Biometric measurements were utilized to assess outcomes, including changes in volume, depth, and area of the wrinkles, skin elasticity, as well as the diameter and density of the epidermis and dermis in the treated area. Skin improvement was evaluated by two independent dermatologists, who compared before and after photos in a blinded manner. Patient satisfaction levels were also documented. The Visioface analysis showed a notable decrease in neck wrinkle depth and area in both groups. However, the group receiving the combination treatment of Endolift laser and nanofat exhibited a significantly greater improvement compared to the group treated with nanofat alone. Skin ultrasonography results demonstrated an increase in thickness and density of the dermis and epidermis in both groups. Particularly, the group treated with Endolift laser-nanofat displayed significant enhancements in dermis and epidermis density and thickness when contrasted with the nanofat-only group. Analysis with Cutometer revealed a marked enhancement in skin elasticity in the Endolift-nanofat treated group in comparison to the nanofat-only treated group. Furthermore, in the Endolift-nanofat treated group, a substantial majority (90%) of patients exhibited improvement. Patient evaluations highlighted significant distinctions between the two groups, with 95% of patients in the Endolift-nanofat treated group demonstrating enhancement. Both methods notably enhance horizontal neck wrinkles; nevertheless, the combination of endolift laser and nanofat seems to be more efficient for treating horizontal neck wrinkles.

Micro-Fabrication of PMMA Using Electrochemical Discharges

The Poly (methyl methacrylate)-PMMA material also recognized as acrylic is an significant material for the different microsystem’s technologies. PMMA properties such as optical transparency, high hydrophilicity, biocompatibility, chemical inertness and lower autofluorescence, makes it a suitable candidate for the microfluidics devices These devices consist of the various micro-features i.e., micro-holes as well as the micro-channels. In current times, fabrication methods such as laser machining, hot embossing, injection molding, and mechanical cutting are predominantly used for the microfabrication in PMMA material. Nonetheless, the major processes such as laser machining and mechanical cutting exhibit some limitations due to issues like higher processing+setup costs, higher thermal damage, edge burr formations etc. Recently, a method i.e. machining with electrochemical discharges emerged as the potential alternative to the existing methods to machine the PMMA substrates. This method also called ‘electrochemical discharge machining (ECDM)’ considered to be the hybrid combination of microfabrication based on electric-discharge and electro-chemical processes. ECDM is a relatively simple, economical process which, in principle, can perform micro-fabrication in various materials irrespective of its electrical-conductivity, hardness as well as brittleness. In ECDM heat energy generated by electrochemical (EC) discharges in an electro-chemical cell (consists of a micro tool rod/electrode, a big-sized counter electrode and an aqueous alkaline electrolyte).In ECDM process, when voltage (>2 V) is provided between the smaller size tool (cathode) and bigger counter electrode (anode) which are kept in the aqueous KOH. The applied voltage results in the electrolysis of aqueous KOH electrolyte and produces gas bubbles of hydrogen (H2) at cathode point and of oxygen at anode point respectively. At the point of cathode (tool electrode) gas bubble production is very higher due to higher current density at the smaller tool surface. The subsequent increase in the applied voltage starts the process of merger of bubble which forms an envelope of gas film around the smaller tool electrode. At this stage, tool electrode gets complete isolation from surrounding electrolyte. Breakage of this gas film envelope happens at elevated voltage (> 24±0.1 V) and discharges are generated which produces heat energy. The material removal from the PMMA workpiece happens which is kept below the discharge producing tool. The material removal is result of melting, evaporation and etching due to heat energy.The most of research on ECDM is demonstrated for the glass and alumina ceramics in past decade which are electrically nonconductive workpieces. Nevertheless, the ECDM process has not been completely explored for the polymers, such as PMMA. Bhargav et al. have recently explored this process for the micro-channel formation in PMMA using NaOH electrolyte with 0.7 mm titanium tool electrode having cylindrical shapes. It is very much clear from the known literature that work related to PMMA micro-structuring using ECDM is scarce. Furthermore, the experimental analysis was directed on the micro-channel (> 700 µm) formation only. Consequently, there is a wide research gap for micro-structuring of PMMA for formation miniaturized micro-holes (> 300 µm) of different shapes such as circular, slotted. Analysing EC discharge behaviour, tool electrode condition, and micro-hole geometric features are the key tasks which are performed.The present work is performed to investigate the EC discharge behaviour and identification of the appropriate applied voltage on the micro-hole formation as well as the geometric characteristics such as hole size, depth, heat affected zone (HAZ) and circularity. Also, the tool condition after usage and its effect on the EC discharges and micro-hole quality have also been explored. The identification of Vc i.e. critical voltage has been carried out. The EC discharges stability for the range of applied voltage has been analyzed. It has been found that the applied voltage needed for the appropriate machining quality with uniform EC discharges should be in the range of Vc+4 to Vc+6. The lower values of applied voltage Vc+2 indicated the region of the unstable and non-uniform EC discharges affecting the micro-hole quality. The worn-out tool also affects the hole quality and EC discharge stability. Figure 1

