Simultaneous Dual-wavelength Operation Research Articles

Spectrally narrowband simultaneous dual-wavelength emission from Y-branch DBR diode lasers at 785 nm

Y-branch distributed Bragg reflector (DBR) diode lasers with a stable narrowband emission in simultaneous dual-wavelength operation with spectral distances below 3.2 nm are presented. The Y-branch laser consists of two laser branches with different DBR gratings serving as wavelength-selective rear-side mirrors. Therefore, two emission wavelengths with a spectral distance defined by the DBR grating periods can be generated simultaneously. A Y-coupler combines the two ridge waveguide (RW) branches into a single straight output RW. Devices with a spectral distance of 0.6 nm and 2.0 nm emitting around 785 nm are manufactured. Selecting the operation parameters carefully, stable narrowband emission for both wavelengths is obtained. Resistors serving as heaters implemented next to the DBR gratings allow for wavelength adjustment and a tuning of the spectral distance. At an optical output power of 100 mW, the spectral distance can be shifted from 0 to 1.55 nm (0–0.76 THz) for the former device or from 1.00 to 3.15 nm (0.49–1.54 THz) for the latter device, respectively. This makes the Y-branch DBR diode laser particularly interesting for the generation of THz beat-note signals, needed to generate THz radiation via photo-mixing.

Comparative Study of Monolithic Integrated MMI-Coupler-Based Dual-Wavelength Lasers

We present AlGaAs-based monolithically integrated dual-wavelength lasers and master-oscillator power-amplifiers emitting around 785 nm which combine a near diffraction limited beam quality with single longitudinal mode emission, both achieved over a wide range of output powers. This holds for alternating dual wavelength operation which is of interest for applications in spectroscopy as well as for simultaneous dual wavelength operation which can be used to generate THz-radiation. Compared to previous designs the lateral optical confinement is provided by two differently deep etched ridge waveguides. Shallow etching is used in lasing and amplifying sections to ensure single-lateral mode operation, whereas deep etching is employed to form more compact S-bends and to enable the use of multi-mode interference (MMI) couplers instead of Y-couplers.

All-solid-state widely wavelength-tunable and high-efficiency Yb:YSr3(PO4)3 laser.

We demonstrate an all-solid-state widely wavelength-tunable Yb:YSr3(PO4)3 (Yb:YSP) laser with high efficiency. The free-running Yb:YSP laser oscillating at multiple wavelengths in the range of 1024-1054 nm is realized with different crystal lengths and output coupler transmittances. The maximum output power of 2.72 W is obtained under the absorption pump power of 7.30 W. The highest slope efficiency is 66.9%, using the crystal of 6.5-mm-length. Simultaneous dual-wavelength operation can be realized as well. Furthermore, the widely wavelength-tunable Yb:YSP laser with a range of more than 60 nm (from 1004 to 1066 nm) is achieved using a birefringent filter. The experimental results indicate that the Yb:YSP crystal can be a promising candidate for ultrafast lasers in the 1 µm region.

Tunable continuous-wave dual-wavelength laser operation of Pr3+:LiYF4 around 900 nm

We present here the first tunable continuous-wave (CW) simultaneous dual-wavelength laser operation of a Pr3+:LiYF4 crystal in the 900 nm spectral range using a single birefringent filter (BF) under excitation with a frequency doubled optically pumped semiconductor laser. By adjusting the rotation angle of the BF, the CW simultaneous dual-wavelength lasers operating at 869 and 915 nm, 894 and 915 nm, 915 and 923 nm, were obtained respectively.

Watt-level diode-pumped continuous-wave Pr:LiYF4 laser at 670 nm and simultaneous dual-wavelength operation at 639 and 670 nm.

We report on blue-diode-pumped continuous-wave Pr:LiYF4 (YLF) visible lasers involving a less investigated 670 nm laser emission. In the free-running regime, a simultaneous dual-wavelength operation at 670 and 639 nm is achieved with a maximum output power of 1.67 W and a slope efficiency of 20.4%. Using a Y3Al5O12 (YAG) plate as an intracavity etalon, we have suppressed the 639 nm emission, and then a single-wavelength laser at 670 nm has been achieved with a maximum output power of 0.96 W and slope efficiency of 12.7%. The directly generated 670 nm laser source from Pr:YLF crystal with watt-level output power has advantages over diode laser or frequency-doubled Nd:YVO4 lasers operating at a similar laser wavelength, which could be used in biomedical technologies.

