Dual-wavelength Ti Research Articles

Single laser-based differential absorption lidar (DIAL) for remote profiling atmospheric oxygen

Recently, we have demonstrated a longitudinally pumped tunable dual-wavelength Ti:sapphire laser that can operate at simultaneous dual-wavelength (765.0, 771.3 nm), (763.9, 772.2 nm), (763.5, 772.2 nm) and (762.4, 773.7 nm) with a pulse width of ∼20 ns and a maximum average power of ∼2.98 W at 1-kHz pulse repetition rate, corresponding to a slope efficiency of ∼34.7% [1]. In this paper, the feasibility of the contactless differential absorption lidar (DIAL) equipped with the dual-wavelength laser emitting at 762 nm (on-wavelength) and 773 nm (off-wavelength) on remote 3D-measurement of molecular oxygen, O2, has been investigated. Absorption by atmospheric oxygen A-band at 761.9 nm corresponds to the magnetic dipole transition b1Σb+(v′=0)←X3Σg−(v″=0) with absorption cross section of 5.749 × 10−3 cm−2 atm−1 at STP. The accuracy and dynamic range of the DIAL measurement can be extended by simultaneous transmission and detection the spectrally close “on” and “off” wavelengths generated in a compact single laser, in addition to reduce the cost, volume, and weight of the system. The results demonstrate that a concentration of less than 1 ppm by volume is detectable by the system if a path length of 1 km is used. It is noticeable that the wavelengths 762 nm and 773 nm in the near-infrared window spectral range (650–950 nm) allow lidar system to monitor dissolved oxygen in ambient water. This system can also be used from a satellite to quickly characterize O2 in H2O matrices in the outer solar system bodies.

Tunable single- and dual-wavelength nanosecond Ti:Sapphire laser around 765 nm

We report on the longitudinally pumped tunable single- and dual-wavelength nanosecond Ti:Sapphire laser operation around 765 nm by using a Brewster-cut single Ti:Sapphire crystal in combination with an intracavity prism and etalon. Tilting the etalon to a specific angle, single-wavelength operation at 767.9 nm is achieved first, with a maximum output power value of 1.3 W below 5.5 W pump power. Then, increasing the pump power leads to simultaneously operation at dual wavelength (765.0, 771.3 nm), (763.9, 772.2 nm), (763.5, 772.2 nm), and (762.4, 773.7 nm) with a maximum output power of ~ 2.98 W, pulse width of ~ 20 ns, and a laser slope efficiency of about 34.7% at 1 kHz repetition rate. By tilting the etalon, other dual- and single-wavelength laser operations could be achieved. Experimental results show that it is tunable in the region 750–840 nm which here is limited by the reflectivity of the cavity mirrors. We observed, when laser oscillates at dual wavelength, the separation of the wavelengths increased with pump power which could be because of thermal lensing in Ti:Sapphire. The output characteristics versus incident pump power at 1 and 5 kHz repetition rate show output power increases linearly with incident pump power with similar slope for both 1 and 5 kHz repetition rates, whereas pump threshold increased in the case of 5 kHz.

Design of efficient single-stage chirped pulse difference frequency generation at 7 μm, driven by a dual wavelength Ti:sapphire laser

We present a design for a high-energy single stage mid-IR difference frequency generation adapted to a two-color Ti:sapphire amplifier system. The optimized mixing process is based on chirped pulse difference frequency generation (CP-DFG), allowing for a higher conversion efficiency, larger bandwidth and reduced two photon absorption losses. The numerical start-to-end simulations include stretching, chirped pulse difference frequency generation and pulse compression. Realistic design parameters for commercially available non linear crystals (GaSe, AgGaS2, LiInSe2, LiGaSe2) are considered. Compared to conventional un-chirped DFG directly pumped by Ti:sapphire technology we report a threefold increase of the quantum efficiency. Our CP-DFG scheme provides up to 340 {\mu}J pulse energy directly at 7.2 {\mu}m when pumped with 3 mJ and supports a bandwidth of up to 350 nm. The resulting 240 fs mid-IR pulses are inherently phase stable.

