Dual-wavelength Laser Research Articles

A π-polarized 1084 nm laser with pump pulse modulation based on Nd:MgO:LiNbO3 crystal

A π-polarized （π-pol） 1084 nm laser based on Nd:MgO:LiNbO3 crystal under modulation pulsed pumping mode was demonstrated. The anisotropic Nd:MgO:LiNbO3 slab crystal was end-pumped by a pulsed laser diode (LD) with a different duty cycle for experiments. The dual-wavelength fundamental laser emission range was effectively controlled within a certain pump peak power interval, and the unmatched polarized fundamental laser is completely suppressed when the duty cycle is 20 % and below. At a repetition frequency of 5 Hz and pulse width of 40 ms, the π-pol 1084 nm fundamental laser with a maximum average output power of 1.396 W in the whole pump range was obtained, and the single pulse energy was 279.2 mJ.

Laser Impacts on Skin Rejuvenation: The Use of a Synergistic Emission of CO2 and 1540 nm Wavelengths.

Background and Objectives: For nearly 15 years, carbon dioxide (CO2) laser has been the gold standard in skin rejuvenation. Aim: The purpose of this study was to assess the efficacy of a new laser device which combines CO2 and 1540 nm wavelengths in wrinkles reduction, using a recently developed scanning unit named the µScan DOT scanner. Materials and Methods: A total of 20 female patients underwent from two to four laser treatment sessions performed once every 45-90 days. Wrinkles reduction was evaluated using the Fitzpatrick Wrinkle Classification System (FWCS). Evaluations of five-point Global Patient's Assessment (PGA) and an Oedema and Erythema index based on a four-point scale were carried out. A careful photographic evaluation was performed to observe the patients' aesthetic improvements. All the assessments were performed before and at 3 months follow up (3 MFU) after the last treatment session. Results: The mean FWCS score significantly (p < 0.01) decreased from 5.45 ± 2.21 at baseline to 3.3 ± 1.78 at 3 MFU after the last treatment session. In total, 8/20 (40%) subjects reported excellent improvement, 7/20 (35%) subjects showed good improvement, 5/20 (25%) subjects showed slight improvement, and 0/20 (0%) subjects showed no improvement. Concerning the Oedema index, 15/20 subjects experienced a mild one, 5/20 subjects experienced a moderate one, and none of 20 experienced a severe one, while for the Erythema index, 1/20 patients experienced mild, 18/20 patients experienced moderate, and only 1/20 patient experienced severe erythema. No severe adverse events were observed. Conclusions: This dual-wavelength laser technique may become a promising new option for safe, nonsurgical improvement for skin rejuvenation with an extremely low risk of scarring or hypopigmentation and shorter healing times.

Spectral dynamics of pseudo-distributed erbium gain in Raman random fiber laser

This work explores the spectral dynamics of pseudo-distributed erbium gain in a Raman-based open cavity hybrid random fiber laser (RFL) and compares it to two other schemes; without erbium-doped fiber (EDF) and with EDF integrated mid-cavity. The pseudo-distribution of erbium gain is simulated by splicing short segments of EDF in between single-mode fiber (SMF) spools. The three schemes have similar total SMF lengths of 78 km, and a total of 30 m EDF if any. It was established that the laser wavelength shifts significantly from 1555.936 nm to 1565.904 nm simply by the insertion of EDF mid-cavity, while the distribution of EDF segments along the cavity allowed the generation of dual-wavelength lasing at 1559.964 and 1565.236 nm. The distribution of EDF also generated a higher maximum output power of 485.60 mW compared to the schemes with lumped EDF and without EDF of 409.17 mW and 352.02 mW output powers, respectively. However, the increment came at the expense of a longer instability event from homogenous gain broadening of SBS induced Stokes and a delayed onset of laser threshold condition. We discuss the formations of these different laser schemes and its dynamics permitted solely due to the uniqueness of random fiber lasers. The scheme presents an interesting opportunity in the development of hybrid random fiber lasers, and the analysis of this structure offers insights for better designed dual-wavelength random fiber lasers and the role that rare-earth Erbium dopant plays in the formation of laser in a Raman-based fiber cavity.