(Invited) Colloidal Quantum Dot Laser Diodes: Three Decades in the Making

It has been 30 years since the first demonstration of lasing with semiconductor nanocrystals embedded in glass matrices1 – the samples akin to standard colored glass filters. Following this discovery, it took three years to realize lasing with epitaxial QDs2 and six more years to demonstrate the effect of amplified spontaneous emission (ASE) – a precursor of lasing – with colloidal QDs.3 So far, all reported studies into colloidal QD lasing have utilized optically excited samples. However, most of the prospective technological applications require electrically pumped devices, that is, laser diodes. The realization of such devices is complicated by multiple problems, widely deemed insurmountable. These include extremely fast nonradiative Auger recombination of optical-gain-active multicarrier states, poor stability of QD films under high current densities required for lasing, and unfavorable balance between optical gain and optical losses in electroluminescent (EL) devices wherein a gain-active QD medium is a small fraction of an overall device stack comprising multiple optically lossy charge-transport layers.Here we resolve these problems and achieve strong ASE with electrically driven QDs.4 To demonstrate this effect, we employ compact, continuously graded QDs with strongly suppressed Auger recombination incorporated into a low-loss photonic waveguide integrated into a pulsed light-emitting diode capable of operating at current densities of up to ~2000 A cm-2. These prototype ASE-type laser diodes exhibit strong, broad-band optical gain and demonstrate low-threshold, room-temperature ASE which leads to intense, edge-emitted EL whose instantaneous power reaches ~200 mW. 1. Vandyshev, Y. V., Dneprovskii, V. S., Klimov, V. I. & Okorokov, D. K. Lasing on a transition between quantum-well levels in a quantum dot. JETP Lett. 54, 442-445 (1991).2. Kistaedter, N., Ledentsov, N. N., Grundmann, M., Bimberg, D., Ustinov, V. M., Ruvimov, S. S., Maximov, M. V., Kopev, P. S., Alferov, Z. I. & Richter, U. Low threshold, large To injection laser emission from (InGa)As quantum dots. Electron. Lett. 30, 1416 (1994).3. Klimov, V. I., Mikhailovsky, A. A., Xu, S., Malko, A., Hollingsworth, J. A., Leatherdale, C. A., Eisler, H. J. & Bawendi, M. G. Optical gain and stimulated emission in nanocrystal quantum dots. Science 290, 314-317 (2000).4. Ahn, N., Livache, C., Pinchetti, V., Jung, H., Jin, H., Hahm, D., Park, Y.-S. & Klimov, V. I. Electrically driven amplified spontaneous emission from colloidal quantum dots. Nature 617, 79-85 (2023).

Comparing the Efficacy of Local Corticosteroid Injection and High-Intensity Laser Therapy in Patients with De Quervain Tenosynovitis

