Dual-wavelength Continuous-wave Research Articles

High-power single-frequency continuous-wave 355 nm UV laser via a frequency-correlated dual-wavelength laser.

An all-solid-state single-frequency continuous-wave (CW) 355 nm ultraviolet (UV) laser based on a dispersion-compensated doubly resonant resonator is presented in this Letter that is achieved by employing homemade high-stability all-solid-state frequency-correlated dual-wavelength lasers at 1064 and 532 nm and a temperature-controlled type-I critical-phase-matching LiB3O5 (LBO) to act as the fundamental laser source and the nonlinear medium, respectively. The frequency-correlated dual-wavelength single-frequency CW laser supplies the fundamental frequency 1064 and 532 nm lasers with good frequency synchronization. And the temperature-controlled LBO acts as the dispersion-compensation element to realize double resonance of the 1064 and 532 nm laser. Finally, a 4.2 W high-stability 355 nm UV laser is experimentally obtained, and the corresponding total conversion efficiency is up to 20.5%. To the best of our knowledge, this is the highest power reported about single-frequency CW 355 nm UV laser. The presented method can pave a way to develop a compact single-frequency 355 nm UV laser with high output power.

Dual-Wavelength Continuous-Wave and Passively Q-Switched Alexandrite Laser at 736.7 nm and 752.8 nm

A dual-wavelength continuous-wave (CW) and passively Q-switched alexandrite laser based on a MoS2 saturable absorber (SA) operating at 736.7 nm and 752.8 nm with a simple and compact 18 mm plano–plano resonator is reported. In the CW mode, the output power is 1014 mW at the linear-polarized pump power of 5.44 W, with a slope efficiency of 28.7%. In the pulsed operation, the narrowest pulse width and the maximal peak power are 154 ns and 10.6 W, respectively. This laser can be used to generate 8.71 THz-wave light based on a suitable nonlinear optical crystal.

Dual-Wavelength Continuous Wave Photoacoustic Doppler Flow Measurement

Photoacoustic Doppler flow measurement based on continuous wave laser excitation owns the merit of clearly presenting the Doppler power spectra. Extending this technique to dual wavelengths can gain the spectral information of the flow sample extra to the flow speed information. An experimental system with two laser diodes respectively operated at 405 nm and 660 nm wavelengths is built and the flow measurement with black and red dyed polystyrene beads is performed. The measured Doppler power spectra can vividly reflect the flow speed, the flow direction, as well as the bead color. Since it is straightforward to further apply the same principle to multiple wavelengths, we can expect this type of spectroscopic photoacoustic Doppler flow measurement will be developed in the near future which will be very useful for studying the metabolism of the slowly moving red blood cell inside microvessels.

Switchable generation of multi-wavelength continuous wave and square-wave pluses in a bidirectional Erbium-doped fiber laser

We present a switchable generation of multi-wavelength continuous wave (CW) and square-wave pluses (SWPs) in a bidirectional erbium-doped fiber laser. The variable attenuator (VA) is used to realize switchable generation of CW and mode-locking pulse. In the multi-wavelength loop (MWL), the laser using the Sagnac loop output single-wavelength, dual-wavelength and triple-wavelength CW by finely adjusting the polarization controllers (PC). In the mode-locked loop (MML), the stable SWPs and harmonic mode-lock (HML) SWPs can be obtained by nonlinear polarization rotation (NPR) technique.

Dual-Wavelength Diffuse Optical Tomographic System for Direct Concentration Measurement

This article presents a promising dual-wavelength continuous wave (CW) diffuse optical tomography (DOT) system for direct estimation of concentrations and hemodynamic parameters for potential application in detection of rheumatoid arthritis (RA). The generalized curved-beam reconstruction technique is modified for direct estimation of hemodynamic parameters. The Rosenbrock’s function is fit to estimate the photon path as curved one followed by majority photons that enabled the use of modified Beer–Lambert law (MBLL) in differential form with assumption that unknown absorption coefficient ( $\mu _{a}$ ) varies from one path to another. The $\mu _{a}$ values are calculated and back-projected along the photon paths for image reconstruction without solving the inverse problem. Thus, stability is not an issue in image reconstruction. Also, there is no need for baseline measurement and prior information on perturbation, unlike the iterative methods used for dynamic imaging. The reconstructed images of the distal interphalangeal (DIP) and proximal interphalangeal (PIP) joints of a healthy male volunteer showed good consistency and are used for direct optical estimation of the physiological parameters. A novel application of optical imaging beyond biomedical applications is demonstrated by imaging the gradual dispersion of viscous Indian ink and glycerin mixture in turbid water with encouraging results.