Interval Adjustable Dual-Wavelength Erbium-Doped Fiber Laser Based on Cascaded Two Mach-Zehnder Interferometers

An interference filter is designed by cascading two Mach-Zehnder interferometers (MZIs), which is then utilized in the construction of a wavelength interval adjustable dual-wavelength Erbium-doped fiber laser (EDFL). Each MZI consists of two 3 dB optical couplers (OCs) connected in series. The input light is split into two arms at the first OC and recombined at the second OC. The first MZI (MZI 1) has a smaller free spectral range (FSR) and is used for selecting the output wavelength of the laser. The second MZI (MZI 2) has a larger FSR and forms an envelope structure on the comb-like spectrum of MZI 1. By adjusting the optical path difference between the two arms of MZI 2, the FSR of the envelope can be changed, thereby altering the interval of the output wavelengths. The implemented filter is inserted into the EDFL to achieve stable dual-wavelength output. By stretching one arm of MZI 2, the interval of the dual-wavelength can be adjusted from 4.64 to 13.94 nm, with the side-mode suppression ratio of over 44 dB for all wavelengths.

Red and green dual-wavelength Pr:LiGdF4 laser with a single birefringent filter

A simultaneous continuous-wave (CW) dual-wavelength Pr:LiGdF4 laser using a single birefringent filter (BF) plate under excitation with a frequency doubled optically pumped semiconductor laser (2 ω-OPSL) was experimentally demonstrated. We calculate the wavelength-dependent loss property of the BF. By adjusting the BF plate, the spectral intensity ratio of the generated wavelengths can be maintained to be 1:1. A simultaneous CW dual-wavelength Pr:LiGdF4 laser at 604 and 523 nm is experimentally realized. For a pump power of 7.2 W, red and green dual-wavelength laser radiation at 604 and 523 nm and 1.25 W of output power using a 4% output coupler could be generated. A slope efficiency of 19.8% with respect to the absorbed pump power and optical-to-optical efficiency of 17.4% for the highest-incident pump power were obtained. To our knowledge, this is the first study that has realized a dual-wavelength in Pr:LiGdF4 laser.

Active Differential Fiber Coupled Plasmon Waveguide Resonance Sensor Based on the Mode Competition Effect

We proposed an active differential intensity (DI) fiber coupled plasmon waveguide resonance (CPWR) sensor based on the mode competition effect in the C-band, aiming to enhance the sensitivity. The sensing head is a fiber probe with a sensing layer of ITO/Au/ITO/TiO2 film, enabling the excitation of CPWR in the C-band. The narrow CPWR spectrum allows DI interrogation by tracking the intensity of light at two wavelengths. The fiber probe is inserted into a dual-wavelength fiber laser to adjust the intra-cavity loss at the two lasing wavelengths. By using the differential modulation of the reflectivity from the refractive index variations, the mode competition effect is triggered. The powers at two lasing wavelengths change oppositely, enlarging the power difference and then resulting in enhanced sensitivity. The average sensitivity is up to 5702 dB/RIUs, which is 10 times higher than that of conventional DI interrogation. The sensitivity enhancement mechanism based on the mode competition effect provides a new technical approach for enhancing the sensitivity of DI SPR sensors.

Numerical Analysis of Dual-Wavelength Tungsten-Tellurite Fiber Raman Lasers with Controllable Mode Switching

Fiber laser sources in the spectral range near 1.7–1.8 μm are in highly demand for a lot of applications. We propose and theoretically investigate a dual-wavelength switchable Raman tungsten-tellurite fiber laser in the 1.7–1.8 µm range which can produce two stable modes at frequencies separated by ~7 THz with a pump at 1.55 µm. The Raman waves shifted by 19.8 THz (mode 1) and 27.5 THz (mode 2) from the pump frequency can be generated near two different maxima of the Raman gain spectrum (gain is higher at 19.8 THz and twice lower at 27.5 THz). We numerically simulate two-mode Raman lasing with allowance for energy transfer from the pump wave to modes 1 and 2, and from mode 1 to mode 2 due to inelastic Raman scattering. Diagrams of generation regimes depending on system parameters are constructed. We demonstrate controlled switching between two modes by changing the pump power. For the same intracavity losses for both Raman modes at relatively low pump powers, only mode 1 is generated. At medium pump power, generation occurs simultaneously in both modes. At relatively high pump power, only mode 2 is generated near the weaker maximum. This effect seems surprising, but a rigorous explanation with allowance for the nonlinear interaction between mode 1 and mode 2 is found. When losses for one of the modes change, switching of the generated regimes is also predicted.