Background and Objective: De Quervain's tenosynovitis is one of the common causes of wrist pain. The present study aimed to compare the effectiveness of high-power laser therapy and local corticosteroid injection in the treatment of De Quervain's tenosynovitis. Materials and Methods: In this clinical trial, 30 patients diagnosed with De tenosynovitis were randomly assigned to two groups of 15, A and B. Group A underwent high-power laser therapy, five sessions for three consecutive weeks, and group B received corticosteroid injections of 1 ml triamcinolone and 1 ml lidocaine 2% in the wrist under ultrasound guidance. Tendon thickness, pain intensity, quality of life, and treatment satisfaction were measured and compared in both groups pre-treatment, month one, and month three post-treatment. Results: In groups A and B, respectively, the mean scores of the thickness of extensor abductor pollicis longus and abductor pollicis brevis muscles before the treatment were 7.57±0.63 and 7.25±0.58 (P=0.120). these value were calculated at 6.55±0.61 and 6.54±0.40 one month later (P=0.955). They were 5.71±0.75 and 5.99±0.45 (P=0.239) mm three months post-treatment. In addition, pain scores before the treatment were 8.60±1.18 and 8.47±1.46 (P=0.785). One month later, they were 2.73±1.66 and 4.27±1.16 (C=0.785), and three months post-treatment, they were 1.73±1.33 and 2.47±1.06 (P=0.007). There was no significant difference between the two groups in terms of quality of life and satisfaction with treatment (P<0.05 for all). Conclusion: Both local corticosteroid injection and high-power laser treatment methods were safe in the treatment of De Quervain's tenosynovitis, leading to a reduction in pain and tendon thickness, as well as an increase in the patient's quality of life

Customized machining of internal structure of droplet based on laser injection and templated self-assembly

Abstract The machining of micro- and nanostructures of droplets holds significant scientific and practical importance. A major challenge lies in customizing the internal architecture of droplets. In this work, we introduce a method that employs laser injection and templated self-assembly to precisely engineer the internal structures of droplets. Laser injection breaks the droplet’s inherent confinement, enabling the injection of any desired number of inner cores. The diverse topological defects of cholesteric liquid crystal droplets facilitate the templated self-assembly of these injected cores into ordered substructures, thus achieving the customization of the droplet’s internal structure. This study explores our capabilities in machining soft matter micro- and nanostructures within closed interfaces and promises potential applications in the development of functional materials, pharmaceuticals, and sensors.

Laser induced fluorescence using frequency modulated light.

The small signal-to-noise ratio (SNR) of conventional laser induced fluorescence (LIF) measurements using a continuous wave laser, either diode or dye, is typically overcome by amplitude modulating the laser at a specific frequency and then using lock-in amplification to extract the signal from measurement noise. Here, we present LIF measurements of the neutral helium velocity distribution function in an rf plasma using frequency modulated (FM) laser injection. A pulse train of 100% amplitude modulation is generated synthetically with a random sequence of pulse lengths. The FM signal then drives an acoustic optic modulator placed in the path of the injection beam in an LIF measurement. The signal from a fast photomultiplier tube is digitized and cross-correlated with the known modulation signal. The resultant FM-based LIF signal outperforms a conventional lock-in-based LIF measurement on the same plasma in terms of SNR and precision.

Properties of an optical event timer for satellite laser ranging

The resolution and above all the stability of the geodetic reference frames is crucially important when global change, such as the sea level rise is observed. In this context systematic errors are still presenting a significant challenge to the measurement techniques of space geodesy. In order to overcome this unfortunate situation for the satellite laser ranging technique, we have utilized the injection of a mode-locked laser to provide a stable low-noise link between the optical domain, where the measurements are carried out, and the microwave regime in which the station clock is defined. We obtained a considerably enhanced measurement delay stability by 10–20 ps over several days, albeit with some experimental challenges. The implementation of waveform scans required us to revisit the issue of target structure and intensity variation in satellite laser ranging.

Minimizing Noise in Distributed Reflector Laser Types Under Optical Injection Locking

Minimizing Noise in Distributed Reflector Laser Types Under Optical Injection Locking

Progress and challenges in the design of ITER's polarimetric Thomson scattering diagnostic system.

Polarimetric Thomson scattering (PTS) is a technique that allows for accurate measurements of electron temperature (Te) in very hot plasmas (Te > 10 keV, a condition expected to be regularly achieved in ITER). Under such conditions, the spectral region spanned by the TS spectrum is large and extends to low wavelengths, where the transmission of the collection optics decreases, available detectors are less efficient, and the high level of plasma background light perturbs the measurements. This work presents the recent developments in the design of a PTS system for ITER, along with the challenges posed by the complex machine design. The system performance is assessed for an updated geometry (with respect to previous publication), showing that, with a scattering angle θscat = 167°, the expected signal is strongly reduced. Potential alternatives are analyzed: (1) a system employing a different laser injection position, allowing for a more favorable scattering angle and (2) a recently proposed dual-polarization laser pulse technique. The latter is evaluated for the possible ITER geometry, again showing that a more favorable scattering angle is needed for a robust performance.