Extending the wavelength tunability from 2.01 to 2.1 μm and simultaneous dual-wavelength operation at 2.05 and 2.3 μm in diode-pumped Tm:YLF lasers

We report on wavelength extension of diode-pumped Tm:YLF crystal lasers. Using specifically coated end-face mirrors, we have achieved a simulataneous dual-wavelength laser at 2.05 and 2.3 μm with a maximum output power up to 1.33 W and slope efficiency of about 9.7% in continuous-wave regime, for the first time to the best of our knowledge. Moreover, using an un-doped YAG etalon for wavelength tuning, the 2.05 μm lasing wavelength can be shifted to as far as 2.1 μm. We believe that it is the first time that a Tm:YLF laser has been wavelength extended to that far. Using a Cr:ZnSe saturable absorber, a passively Q-switched Tm:YLF laser at 2.05 μm has also attained with a maximum average output power of 0.66 W. The shortest pulse width is 91.7 ns at pulse repetition rate of 8.47 kHz. This work has extended the operating wavelengths of Tm3+ lasers to that in general for Ho3+ lasers, which could be practically meaningful for various applications.

High-efficiency diode-pumped continuous-wave and passively Q-switched c-cut Nd:LaMgAl11O19 (Nd:LMA) lasers

We report on diode-pumped continuous-wave and passively Q-switched c-cut Nd:LMA lasers. For continuous-wave operation, the maximum output power reaches 3.10 W with slope efficiency of about 48.9% at 1055 nm and 2.63 W with slope efficiency of 43.1% at 1082 nm. For passively Q switched operation, using a Cr:YAG as saturable absorber, the achieved maximum average output power is 1.49 W at 1055 nm with pulse width of 18.4 ns. Moreover, we have also realized simultaneous dual-wavelength laser operation at 1055 and 1082 nm with a maximum average output power of 1.22 W and a pulse width of 19.4 ns. Furthermore, inserting an etalon for suppressing the 1055 nm line, we have operated single wavelength laser at 1082 nm with output power of 0.31 W and pulse width of 20.8 ns. This work has verified the potential of Nd:LMA crystal as a laser gain medium.

Passively Q-switched Yb-doped dual-wavelength fiber laser based on a gold-nanocage saturable absorber.

In this paper, we demonstrate a passively Q-switched Yb-doped dual-wavelength fiber laser using gold nanocages (GNCs) as a saturable absorber. The GNCs are prepared by the seed-mediated method with modulation depth of 5.3% and saturable intensity of 0.16 MW/cm2. A simultaneous dual-wavelength operation is achieved at 1059.9 and 1060.5 nm with 3 dB bandwidths of 0.05 and 0.04 nm, respectively. A maximum average output power of 6.03 mW with minimum pulse width of 2.06 μs and maximum repetition rate of 134.9 kHz is obtained at a pump power of 385 mW, corresponding to optical-to-optical conversion efficiency of 1.57% and slope efficiency of 2.75%.

Continuous wave dual-wavelength Nd:YVO4 laser working at 1064 and 1066 nm

We demonstrate a continuous-wave (CW) dual-wavelength Nd:YVO4 laser working at 1064 and 1066 nm simultaneously. The method of Nd:YVO4 crystal angle tuning is used to balance the ratio of the stimulated emission cross sections of the two wavelengths, leading to the realization of a simultaneous dual-wavelength operation from only one laser. The experimental results show that at a 2.85 W pump power, the maximum output powers at wavelengths of 1064 and 1066 nm are 0.55 and 0.54 W, respectively. The linear resonate cavity is as short as 10 mm, which gives the laser the advantages of a miniature configuration and low threshold. Such a dual-wavelength laser can be very attractive for the development of compact THz sources based on difference frequency generation.

Quasi-three-level orthogonally polarized cw dual-wavelength operation in Nd:LiYF4

A diode-end-pumped quasi-three-level orthogonally polarized continuous-wave (cw) dual-wavelength Nd:LiYF4 (Nd:YLF) laser that generates simultaneous laser at the wavelengths 903nm and 908nm was demonstrated. Two types of cavity configurations were studied to support the stable dual-wavelength operation of the laser. A polarization beam splitter (PBS) was placed in the first type of cavity to split the beams polarizing in two orthogonal directions. At an absorbed pump power of 21.4W, the cw output power obtained at 903nm in π-polarization and 908nm in σ-polarization is 0.43W and 3.31W, respectively. Furthermore, in order to balance the gain-to-loss, an uncoated glass plane was inserted in the second type of cavity. By adjusting the inclination of the glass plane relative to the optical axis of the resonator, we realized the stable simultaneous dual-wavelength operation. The cw output powers of 1.82W at 903nm and of 2.92W at 908nm were obtained.