Dual-wavelength femtosecond laser-induced single-shot damage and ablation of silicon

An experimental and theoretical study of laser-induced damage and ablation of silicon by two individual femtosecond pulses of different wavelengths, 1030 and 515 nm, is performed to address the physical mechanisms of dual-wavelength ablation and reveal possibilities for increasing the ablation efficiency. The produced craters and damaged areas are analyzed as a function of laser fluence and time separation between the pulses and are compared with monochromatic irradiation. The order of pulses is demonstrated to be essential in bi-color ablation with higher material removal rates when a shorter-wavelength pulse arrives first at the surface. Simulations based on the two-temperature model show that the visible pulse is profitable for the generation of the electron-hole plasma while the delayed IR pulse is efficiently absorbed in the plasma enhancing energy coupling to the target. At long delays of 30–100 ps, the dual-wavelength ablation is found to be particularly strong with formation of deep smooth craters. This is explained by the expansion of a hot liquid layer produced by the first pulse with a drastic decrease in the surface reflectivity at this timescale. The results provide insight into the processes of dual-wavelength laser ablation offering a better control of the energy deposition into material.

Control of dual-wavelength laser emission via optical feedback phase tuning

We propose and demonstrate a technique to control the balance between the two amplitudes of a dual-wavelength laser based on a phase-controlled optical feedback. The feedback cavity length is adjusted to achieve a relative phase shift between the desired emission wavelengths, introducing a boost in gain for one wavelength while the other wavelength experiences additional losses. Tuning the optical feedback phase proves to be an effective way to control the gain and losses, and, thus, to select one or balance the amplitude of the two emission wavelengths. This concept can be easily adapted to any platform, wavelength range and wavelength separations providing that a sufficient carrier coupling and gain can be obtained for each mode. To demonstrate the feasibility and to evaluate the performance of this approach, we have implemented two dual-wavelength lasers with different spectral separations together with individual optical feedback loops onto a InP generic foundry platform emitting around 1550 nm. An electro-optical-phase-modulator is used to tune the feedback phase. With this single control parameter, we successfully achieved extinction ratios of up to 38.6 dB for a 10 nm wavelength separation and up to 49 dB for a 1 nm wavelength separation.

Dual-Wavelength Q-switched Fiber Laser Generation by Incorporating 2D Materials in D-SMS Fiber Structure

We demonstrate a dual-wavelength Q-switched fiber laser generation by inserting a combination of SM-MM-SM fiber and a d-shape structure. This combination is known as D-SMS fiber. By side-polishing an SM fiber with 1-dB loss, the d-shape fiber structure is obtained. Then the d-shape SM fiber is spliced to 25 cm long MM and SM fiber to form a D-SMS fiber structure. After inserting D-SMS fiber, a stable dual-wavelength presence at 1562.8 nm and 1563.8 nm (1 nm wavelength spacing). The pulse train generates once we deposited a graphene oxide solution onto the surface of the d-shape structure. This Q-switching operation mode obtained from 45 mW to 111 mW pump power with a maximum pulse energy of 56 nJ. The repetition rate and pulse width have been recorded from 34 kHz to 55 kHz and from 10.22 µs to 6.47 µs, respectively.

Demonstration of a diode-pumped dual-wavelength metastable krypton laser

Demonstration of a diode-pumped dual-wavelength metastable krypton laser

Millimeter-wave generation based on a monolithic dual-wavelength DFB laser with four phase-shifted sampled gratings and equivalent chirp technology.

A dual-wavelength DFB laser array based on four phase-shifted grating and equivalent chirp technology is first proposed, fabricated, and experimentally demonstrated. The dual-wavelength emitting is achieved by symmetrically introducing two π phase shifts into a chirped four phase-shifted sampled grating cavity. Meanwhile, the beating signal of the dual-wavelength output is stabilized by applying an electro-absorption modulator integrated at the rear of the cavity. Under different grating chirp rates, a series of RF signals from 66.8 GHz to 73.6 GHz with a linewidth of less than 210 kHz is obtained.