Improving pulsed laser induced fluorescence distribution function analysis through matched filter signal processing.

Laser induced fluorescence is used to measure argon ion heating during magnetic reconnection in the PHase Space MApping experiment (PHASMA). Sufficient signal-to-noise ratio (SNR) of the processed signal with pulsed laser injection is a delicate balance between saturation of the absorption line and injecting enough laser power to overcome the spontaneous emission of the plasma at the fluorescence wavelength. Averaging over many laser pulses and integrating over the fluorescence lifetime improves the SNR of the processed signal (processed SNR) when the SNR of the laser pulse time series is small (pulse SNR), but for laser powers small enough to avoid saturation, averaging over hundreds of pulses is needed to obtain an appreciable processed SNR over the entire Doppler-broadened absorption line. Here, we describe a matched filter processing method that significantly improves the SNR of the final measurement with fewer shots averaged. Investigation of simulated measurements validated by experimental results suggests that the matched filter method provides up to a 20% improvement in the processed SNR, resulting in less uncertainty in distribution function fits.

Design optimization of a modified Uni-Traveling- carrier photodiode for high optical power operation

We systematically investigated the design optimization of an InGaAs/InP modified Uni-Traveling-Carrier Photodiode (MUTC-PD) under high optical power input conditions. Based on internally fabricated experimental devices for a baseline design, we first achieved an excellent match between our experimental and simulation results under low optical power density of 1.4 mW/μm2, demonstrating the accuracy of our simulation model. Based on this model we showed that as optical power injection increases, the intrinsic bandwidth of the MUTC-PD degradation is the primary limitation on its high-speed response. We quantitatively analyzed the fundamental carrier transport physics and key design parameters affecting intrinsic bandwidth degradation under these conditions. In particular cliff layer doping concentration was found to be a very sensitive parameter affecting the MUTC-PD Optical Electrical (OE) intrinsic bandwidth. Based on detailed simulated results, we realized an optimized device design that is capable of achieving a 3 dB bandwidth of approximately 230 GHz at 10 mW/μm2 input optical power density for the first time.

Exploration of a brain-inspired photon reservoir computing network based on quantum-dot spin-VCSELs

Based on small-world network theory, we have developed a brain-inspired photonic reservoir computing (RC) network system utilizing quantum dot spin-vertical-cavity surface-emitting lasers (QD spin-VCSELs) and formulated a comprehensive theoretical model for it. This innovative network system comprises input layers, a reservoir network layer, and output layers. The reservoir network layer features four distinct reservoir modules that are asymmetrically coupled. Each module is represented by a QD spin-VCSEL, characterized by optical feedback and optical injection. Within these modules, four chaotic polarization components, emitted from both the ground and excited states of the QD Spin-VCSEL, form four distinct reservoirs through a process of asymmetric coupling. Moreover, these components, when emitted by the ground and excited states of a driving QD spin-VCSEL within a specific parameter space, act as targets for prediction. Delving further, we investigated the correlation between various system parameters, such as the sampling period, the interval between virtual nodes, the strengths of optical injection and feedback, frequency detuning, and the predictive accuracy of each module’s four photonic RCs concerning the four designated predictive targets. We also examined how these parameters influence the memory storage capabilities of the four photonics RCs within each module. Our findings indicate that when a module receives coupling injections from more than two other modules, and an RC within this module is also subject to coupling injections from over two other RCs, the system displays reduced predictive errors and enhanced memory storage capacities when the system parameters are fixed. Namely, the superior performance of the reservoir module in predictive accuracy and memory capacities follows from its complex interaction with multiple light injections and coupling injections, with its three various PCs benefiting from three, two, and one coupling injections respectively. Conversely, variations in optical injection and feedback strength, as well as frequency detuning, introduce only marginal fluctuations in the predictive errors across the four photonics RCs within each module and exert minimal impact on the memory storage capacity of individual photonics RCs within the modules. Our investigated results contribute to the development of photonic reservoir computing towards fast response biological neural networks.

