Continuous-wave Ti Research Articles

Room-temperature laser operation at 1.8 μm in Tm:GdVO4 waveguides

We report on the first experimentally demonstrated Tm-doped gadolinium vanadate waveguide laser operating at 1.8 μm. Cladding waveguides with a diameter of 60 μm are fabricated by femtosecond laser direct writing (FsLDW) in 3 at. % Tm:GdVO4 crystal. A continuous-wave (CW) Ti:sapphire laser is used as the pump source for waveguide laser generation. The impacts of waveguide lengths and cavity conditions on the obtained lasing performance are well studied. For the Tm:GdVO4 waveguide with a total length of 2.8 mm, the laser output at 1812 nm is achieved with a lasing threshold of 116.6 mW and a slope efficiency of 23.2% when utilizing the π-polarized pump source at 799 nm. And the maximum output power of 179 mW is determined at a pump power of 932 mW, which corresponds to an overall optical-to-optical efficiency of 19.2%. The experimental results achieved in this work suggests that compact and low-threshold Tm:GdVO4 waveguide lasers can be very promising for applications in mid-infrared photonic devices with compact structures.

Polymorphism and up-conversion photoluminescence properties of Y2WO6 doped with Yb3+/Er3+ under excitation at 975 nm

This article reports the synthesis and luminescent properties (up-conversion and down-shifting) of the tetragonal and orthorhombic polymorphs of Y2WO6 doped with Erbium (Er3+) and Ytterbium (Yb3+) cations. The syntheses were carried out by a high temperature solid state reaction. The orthorhombic phase was prepared by pressing the parent compounds into pellets of 13 mm diameter. The samples were characterized by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). Luminescence up-conversion measurements were analyzed using a tunable continuous wave (CW) Ti:sapphire laser system tuned at 975 nm. The results show that the green up-conversion emission is more intense than the red one in both polymorphs. To gain further clarity on this matter, we have also conducted a study on down-shifting emission spectra measured at 378 nm, where only the strong green emission is observed. The pump power dependence and the decay curves of the (4S3/2 → 4I15/2) transition were also evaluated.

A frequency comb stabilized Ti:Sa laser as a self-reference for ion-trap experiments with a 40Ca+ ion.

In this study, we report on the stabilization of a continuous-wave Ti:Sa laser to an optical frequency comb. The laser is emitting at 866nm to address one of the transitions required for Doppler cooling of a single 40Ca+ ion in a linear Paul trap (2D3/2 ↔P1/22). The stabilized Ti:Sa laser is utilized to calibrate an ultra-accurate wavelength meter. We certify this self-reference laser source by comparing the results from monitoring the laser-cooled 40Ca+ ion in the linear Paul trap, with those obtained when a HeNe laser is used for calibration. The use of this self-reference is compatible with the simultaneous use of the comb for precision spectroscopy in the same ion-trap experiment.

High-Efficiency Continuous-Wave Ti:Sapphire Laser with High-Intensity Pumping Using a Commercially Available Crystal

Despite the importance of improving the efficiency of lasers in order to expand their utility range, the improvement of the efficiency of Ti:sapphire lasers has not progressed due to their high crystal losses. Therefore, we improved the efficiency of CW Ti:sapphire lasers by high-intensity pumping, which is one of the most effective methods of suppressing the efficiency reduction due to losses. Using a easily commercially available 0.25 wt.%, figure of merit (FOM) 200 Ti:sapphire crystal, optics and a pump source, we achieved an optical-to-optical conversion efficiency of 32.4% with a slope efficiency of 42.5% at an incident pump power of 5.0 W which corresponds the maximum pumping intensity of 860 kW/cm2. Furthermore, we ensured the reliability of our theoretical analysis by reproducing the experimental results. From this reliable theory, double-pass pumping and increasing the pump power to 25 W resulted in the highest optical-to-optical conversion and slope efficiencies for the incident pump power of 55.9% and 59.6%, respectively, at a high intrinsic residual loss of 4.0%. Even if losses doubled or deviated from the optimum condition for the highest efficiency, the efficiency reduction due to these factors was only a few percent. These results show that with high-intensity pumping, lasers with efficiencies well exceeding half of the quantum limit can be achieved even if all components, including Ti:sapphire crystals, are easily commercially available.