Analysis of the Temperature Elevation of the Dual-Wavelength Diode Laser and the Er, Cr: YSGG Laser in Oral Soft Tissue Incisions.

Introduction: Lasers are one of the most advantageous tools that have been used in a variety of medical fields. Soft tissue management is an important part of oral and maxillofacial surgery. There are different surgical procedures for management; one of them is laser surgery. The purpose of this study was to compare the dual-wavelength diode laser and the Er, Cr: YSGG laser to choose the most effective laser for a soft tissue incision in oral and maxillofacial surgery regarding temperature elevation. Methods: A dual-wavelength diode laser (810 and 980 nm) with 1.5 W and 2.5 W power outputs and an Er, Cr: YSGG (2780 nm) with 2.5 W and 3.5 W power outputs were used to make 50 incisions in six freshly dissected sheep tongues. The temperature means were measured at initial, maximum temperatures, as well as the temperature rise (difference between initial and maximum), and all were compared between the groups of soft tissue. Results: The lowest mean temperature rise was observed with a 2.5 W Er, Cr: YSGG laser, and the highest mean temperature rise was observed with a 2.5 W diode laser, and all samples from the two lasers showed a statistically significant difference (P<0.05) in the temperature rise except the 1.5 W diode, which is higher but not statistically significantly different from the 3.5 W Er, Cr: YSGG laser (P=0.100). Conclusion: The power output of 2.5 W of an Er, Cr: YSGG laser produced low levels of temperature rise compared to a diode laser and produced surgical incisions with a lower probability of heat damage to surrounding tissues.

Nd:YSAG waveguide-grating vortex laser: design and implementation

In this work, we fabricate a hybrid waveguide-grating vortex laser in Nd:YSAG by using femtosecond laser direct writing (FsLDW). The detailed parameters of the hybrid structure are fixed by optical simulation. In experiments, an efficient vortex beam is produced in the passive operation at 1064 nm. Under optical pumping at 808 nm, a dual-wavelength waveguide laser at 1060/1062 nm as well as a waveguide-grating vortex laser at 1060 nm are obtained. The laser performance and diffraction properties of the generated vortex laser are detailed, studied, and discussed, providing meaningful reference results toward the practical applications of FsLDW and waveguide-grating structures in integrated photonics.

Tunable and switchable multi-wavelength pulsed fiber laser based on a nonlinear optical loop mirror and an improved Sagnac filter.

We propose and experimentally demonstrate a tunable and switchable multi-wavelength erbium-doped fiber ring pulsed laser based on a nonlinear optical loop mirror (NOLM) and an improved Sagnac filter. To achieve multi-wavelength pulsed laser output, we adopt a NOLM as a quasi-saturable absorber and an improved Sagnac loop as a wavelength selected filter. The constructed laser has a maximum output wavelength number of five with a pulse repetition frequency of 40.45kHz and pulse duration of 108ns. The laser can output single-wavelength and dual-wavelength pulsed lasers within a certain wavelength tuning range and a five-wavelength pulsed laser with a constant wavelength interval of 3nm by adjusting the polarization controller. Dual-wavelength, three-wavelength, and four-wavelength pulsed lasers with various wavelength intervals are also obtained. The output performance of the constructed laser is tested with a maximum average output power of 127.45µW and minimum pulse duration of 52ns, and the stability of the laser output is also tested with a maximum power fluctuation of 0.62dB and minimum wavelength drift of 0.51nm with pump power of 350mW.