Full investigation into continuous-wave Nd:LuAG lasers on ^4F_3/2→^4I_13/2 transition around 13 and 14 μm

We report a full investigation of continuous-wave diode-pumped Nd:LuAG single crystal lasers on 4F3/2→4I13/2 transition around 1.3 and 1.4 μm. In free-running mode, a maximum output power of 4.18 W is achieved for a simultaneous dual-wavelength laser operation at 1321 and 1338 nm, which represents the highest output power for Nd:LuAG laser material at a 1.3 μm emission band. Three single wavelength lasers at 1340, 1332 and 1322 nm, as well as a dual-wavelength laser at 1334 and 1338 nm, are also generated with maximum output powers of 2.39, 2.63, 2.24 and 1.23 W, respectively, with the aid of a glass etalon. Moreover, a single wavelength laser at 1353 nm is also obtained with a maximum output power of 1.53 W. Furthermore, in free-running mode, simultaneous tri-wavelength eye-safe lasers at 1419, 1432 and 1442 nm are attained with a maximum output power of 1.83 W, and a 1.08 W single wavelength laser at 1419 nm is also yielded. Most of the 1.3 μm lasers and all of the 1.4 μm lasers are demonstrated for the first time to our knowledge. Thus, this work indicates that Nd:LuAG crystal is a very promising laser gain medium for high-power continuous-wave infrared laser generation.

Passively Q-Switched Nd,Cr:YAG Laser Simultaneous Dual-Wavelength Operation at 946 nm and 1.3 μm**Supported by the National Basic Research Program of China under Grant No 2013CB632704.

A diode-end-pumped Q-switched high-efficiency Nd,Cr:YAG laser with simultaneous dual-wavelength emission at 946nm and 1.3 μm is demonstrated. The maximum output power of 1.93 W with simultaneous dual-wavelength operation is achieved at an absorbed pump power of 13.32 W and an absorbed slope efficiency of 15.15%. The maximum optical-optical efficiency is 14.49% with pulse widths of 16.38 ns at 946 nm and 26.65 ns at 1.3 μm. A maximum total repetition rate of 43.25 kHz is obtained.

Dual-wavelength, passively Q-switched Tm:YAP laser with black phosphorus saturable absorber

A compact saturable absorber mirror (SAM) based on multi-layered black phosphorus (BP) nanoplatelets was fabricated and successfully used as an efficient saturable absorber (SA) in a passively Q-switched Tm:YAP laser at 1.9 μm. With the BP SAM, Q-switched pulses with duration of 181 ns and average output power of 3.1 W were generated at a pulse repetition rate of 81 kHz, resulting in a pulse energy of 39.5 μJ, to the best of our knowledge, which is the record among the reports on BP SA-based Q-switched lasers. In addition, the simultaneous dual-wavelength Q-switched operation at both 1969 and 1979 nm has been observed. The results indicate the promising potential of multi-layered BP nanoplatelets as SAs for achieving efficient pulsed lasers at around 2 μm.

Single- and dual-wavelength laser operation of a diode-pumped Nd:LaF3 single crystal around 1.05 μm and 1.32 μm

Calibrated room temperature polarized emission spectra recorded between 850 and 1400 nm and nearly free from any reabsorption effect are presented for the first time. A laser output power of 2.35 W is obtained at 1063.45 nm with a laser slope efficiency of about 56% by pumping an uncoated Nd:LaF3 single crystal with a fiber-coupled laser diode at 790 nm inside a standard two-mirror linear laser cavity. True dual-wavelength laser operation on two orthogonally polarized laser lines around 1040 and 1065 nm as well as continuous laser wavelength tuning around 1040 nm, 1048 nm and 1064 nm are also achieved for the first time by using either an intracavity etalon or a birefringent filter. Laser operation is finally obtained around 1330.73 nm with a maximum output power of 0.18 W and a laser slope efficiency of about 4% and simultaneous dual-wavelength laser operation at 1329.04 and 1359.67 nm is demonstrated by using a glass etalon.

Frequency domain near-infrared multiwavelength imager design using high-speed, direct analog-to-digital conversion.

Frequency domain near-infrared spectroscopy (FD-NIRS) has proven to be a reliable method for quantification of tissue absolute optical properties. We present a full-sampling direct analog-to-digital conversion FD-NIR imager. While we developed this instrument with a focus on high-speed optical breast tomographic imaging, the proposed design is suitable for a wide-range of biophotonic applications where fast, accurate quantification of absolute optical properties is needed. Simultaneous dual wavelength operation at 685 and 830 nm is achieved by concurrent 67.5 and 75 MHz frequency modulation of each laser source, respectively, followed by digitization using a high-speed (180 MS/s) 16-bit A/D converter and hybrid FPGA-assisted demodulation. The instrument supports 25 source locations and features 20 concurrently operating detectors. The noise floor of the instrument was measured at <1.4 pW/√Hz, and a dynamic range of 115+ dB, corresponding to nearly six orders of magnitude, has been demonstrated. Titration experiments consisting of 200 different absorption and scattering values were conducted to demonstrate accurate optical property quantification over the entire range of physiologically expected values.