Modulation-Noise-Free Continuously Tunable Single-Frequency CW Ti:Sapphire Laser With Intracavity-Locked Birefringent Etalon

We present a continuously tunable single-frequency continuous wave (CW) Ti:Sapphire (Ti:S) laser with modulation-free-locked intracavity lithium niobate (LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) birefringent etalon (BE), which is implemented by detecting the polarization state variation of the reflected laser beam from the BE. After the BE is stably locked, the continuous frequency-scanning range up to 40 GHz is obtained within the tuning range of 300 nm while the resonator length of the Ti:S laser is continuously scanned. Because the modulation signal is unnecessary in the presented Ti:S laser system, the influences of the extra modulation signal on the intensity noise as well as the frequency noise of the laser are thoroughly eliminated and the modulation-noise-free continuously tunable single-frequency CW Ti:S laser is successfully attained.

725 nm watt-level injection-locked continuous-wave Ti:sapphire laser for a mercury optical lattice clock.

We develop a watt-level 725 nm continuous-wave tunable narrow linewidth injection-locked Ti:sapphire laser. The seed laser is frequency-locked on a Fabry-Perot cavity to narrow the linewidth and stabilize the frequency. Because the wavelength of the seed laser is located at the edge of the gain profile of the Ti:sapphire crystal, it is difficult to injection-lock the Ti:sapphire laser at 725 nm. A cavity mirror, which has a long-pass-filter coating with a sharp edge, is used in the Ti:sapphire cavity to suppress mode competition from the long wavelength side. This method effectively reduces the power requirement of the seed laser at 725 nm, and the Ti:sapphire laser can be injection-locked at higher output power. As a result, a 1 W output power with a 27% slope efficiency is achieved in the injection-locked laser, and a 210 mW UV laser is obtained in a subsequent second-harmonic generation stage. To the best of our knowledge, this is the shortest wavelength for the watt-level injection-locked continuous-wave Ti:sapphire laser. This laser will be used in a mercury optical lattice clock in the future.

Theoretical analysis of a high efficiency blue-laser-diode-pumped Ti:sapphire laser by high intensity pumping

We report on an efficiency increase for blue laser diode (LD) pumped continuous-wave (CW) Ti:sapphire lasers. We theoretically analyzed our experimental results and previous research and clarified the reliability of our theoretical model. Furthermore, we analyzed the optical-to-optical conversion efficiency of blue LD pumped CW Ti:sapphire lasers by using this theoretical model. As a result of the analysis, we found that the highest efficiency of 22.4% could be achieved with blue LD pumped CW Ti:sapphire lasers by using high intensity pumping and through our optimizations. To the best of our knowledge, this efficiency reaches the equivalent efficiency of the highest efficiency of green LD pumped CW Ti:sapphire lasers. According to previous research, improving blue LD pumped Ti:sapphire laser efficiency is challenging. Nevertheless, our analysis clarified that efficiency increases for blue LD pumped CW Ti:sapphire lasers can be achieved.

Low-threshold-intensity 3.8-W continuous-wave Ti:Sapphire oscillator directly pumped with green diodes

Low-threshold-intensity 3.8-W continuous-wave Ti:Sapphire oscillator directly pumped with green diodes

Watt-Level CW Ti: Sapphire Oscillator Directly Pumped With Green Laser Diodes Module

A watt-level directly diode-pumped continuous-wave (CW) Ti:Sapphire oscillator was demonstrated for the first breakthrough by a high-power green laser-diode-pumped module employing the technologies of beam shaping, beam collimation, polarization beam combining, and fiber coupling. A 1.36-W output power and 10.6% of slope efficiency were obtained based on the double-concave (DC) cavity configuration. This is the highest CW output power from Ti:Sapphire (Ti:S) oscillator directly pumped by green laser diodes (LDs) reported so far.

A direct diode pumped Ti:sapphire laser with single-frequency operation for high resolution spectroscopy

A direct diode pumped continuous-wave Ti:sapphire laser (DDPTS) is presented. A bow-tie geometry with optical diode is chosen for unidirectional single-mode operation. Frequency selection is performed with a standard combination of birefringent filter and etalon. To accomplish mode-hop free frequency tuning the piezo-driven etalon is stabilized to one of the cavity modes via dither-locking method. To suppress environmental fluctuations the cavity-mode is additionally locked to an external optical cavity with low frequency drift. Feasibility of the setup for high-resolution spectroscopy is demonstrated by saturated absorption spectroscopy of the D2 line of Rubidium.