Passively Q-Switched Mode-Locking Nd:(Gd0.3Y0.7)2SiO5 Laser Based on Semiconductor Saturable Absorber Mirror†

A diode-end-pumped continuous-wave and passively Q-switched mode-locked Nd:(Gd0.3Y0.7)2SiO5 laser was designed. At a pump power of 0.8W, we achieve dual-wavelength continuous-wave (CW) laser generation at wavelengths around 1,073.26 and 1,076.62 nm. Using a semiconductor saturable absorber mirror (SESAM), we obtain passively Q-switched mode-locked (QML) operation. A maximum average output power of 171 mW is obtained under a pump power of 5 W. The optical conversion efficiency for the QML laser is 3.4%. The duration of the mode-locked pulse is estimated to be about 649 ps at a repetition rate of 101.34 MHz.

Highly efficient dual-wavelength mid-infrared CW Laser in diode end-pumped Er:SrF2 single crystals.

The spectral properties and laser performance of Er:SrF2 single crystals were investigated and compared with Er:CaF2. Er:SrF2 crystals have larger absorption cross-sections at the pumping wavelength, larger mid-infrared stimulated emission cross-sections and much longer fluorescence lifetimes of the upper laser level (Er3+:4I11/2 level) than those of Er:CaF2 crystals. Dual-wavelength continuous-wave (CW) lasers around 2.8 μm were demonstrated in both 4at.% and 10at.% Er:SrF2 single crystals under 972 nm laser diode (LD) end pumping. The laser wavelengths are 2789.3 nm and 2791.8 nm in the former, and 2786.4 nm and 2790.7 nm in the latter, respectively. The best laser performance has been demonstrated in lightly doped 4at.% Er:SrF2 with a low threshold of 0.100 W, a high slope efficiency of 22.0%, an maximum output power of 0.483 W.

Labeling cellular structures in vivo using confined primed conversion of photoconvertible fluorescent proteins.

The application of green-to-red photoconvertible fluorescent proteins (PCFPs) for in vivo studies in complex 3D tissue structures has remained limited because traditional near-UV photoconversion is not confined in the axial dimension, and photomodulation using axially confined, pulsed near-IR (NIR) lasers has proven inefficient. Confined primed conversion is a dual-wavelength continuous-wave (CW) illumination method that is capable of axially confined green-to-red photoconversion. Here we present a protocol to implement this technique with a commercial confocal laser-scanning microscope (CLSM); evaluate its performance on an in vitro setup; and apply primed conversion for in vivo labeling of single cells in developing zebrafish and mouse preimplantation embryos expressing the green-to-red photoconvertible protein Dendra2. The implementation requires a basic understanding of laser-scanning microscopy, and it can be performed within a single day once the required filter cube is manufactured.

Dual-wavelength CW a-cut Nd:YVO4 laser at 1064.3 and 1066.7 nm

We demonstrate a dual-wavelength continuous-wave (CW) Nd:YVO4 laser working at 1064.3 and 1066.7nm. At a pump power of 7.25W, the maximum total output power is 1140mW and the optical conversion efficiency is 15.7%. The spectral line-widths of the dual-wavelength line are 1.1nm and 1.2nm, respectively. This laser system is very simple, compact and efficient.