Effective Separation of Raman Signals from Fluorescence Interference in Undyed and Dyed Textiles Using Shifted Excitation Raman Difference Spectroscopy (SERDS)

Textiles are an integral part of our everyday lives, e.g., in the form of clothing and furniture. Consequently, their analysis is of great interest in a wide range of application areas including quality control, textile recycling, forensics, and cultural heritage studies. Optical methods offer a large potential for rapid and nondestructive textile inspection. Raman spectroscopy is a particularly promising candidate for this task as it delivers a fingerprint of the sample on the molecular level, thus giving insights into the textile material composition. Currently, a major challenge preventing the widespread use of Raman spectroscopy for textile analysis is the strong fluorescence background originating from additives, e.g., dyes or the fiber material itself. To address this main limitation, this study applies shifted excitation Raman difference spectroscopy (SERDS) for the effective separation of Raman signals from interfering backgrounds. Using a customized Raman setup based on a dual-wavelength diode laser emitting at 785.2 and 784.6 nm, we present investigations for textile analysis and identification on a set of 22 dyed and undyed pure textiles and binary textile mixtures made of cotton, viscose, wool, polyester, and elastane. SERDS in combination with multivariate analysis is demonstrated as a powerful tool for a distinction between different fiber types and fibers of one material colored with various dyes. These results highlight the large potential of SERDS for textile material identification in selected application areas.

Phase-matching in terahertz quantum cascade laser sources based on Cherenkov difference-frequency mixing

Terahertz quantum cascade laser sources based on intra-cavity Cherenkov difference-frequency generation in dual-wavelength mid-infrared quantum cascade lasers are currently the only monolithic semiconductor laser technology that can deliver continuous-wave coherent terahertz output at room temperature. Because the Cherenkov difference-frequency generation process enables terahertz radiation generation and extraction across a wide range of frequencies, it is often assumed that phase-matching conditions for this process are automatically fulfilled. We theoretically analyze and experimentally demonstrate that phase-matching plays an important role in these devices, and significant improvements in terahertz power output can be achieved by adjusting the waveguide configuration of the quantum cascade lasers to provide better phase-matching.

Experimental and Theoretical Study of Dual-Wavelength Continuous-wave Laser in Yb:YAG at 1030 and 1048 nm

Experimental and Theoretical Study of Dual-Wavelength Continuous-wave Laser in Yb:YAG at 1030 and 1048 nm

Study on Dual-Wavelength Wide-Spectrum Erbium-Doped Fiber Ring Laser for Optical Fiber Interferometric Sensing System

In this paper, a novel dual-wavelength wide-spectrum erbium-doped fiber ring laser (EDFRL) for optical fiber sensing system is proposed and experimentally demonstrated. The output of EDFRL is theoretically simulated and classified depending on the theoretical analysis of laser threshold condition into “excited state” and “nonexcited state”. The influence of pump wavelength, fiber laser configuration, EDF length and output coupling ratio of EDFRL is discussed. The EDFRL pumped at 1480 nm wavelength and backward-pumped mode could achieve the stable maximum wide-spectrum output power. The output power fluctuation is lower than 0.06 dB and the center wavelengths shift is less than 0.01 nm. The practicability of EDFRL in a hybrid M-Z and Sagnac interferometer optical fiber sensing system is demonstrated through the comparison of SLD and EDFRL. Consequently, the EDFRL proposed in this study is expected to replace the traditional SLD in the optical fiber interferometric sensing system at a lower cost.

Investigation on transient process of dense hydrogen microdischarge by dual-wavelength laser interferometry

In this paper, the transient process of single-pulse hydrogen microdischarge with peak discharge current of at constant pressure of is investigated by dual-wavelength laser interferometry. It is found that the phase shift signals related to electrons and excited H (n = 2) atom appear almost simultaneously after breakdown, with a delay of 700 ns compared with the current signal. The velocity of the ionization wave is thus estimated to be on the order of . Subsequently, the current and phase signals increase rapidly, indicating that the energy deposited is applied to heat electron and gas, and strong molecular ionization and atomic excitation process occur in microdischarge. The phase signal for excited H (n = 2) atoms shows the maximum value at and then decreases rapidly, while the current reaches the peak at . In the duration between these two peaks the electronic degrees of freedom (DOF) continue to gain energy from the external field, but the energy transferred to the atomic DOF decreases. After , the current drops first rapidly, and then slowly decreases until the end of the discharge. In discharge attenuation process, the energy flowing into all DOF decreases. The phase-shift dispersion curve is obtained by changing laser frequency. Through the global optimized fitting of the phase shift curve, the average line-of-sight density of excited H (n = 2) atoms is estimated to be in microdischarge, and the corresponding broadening information is given.