Pushing the limits of deep-ultraviolet scanning near-field optical microscopy

Deep-ultraviolet (DUV) microscopy and microspectroscopy have received much attention in label-free live-cell imaging, selective molecular analysis, and optical characterizations of ultrawide bandgap materials. Far-field optics approaches usually suffer from the diffraction limit of light. Meanwhile, near-field optics technology is immature in the DUV spectral region. Herein, we develop a DUV scanning near-field optical microscope (SNOM) with an excitation wavelength of 210 nm. The fourth harmonic generation of a continuous-wave Ti:sapphire laser is the excitation source. Two negative feedback control systems stabilize the power and pointing, allowing scanning microscopy to be carried out over a long period of time even in the DUV spectral region. A reflective objective couples the excitation beam onto an optical fiber probe. The optical fiber probe is solarization-resistant and is not coated by metallic materials. The reflective-based objective optical design does not introduce chromatic aberrations in the detection signals. Our DUV-SNOM is used to measure the photoluminescence (PL) spectra of the quantum well structure of aluminum gallium nitride, which is an ultrawide bandgap material. The PL mapping images indicate that emissive localization centers can be individually visualized via our DUV-SNOM with a lateral resolution exceeding 150 nm.

A direct diode pumped continuous-wave Ti:sapphire laser as seed of a pulsed amplifier for high-resolution resonance ionization spectroscopy

Progress of the development of a tunable continuous-wave directly diode-pumped Ti:sapphire laser is reported. The pump diode system based on InGaN multimode emitters in the blue-green wavelength region is characterized in terms of beam quality and output power. A prototype bow-tie resonator with a short highly doped Brewster-cut Ti:sapphire crystal was investigated. Output power scaling with the number of pump diodes and output coupling ratio as well as wavelength tuning range using a three-plate birefringent filter was measured.

Continuous-wave difference-frequency generation based on BaGa4Se7 crystal.

A continuous-wave mid-infrared radiation from difference frequency generation by mixing a continuous-wave Ti: sapphire laser and a continuous-wave YAG laser in a 15 mm long BaGa4Se7 crystal is demonstrated for the first time. The tunable range from 3.15 to 7.92 μm was achieved by rotating the crystal to fulfill the type I phase-matching condition. A maximum DFG power of 1.41 μW was obtained at 5 μm. Meanwhile the experimental DFG power conversion efficiency was 20.2 μW/W2, with a length-normalized slope efficiency of 15.5 μW/cmW2. The conversion efficiency decreases rapidly from 50 μW/cmW2 at 3.15 μm to 1 μW/cmW2 at 7.92 μm. The wavelength acceptance bandwidth and the angular acceptance bandwidth were measured to be 16.4 cm-1 and 44' for DFG at 5.1 μm, respectively.

Influence on the Lifetime of 87Rb Bose–Einstein Condensation for Far-Detuning Single-Frequency Lasers with Different Phase Noises**Supported by the National Key Research and Development Program of China under Grant Nos 2016YFA0301600 and 2016YFA0301602, the National Natural Science Foundation of China under Grant Nos 11234008, 11474188 and 11704234, and the Fund for Shanxi ‘1331 Project’ Key Subjects Construction.

We study the influence of the phase noises of far detuning single frequency lasers on the lifetime of Bose–Einstein condensation (BEC) of 87Rb in an optical dipole trap. As a comparison, we shine a continuous-wave single-frequency Ti:sapphire laser, an external-cavity diode laser and a phase-locked diode laser on BEC. We measure the heating and lifetime of BEC in two different hyperfine states: and . Due to the narrow linewidth and small phase noise, the continuous-wave single-frequency Ti:sapphire laser has less influence on the lifetime of 87Rb BEC than the external-cavity diode laser. To reduce the phase noise of the external-cavity diode laser, we use an optical phase-locked loop for the external-cavity diode laser to be locked on a Ti:sapphire laser. The lifetime of BEC is increased when applying the phase-locked diode laser in contrast with the external-cavity diode laser.

Self-injection locked CW single-frequency tunable Ti:sapphire laser.

A self-injection locked continuous-wave (CW) single-frequency tunable Ti:sapphire laser is demonstrated in this paper. Unidirectional operation of the presented Ti:sapphire laser is achieved by using a retro-reflecting device which can retro-reflect a seed laser beam from one direction back into the counter-propagating field. On the basis, the influence of the transmission of output coupler on the unidirectional operation is investigated and it is found that stable unidirectional and single-frequency operation of the Ti:sapphire laser is achieved when the loss difference between both output directions is larger than a certain value, which is easy to be realized by choosing the transmission of output coupler. When the output coupler with transmission of 6.5% is utilized, the maximal 5 W CW single-frequency Ti:sapphire laser with stable unidirectional operation is obtained with the pump power of 18 W. The measured power stability and M2 are better than ±0.9% and 1.1, respectively. The maximal tuning range and continuous frequency-tuning ability are 120 nm and 40.75 GHz, respectively.