Nd:(Gd0.3Y0.7)2SiO5 crystal: A novel efficient dual-wavelength continuous-wave medium

Efficient dual-wavelength continuous-wave (CW) and passively Q-switched laser operation of Nd:(Gd0.3Y0.7)2SiO5 crystal were investigated for the first time to our knowledge. Maximum CW output power of 2.3W was obtained under the absorbed pump power of 4.6W, corresponding to the slope efficiency of 55%. Dual-wavelength CW laser with respective wavelengths around 1074nm and 1078nm were achieved. With Cr4+:YAG as the saturable absorber, passive Q-switched performance was obtained. The slope efficiency of passively Q-switched operation was 45%. The shortest pulse width, the corresponding pulse energy and peak power were calculated to be 13.1ns, 50.2μJ and 3.8kW, respectively.

The research of laser crystal length impact on the self-Raman dual-wave length lasers output characteristics

Abstract In this work, the loss item of fundamental photon number which caused by the Raman effect is introduced into the rate equation of the fundamental laser, basing on this, the couple equations of self-Raman dual-wavelength continuous wave lasers is constructed. Through the solution of these equations, we achieved the expressions of output power of fundamental and Raman laser respectively and numerically simulated the output characteristics under the condition of different crystal length, including the separate output power, total output power and the ratio of two different wave lengths and deeply analyzed the physical mechanism under different output characteristics. The results show that crystal length of fundamental and Raman lasers are directly relevant to the characteristics of output, in which the former has minimally effect and the latter has maximally effect on it.

CW and passively Q-switched laser performance of Nd:Lu2SiO5 crystal

We demonstrated an efficient and controllable dual-wavelength continuous-wave (CW) laser of Nd:Lu2SiO5 (Nd:LSO) crystal. The maximum output power was 3.02W at wavelength of 1075nm and 1079nm, and with increasing of absorbed pump power, the ratio of 1079nm laser rose. The slope efficiency of 65.6% and optical-to-optical conversion efficiency of 63.3% were obtained. The passively Q-switched laser properties of Nd:LSO were investigated for the first time. The shortest pulse, maximum pulse energy and peak power were 11.58ns, 29.05μJ and 2.34kW, respectively.

Tunable, dual-wavelength interferometrically coupled continuous-wave parametric source

Generation of dual-wavelength continuous-wave (cw) radiation with independent and arbitrarily tuning, and indefinitely close spacing, using two cw optical parametric oscillators (OPOs) coupled with an anti-resonant ring interferometer is reported. The singly resonant OPOs, based on identical 30-mm-long MgO:sPPLT crystals, are pumped by a single cw laser at 532 nm. Two pairs of signal and idler wavelengths can be independently and arbitrarily tuned, with each signal (idler) pair tuned through degeneracy and beyond. Frequency separation between two distinct resonant signal waves from 7 down to 0.8 THz is demonstrated, and their overlap at 951 nm providing a frequency difference as small as ~220 MHz is shown. The OPOs independently provide a signal (idler) wavelength coverage across 870–1,000 nm (1,040–1,370 nm) and simultaneously generate idler powers of >1 W.

Dual-wavelength CW diode-end-pumped a-cut Nd:YVO4 laser at 1064.5 and 1085.5 nm

A simple and compact dual-wavelength continuous wave (CW) laser-diode end-pumped laser operating simultaneously at 1,064.5 and 1,085.5 nm in a single a-cut Nd:YVO4 has been demonstrated. We have used two Nd:YVO4 crystals with different Nd+3 concentrations and lengths; 0.1 %-14 mm and 0.25 %-12 mm. The maximum total output power of 5 and 6.18 W, including 1,064.5 and 1,085.5 nm, is achieved at the incident pump power of 22 and 18 W, with a slope efficiency 23.3 and 32.9 %, respectively, for the crystals of 0.1 %-14 mm and 0.25 %-12 mm. The calculations show both wavelengths lasing at 1,064.5 and 1,085.5 nm can possess the same threshold when reflectivity of the output coupler at 1,064.5 nm is less than 87.5 % and, at this condition, the reflectivity of the output coupler at 1,085.5 nm increases nearly linearly with that of 1,064.5 nm.