Diode-pumped Pr3+:LiYF4 visible dual-wavelength laser

A diode-pumped simultaneous continuous-wave (cw) dual-wavelength Pr3+:LiYF4 laser in the green spectral region is experimentally demonstrated. We calculate the condition of gain-to-loss balance via an uncoated glass plane to achieve the simultaneous dual-wavelength operation. The simultaneous dual-wavelength Pr3+:LiYF4 laser at 546nm in π-polarization and 550nm in σ-polarization is experimentally realized. At an absorbed pump power of 1.5W, the maximum output power obtained at 546nm and 550nm is 184mW and 158mW, respectively.

2.4 W highly efficient simultaneous dual-wavelength laser operation of monoclinic Yb(3+):Ca4LaO(BO3)3 crystals.

We have studied the simultaneous dual-wavelength laser operation of the X-cut, Y-cut, and Z-cut Yb(3+):Ca4LaO(BO3)3 crystals for the first time to the best of our knowledge. We analyzed the dual-wavelength laser output power and emission spectra under several output coupler transmittances. The stable dual-wavelength lasers were generated by adjusting the laser elements. A dual-wavelength laser output power 2.46 W was obtained with a slope efficiency of 67.5% by employing the Y-cut crystal at 1029 and 1036 nm. The two wavelengths had nearly the same relative intensity. The two different emission wavelengths were found to change with crystal direction and output coupler transmittance. This laser has a possible application as the laser source in the generation of different terahertz waves.

Studies on simultaneous dual wavelength operation at 912.2nm and 914nm from dual gain diode-pumped Nd3+ doped vanadate laser

Abstract A laser is constructed comprising of Nd 3+ doped yttrium vanadate (Nd:YVO 4 ) and gadolinium vanadate (Nd:GdVO 4 ) in order to obtain simultaneous dual wavelength operation at 914 nm and 912 nm emitted by the respective crystals under 4 F 3/2 → 4 I 9/2 laser transitions. The performance of the laser is studied experimentally and analyzed using laser rate equation model incorporating the cross saturation terms. The simulated trend of variation of output power at 912 and 914 nm as a function of pump power agrees reasonably well with the experimental data and confirms that the saturation of gain at Nd:GdVO 4 crystal by the 914 nm is much stronger than the saturation of gain at Nd:YVO 4 crystal by the 912 nm. It has been found that to obtain simultaneous dual wavelength operation the relative gain at the Nd:GdVO 4 crystal should be considerably higher than that at the Nd:YVO 4 crystal. At a pump power of 29.7 W and 22.6 W applied to Nd:GdVO 4 and Nd:YVO 4 crystals respectively, 1.3 W of output power at 912.2 nm and 1.7 W of output power at 914 nm was obtained simultaneously. The frequency difference of the two wavelengths is 0.73 THz and the state of polarization of the two wavelengths can be easily varied by changing the relative orientation of the c -axes of the crystals.

Diode-Pumped Quasi-Three-Level ${\rm Nd}{:}{\rm YVO}_{4}$ Laser With Orthogonally Polarized Emission

A diode-end-pumped quasi-three-level orthogonally polarized continuous-wave dual-wavelength Nd:YVO4 laser was demonstrated. We analyze the condition of gain-to-loss balance via an uncoated glass plane to achieve the simultaneous dual-wavelength operation. We experimentally demonstrate the orthogonally polarized dual-wavelength laser with a Nd:YVO4 crystal. The simultaneous dual-wavelength Nd:YVO4 laser at 914 nm in π-polarization and 915 nm in σ-polarization is realized. At an incident pump power of 12 W, the output power obtained at 914 and 915 nm is 1.19 and 0.86 W, respectively. To the best of our knowledge, this is the first work realizing quasi-three-level orthogonally polarized dual-wavelength operation in Nd-doped lasers.

Simultaneous dual-wavelength operation around 1.06 μm of a LD-end-pumped, passively Q-switched Nd:GGG laser with GaAs as saturable absorber

By using neodymium-doped gadolinium gallium garnet (Nd:GGG) as the laser medium, a passively Q-switched simultaneous dual-wavelength Nd:GGG laser with a GaAs saturable absorber has been realized. The Nd:GGG laser operates at a stable dual-wavelength peaked at 1060.8 and 1062.7 nm without any wavelength selective elements in the cavity. Stable Q-switched pulses with a shortest duration of 6 ns have been obtained, corresponding to a single pulse energy of 2.1 μJ and a peak power of 335 W.