Two Synchronized Operating Modes of Femtosecond and Picosecond Pulses in a Dual-Wavelength Laser

Two synchronized operating modes of femtosecond and picosecond pulses, cross mode-locking and multi-pulse operating, are presented in a two-beam-pumped dual-wavelength Ti:sapphire laser. For the cross mode-locking mode, synchronized laser pulses of 37.5 fs and 0.891ps, with a timing jitter of 139 fs, are obtained in the femtosecond cavity and picosecond cavity, respectively. For the multi-pulse mode, pulses of 35 fs are obtained in the femtosecond cavity, whereas, multi-pulse mode appears in the picosecond cavity, with a pulse envelope width of 1.06 ps. The two operating modes can be switched from one to the other, dominated mainly by the mutual interaction between cross-phase modulation and self-amplitude modulation.

High energy femtosecond mid-infrared generation pumped by a two-color Ti:sapphire multipass amplifier

Intense mid-infrared was generated by direct frequency mixing two pulses from a dual-wavelength Ti:sapphire system. From a multipass amplifier we generated two tunable wavelength femtosecond pulses with a total energy of 15 mJ. Pulse energy of 1.6 μJ and 7.4 μJ of mid-infrared light is achieved with and without its multipass amplifier at 9–11 μm, with pulse duration of 500 fs.

An all-solid-state high power quasi-continuous-wave tunable dual-wavelength Ti:sapphire laser system using birefringence filter

This paper describes a tunable dual-wavelength Ti:sapphire laser system with quasi-continuous-wave and high-power outputs. In the design of the laser, it adopts a frequency-doubled Nd:YAG laser as the pumping source, and the birefringence filter as the tuning element. Tunable dual-wavelength outputs with one wavelength range from 700 nm to 756.5 nm, another from 830 nm to 900mn have been demonstrated. With a pump power of 23 W at 532 nm, a repetition rate of 7 kHz and a pulse width of 47.6 ns, an output power of 5.1 W at 744.8 nm and 860.9 nm with a pulse width of 13.2 ns and a line width of 3 nm has been obtained, it indicates an optical-to-optical conversion efficiency of 22.2%.

An All-Solid-State Tunable Dual-Wavelength Ti:Sapphire Laser withQuasi-Continuous-Wave Outputs

A high power dual-wavelength Ti:sapphire laser system with wide turningrange and high efficiency is described, which consists of twoprism-dispersed resonators pumped by an all-solid-statefrequency-doubled Nd:YAG laser. Tunable dual-wavelength outputs, withone wavelength range from 750 nm to 795 nm and the other from 800 nm to850 nm, have been demonstrated. With a pump power of 23 W at 532 nm, arepetition rate of 6.5 kHz and a pulse width of 67.6 ns, the maximumdual-wavelength output power of 5.6 W at 785.3 nm and 812.1 nm, with apulse width of 17.2 ns and a line width of 2 nm, has been achieved,leading to an optical-to-optical conversion efficiency of 24.4%.

Automatic continuous scanning and random-access switching of mid-infrared waves generated by difference-frequency mixing

We report the rapid tuning of mid-infrared waves beyond 5 microm emitted in difference-frequency mixing with an electronically tuned dual-wavelength Ti:Al2O3 laser used as a pumping source. Simultaneous rapid tuning of the dual wavelengths, which satisfy phase matching in AgGaS2, allows rapid random access switching and continuous tuning of mid-infrared wavelengths. In random-access switching, the mid-infrared wavelength is tuned every pulse shot at a repetition rate of 1 kHz. Mid-infrared wavelengths continuously tuned from 5.2 to 7.2 microm, from 7.0 to 9.1 microm, and from 8.9 to 12.0 microm are achieved at phase-matched angles of 55 degrees, 50 degrees, and 45 degrees, respectively.