A quasi-three-level dual-wavelength thin-disk laser at 1024 and 1030 nm based on a diode-pumped Yb:YAG crystal

A diode-end-pumped Yb:YAG dual-wavelength continuous-wave (cw) laser that generates simultaneous laser action at wavelengths of 1024 and 1030 nm is demonstrated for the first time. A total output power of 897 mW for the dual-wavelength was achieved at an incident pump power of 17.8 W. Furthermore, intracavity sum-frequency mixing at 1024 and 1030 nm was then realized in an LBO crystal to reach the green range. We obtained a total cw output power of 85 mW at 513.5 nm.

Dual wavelength continuous wave laser using a birefringent filter

We report simultaneous dual wavelength continuous laser emission with minimum cavity elements. Tunable dual wavelength emission between 805 nm and 840 nm was observed with controlled peak separation around two nanometers, which corresponds to approximately one terahertz. Dual wavelength laser operation is possible using a novel intracavity two plate birefringent filtering element.

Evolution of dual-wavelength fiber laser from continuous wave to soliton pulses

Evolution of dual-wavelength fiber laser from continuous wave to soliton pulses is investigated experimentally by using the nonlinear polarization rotation technique. With the increase of pump power, the proposed laser successively delivers the dual-wavelength continuous wave, the single-wavelength soliton pulses, and the dual-wavelength soliton pulses. The dual-wavelength laser operates at the central wavelengths of about 1533 and 1546nm with the separation of ∼13nm. The number of soliton pulses operating in the dual-wavelength state is much larger than that of the single-wavelength state, while the pulse intensity always keeps constant. Experimental results reveal that the dual-wavelength mode locking is determined by the combination of pump strength and the cavity filtering effect.

Simultaneous orthogonal polarized dual-wavelength continuous-wave laser operation at 10795 nm and 10645 nm in Nd:YAlO_3 and their sum-frequency mixing

A dual-wavelength continuous-wave (cw) diode-end-pumped Nd:YAlO3 (Nd:YAP) laser that generates simultaneous laser at the wavelengths 1079.5 nm and 1064.5 nm is demonstrated. The optimum oscillation condition for the simultaneous orthogonal polarized dual-wavelength operation has been derived. A polarization beam splitter was placed in the cavity to split the beams polarizing in two orthogonal directions. We obtained a total power output over 6.5 W in two orthogonal polarized beam directions with 4.64 W in c-axis polarization and 1.86 W in a-axis polarization. Intracavity sum-frequency mixing at 1079.5 and 1064.5 nm was then realized in a KTiOPO4 (KTP) crystal to reach the green range. We obtained a cw output power of 1.12 W at 536 nm at the incident pump power of 17.3 W.

Quasi-three-level neodymium-doped yttrium aluminum garnet laser emitting at 885 nm

We present a diode-pumped quasi-three-level neodymium-doped yttrium aluminum garnet (Nd:YAG) laser at 885 nm, based on the 4F3/2-4I9/2 transition, generally used for a 946 nm emission. Combined with polarization components (Nd:YAG), the electro-optical crystal KH2PO4 (KDP) formed a Lyot filter in the cavity and compressed the available gain bandwidth. With an incident pump power of 9.2 W, a 714 mW continuous-wave (CW) output at 885 nm was achieved, and the optical-to-optical efficiency was 7.8%. With an adjustable voltage applied to the KDP crystal, the laser wavelength could be tuned from 885 nm to 884 nm. A simultaneous dual-wavelength Nd:YAG laser at 885 nm and 884 nm was also realized by adjusting the free spectral range of the Lyot filter. To our knowledge, it is the first study that has realized the tuning between the 884 and 885 nm lines and the simultaneous dual-wavelength CW laser operation at 885 nm and 884 nm.

Compact 584-nm light source based on sum-frequency mixing of diode pumped Nd:YLF lasers

A dual-wavelength continuous-wave (CW) diode end-pumped Nd:YLiF4 (Nd:YLF) laser that generates simultaneous laser action at the wavelengths 1047 and 1321 nm is demonstrated. A total output power of 350 mW for the dual-wavelength was achieved. Furthermore, intracavity sum-frequency mixing at 1047 and 1321 nm was then realized in a LBO crystal to reach the yellow-green range. We obtained a total CW output power of 34 mW at 584 nm.