Nonlinear Dynamics of Silicon-Based Epitaxial Quantum Dot Lasers under Optical Injection

For silicon-based epitaxial quantum dot lasers (QDLs), the mismatches of the lattice constants and the thermal expansion coefficients lead to the generation of threaded dislocations (TDs), which act as the non-radiative recombination centers through the Shockley–Read–Hall (SRH) recombination. Based on a three-level model including the SRH recombination, the nonlinear properties of the silicon-based epitaxial QDLs under optical injection have been investigated theoretically. The simulated results show that, through adjusting the injection parameters including injection strength and frequency detuning, the silicon-based epitaxial QDLs can display rich nonlinear dynamical states such as period one (P1), period two (P2), multi-period (MP), chaos (C), and injection locking (IL). Relatively speaking, for a negative frequency detuning, the evolution of the dynamical state with the injection strength is more abundant, and an evolution path P1-P2-MP-C-MP-IL has been observed. Via mapping the dynamical state in the parameter space of injection strength and frequency detuning under different SRH recombination lifetime, the effects of SRH recombination lifetime on the nonlinear dynamical state of silicon-based epitaxial QDLs have been analyzed.

Broadband stepped-frequency radar waveform generation by Fourier domain mode-locking period-one laser dynamics.

A stepped-frequency (SF) radar waveform generation method based on Fourier domain mode-locking (FDML) period-one laser dynamics is proposed and demonstrated. By fast controlling the optical injection strength of a semiconductor laser through electro-optical modulation, a broadband SF signal is generated. By further introducing an optoelectronic feedback loop with its round trip time delay matched with the temporal period of the SF signal, FDML is enabled through which the frequency stability, accuracy, and in-band signal-to-noise ratio are greatly improved. In the experiment, SF signals with a bandwidth of 6 GHz (12-18 GHz) and a frequency step of 150 MHz are generated. By comparing the qualities of signals generated with and without FDML, advantages of the proposed SF signal generation method are verified. Based on the proposed SF signal generation method, high-resolution inverse synthetic aperture radar (ISAR) imaging is also demonstrated, in which the 2D imaging resolution reaches 2.6 cm × 3.82 cm.

High-precision passive stabilization of a dissipative soliton resonance laser repetition rate based on optical pulse injection.

I present what is believed to be the first demonstration of using the cross-phase modulation (XPM) effect to achieve high-precision, all-optical synchronization and stabilization of the pulse repetition rate of a dissipative soliton resonance (DSR) mode-locked (ML) fiber laser working in the 1.06 µm wavelength range. Nanosecond 1.55 µm Master oscillator pulses were injected into the Slave cavity of the DSR laser to induce the XPM effect and subsequently synchronize both repetition rates. When referencing the Master laser to a rubidium frequency standard, the fractional instability of the DSR ML laser pulse repetition rate reached 1.26 × 10-12 for 1000 s integration time. The locking range and stability of the XPM synchronization are experimentally verified under varying conditions and discussed in the paper.

Combined CO2 Laser Vaporization and Bleomycin Injection to Treat Huge Adult Laryngeal Vascular Anomalies: Innovative Application of CO2 Laser in Otolaryngology.

The aim of this study was to assess the value of CO2 laser vaporization in treating huge adult laryngeal vascular anomalies (HALVAs) by combining it with bleomycin injection. This study retrospectively reviewed the records of 13 adult patients who underwent 18 different procedures. Methods to treatHALVAs include traditional bleomycin injectionand CO2 laser vaporization combined with bleomycin injection between September 2009 andJanuary 2023. Treatment results were evaluatedby the grade of lumen constriction. A total of five males and eight females, with an average age of 46.3 years (range, 22-66 years), were included in the study. The huge adult laryngeal vascular anomalies in our study were greater than 1633.71 mm3, and the long diameters of the bases were longer than 15 mm. Compared with the bleomycin injection-only group, the results with the CO2 laser vaporization and bleomycin injection combined were better. Both bleomycin injection and CO2 laser vaporization are safe treatment methods. Their combination may produce better results for huge adult laryngeal vascular anomalies.

Clinical efficacy of CO2 fractional laser combined with compound betamethasone in treating vitiligo and its impact on inflammatory factors.