1.9 µm waveguide laser fabricated by ultrafast laser inscription in Tm:Lu2O3 ceramic.

The ultrafast laser inscription technique has been used to fabricate channel waveguides in Tm3+-doped Lu2O3 ceramic gain medium for the first time to our knowledge. Laser operation has been demonstrated using a monolithic microchip cavity with a continuous-wave Ti:sapphire pump source at 796 nm. The maximum output power achieved from the Tm:Lu2O3 waveguide laser was 81 mW at 1942 nm. A maximum slope efficiency of 9.5% was measured with the laser thresholds observed to be in the range of 50-200 mW of absorbed pump power. Propagation losses for this waveguide structure are calculated to be 0.7 dB⋅cm-1 ± 0.3 dB⋅cm-1 at the lasing wavelength.

Rainbow Stars—Multi-Color Laser Emission for Science and Art

Rainbow Stars—Multi-Color Laser Emission for Science and Art

High-resolution spectroscopy of laser ablation plumes using laser-induced fluorescence

We report laser-induced fluorescence spectroscopy (LIF) of laser-produced plasmas under varying nitrogen pressure levels up to atmospheric pressure. The plasmas were generated on a glass target containing minor amounts of U and Al using 1064 nm, 6 ns pulses from a Nd:YAG laser. A frequency-doubled continuous-wave Ti:Sapphire laser was used as an ultra-narrowband tunable LIF excitation source to increase the magnitude and persistence of emission from selected U and Al atomic transitions in a laser-produced plasma. 2D-fluorescence spectroscopy (2D-FS) absorption/emission images were recorded at various nitrogen pressure levels, showing both excitation and emission spectral features. At lower pressure levels (⪝100 Torr), fluorescence emission was found to be well separated in time from thermally-excited emission. However, as the ambient pressure increased, the thermally-excited emission persisted for longer times along with a reduction of LIF emission persistence and intensity. The excitation spectral features showed the inherent linewidths of various transitions in the plasma, which have significantly narrower spectral linewidths than observed in emission spectra. We evaluated two nearby transitions separated by only 18 pm to demonstrate the effectiveness of fluorescence spectra over thermally-excited spectra for high-resolution studies. The present results highlight the importance of LIF as a diagnostic tool employing continuous-wave laser re-excitation, addressing some of the limitations of traditional emission and absorption spectroscopic methods.

Two-dimensional fluorescence spectroscopy of laser-produced plasmas.

We use a two-dimensional laser-induced fluorescence spectroscopy technique to measure the coupled absorption and emission properties of atomic species in plasmas produced via laser ablation of a solid aluminum target at atmospheric pressure. Emission spectra from the Al I 394.4nm and Al I 396.15nm transitions are measured while a frequency-doubled, continuous wave (cw) Ti:sapphire laser is tuned across the Al I 396.15nm transition. The resulting two-dimensional spectra show the energy coupling between the two transitions via increased emission intensity for both transitions during resonant absorption of the cw laser at one transition. Time-delayed, gated detection of the emission spectrum is used to isolate resonantly excited fluorescence emission from thermally excited emission from the plasma. In addition, the tunable cw laser measures the absorption spectrum of the Al transition with ultrahigh resolution after the plasma has cooled, resulting in narrower spectral linewidths than observed in emission spectra. Our results highlight that fluorescence spectroscopy employing cw laser re-excitation after pulsed laser ablation combines benefits of both traditional emission and absorption spectroscopic methods.

Comparison and characterization of efficient frequency doubling at 397.5 nm with PPKTP, LBO and BiBO crystals

A continuous-wave Ti:sapphire laser at 795 nm is frequency doubled in a bow-tie type enhancement four-mirror ring cavity with LiB3O5 (LBO), BiB3O6 (BiBO), and periodically polled KTiOPO4 (PPKTP) crystals, respectively. The properties of 397.5 nm ultra-violet (UV) output power, beam quality, stability for these different nonlinear crystals are investigated and compared. For PPKTP crystal, the highest doubling efficiency of 58.1% is achieved from 191 mW of 795 nm mode-matched fundamental power to 111 mW of 397.5 nm UV output. For LBO crystal, with 1.34 W of mode-matched 795 nm power, 770 mW of 397.5 nm UV output is achieved, implying a doubling efficiency of 57.4%. For BiBO crystal, with 323 mW of mode-matched 795 nm power, 116 mW of 397.5 nm UV output is achieved, leading to a doubling efficiency of 35.9%. The generated UV radiation has potential applications in the fields of quantum physics.