Generation and evaluation of synchronous femtosecond and picosecond pulses in a dual-wavelength Ti:sapphire laser

We obtain synchronous femtosecond and picosecond laser pulses by achieving cross mode locking in a double-cavity dual-wavelength femtosecond Ti:sapphire laser. The autocorrelations and the crosscorrelation show that the femtosecond and picosecond pulses are well synchronized, with a timing jitter less than 200 fs. Independent self mode locking in each laser cavity is governed mainly by group-velocity dispersion and self-phase modulation, whereas cross mode locking is dominated primarily by cross-phase modulation and gain competition. Meanwhile, FWHM and rms formalisms are compared and further utilized to characterize laser pulses. In addition, the timing jitter and the tuning range of the laser are analyzed and identified.

Generation of vacuum-ultraviolet light by an optically contacted, prism-coupled KBe2BO3F2 crystal.

We have demonstrated the second harmonic of a frequency-tripled Nd:YVO4 laser with 2.5-mW quasi-cw output by using an optically contacted, prism-coupled KBe2BO3F2 crystal. We also achieved the second harmonic with a frequency-doubled single-mode Ti:sapphire laser at 172.5 nm and sum-frequency mixing with a dual-wavelength Ti:sapphire laser at 163.3 nm. These wavelengths are to our knowledge the shortest obtained by use of nonlinear crystals for second-harmonic generation and sum-frequency mixing, respectively.

Multifrequency parametric infrared Raman generation in KGd(WO_4)_2 crystal with biharmonic ultrashort-pulse pumping

Mutlifrequency parametric Raman generation was carried out in a KGd(WO(4))(2) crystal by use of a dual-wavelength Ti:sapphire laser system. It was found that with femtosecond pump pulses the efficiency of Raman generation is low because of the onset of self-phase modulation. The mechanism for suppression of stimulated Raman scattering by self-phase modulation is discussed. Employing 2-ps-long chirped pulses generated four Stokes and one anti-Stokes component.

Development of a dual-wavelength Ti:sapphire multi-pass amplifier and its application to intense mid-infrared generation

We demonstrate the amplification of two tunable wavelength pulses from a dual-wavelength Ti:sapphire laser system to generate a total energy of 15 mJ. Mid-infrared pulses were generated by difference frequency mixing the two intense outputs, in an AgGaS 2 nonlinear crystal. Pulse energy of 7.4 μJ was achieved at mid-infrared wavelengths of ∼10 μm.

Mid-infrared pulses generated from the mixing output of an amplified, dual-wavelength Ti:sapphire system

We demonstrate the generation of femtosecond mid-infrared pulses by direct difference-frequency mixing in a AgGaS(2) crystal of two intense pulses from a dual-wavelength oscillator that have been simultaneously amplified in a single regenerative amplifier. A pulse energy of as much as 1.6 muJ was achieved at wavelengths of 9-11 mum.

Rate-equation theory and experimental research on dual-wavelength operation of a Ti:sapphire laser

Rate-equation analysis and experiments on a pulsed dual-wavelength Ti:sapphire laser are reported in the paper. A four-energy-level system with two lower-energy levels is put forward and numerical calculations are given. A simple optical setup with two sub-resonators is constructed, which yields a total energy from dual-wavelength lasers up to 41.8 mJ. The largest tunable range is over 110 nm. Laser characteristics of dual-wavelength pulses are observed. Experimental results are in accord with rate-equation-theory results.

Dual-wavelength diode-seeded Ti:sapphire laser for differential absorption lidar applications

A dual-wavelength, diode-seeded, flash-lamp-pumped Ti:sapphire laser system has been developed. Injection seeding allowed the attainment of high output energies (130 mJ), narrow linewidth (250 MHz), and high reliability. Furthermore, an original method is presented for dual-wavelength operation, using diode current sweeping. These specifications are ideal for differential absorption lidar applications, and the example of NO(2) detection is presented. Extension to other pollutants is discussed.