To analyze the clinical efficacy of CO2 fractional laser combined with compound betamethasone in treating vitiligo and its impact on inflammatory factors. The clinical treatment effects, levels of inflammatory factors [interleukin-17 (IL-17), interferon-gamma (IFN-γ), interleukin-10 (IL-10)], prognosis regarding repigmentation and relapse, psychological health (satisfaction). ① Clinical treatment effects: the total effective rate in Group A was 92.73%, Group B was 74.55%, and Group C was 67.27%, with Group A showing significantly higher effectiveness than Groups B and C (p < 0.05). ② Inflammatory factors: prior to treatment, there was no significant difference in IL-17, IFN-γ, and IL-10 levels among the three groups (p > 0.05); after 3 and 6 months of treatment, the levels of IL-17 and IFN-γ decreased significantly while IL-10 levels increased significantly across all three groups, with Group A showing a more pronounced change compared to Groups B and C (p < 0.05). ③ Prognosis regarding repigmentation and relapse: after 3 and 6 months of treatment, Group A exhibited significantly higher repigmentation rates compared to Groups B and C (p < 0.05); in terms of relapse, Group A had a relapse rate of 5.45%, Group B had 21.82%, and Group C had 23.64%, with Group A showing significantly lower relapse rates compared to Groups B and C (p < 0.05). ④ Quality of life and psychological health: at the end of the 6 month follow-up, the quality of life and psychological health of patients in Group A were significantly higher than those in Groups B and C (p < 0.05). ⑤ Occurrence of adverse reactions: the incidence of adverse reactions was 12.73% in Group A, 10.91% in Group B, and 9.09% in Group C, with no significant difference observed among the three groups (p > 0.05). The application of CO2 fractional laser combined with compound betamethasone in vitiligo patients demonstrates significant efficacy. Compared to sole treatment with CO2 fractional laser or compound betamethasone injections, this combined approach further improves the levels of inflammatory factors in vitiligo patients, reduces the risk of relapse, enhances skin repigmentation, improves quality of life, psychological well-being, without increasing the risk of related adverse reactions. This combined approach merits clinical promotion and application.

Optical spin injection and detection in submonolayer InAs/GaAs nanostructures by circularly polarized photoluminescence

Optical spin injection and detection in submonolayer InAs/GaAs nanostructures by circularly polarized photoluminescence

Directed energy deposition with a graded multi-material compatibility interface enables deposition of W on Cu

Multi-material Directed Energy Deposition of new high-performance components is limited by phase incompatibilities between metals and by the composition variations which complicate parameter optimization. In this work, a methodology of incorporation of a graded Multi-Material Compatibility Interface (MMCI) was employed to allow deposition of tungsten layers (melting at 3410 °C) on a much less refractory metal, copper (boiling at 2562 °C). The manufacturing of parts combining tungsten and copper is of interest for components designed to dissipate heat in extreme environments, such as the divertor for tokamak fusion reactors. A succession of miscible filler metals rationally selected from thermodynamics were printed by laser and powder injection, with optimization of energy and material inputs for each layer, supported by material characterization and physical numerical analysis of the process phenomenology. 90 %wt. tungsten layer deposition on a copper initial substrate is achieved using an MMCI with 6 intermediate layers and 1.6 mm total thickness. The results reveal the importance of controlling the dilution ratio to achieve stable depositions of multi-material with compositional gradients, with a progressive increase in melt pool temperatures. The numerical analysis highlighted the important role of the dissolution and mixing of partially melted refractory powders, and the selective vaporization of volatile elements.

Nonlinear dynamics of a laser diode subjected to both optical injection and optical feedback

We analyse theoretically the nonlinear dynamics of a single-mode laser diode subjected to both optical injection and optical feedback. Detailed mappings of the laser dynamics reveal that, due to optical feedback (OF), the locking boundaries resulting from optical injection (OI) shift towards larger negative detunings and higher injection rates and display a periodic pattern of the injection locking boundaries. We demonstrate how feedback induces a cascade of quasiperiodic bifurcations associated with abrupt dynamic changes, hence altering the route to locking. A close inspection of the laser optical spectra for increasing feedback rate reveals the complex interplay between undamped relaxation oscillations and external cavity frequencies.