We report on a new longwave infrared optical parametric source, and its implementation for long range or medium range standoff detection of gaseous chemical warfare agents.
We report on a longwave infrared lidar, tailored for detection of chemical warfare agents in the gaseous phase. The emitter is based on single-frequency 2 μm parametric oscillator/amplifier systems followed by a ZnGeP2 downconversion stage.
We report on the first single-frequency parametric source tunable in the longwave infrared with an output energy of 1 mJ. The source is then used in a lidar to detect chemicals in the vapor phase.
Laser-induced damage threshold (LIDT) measurements were performed on blank, uncoated Rb:KTiOPO4 (RKTP) samples at 1.03 μm with pulse durations of 330 and 930 fs and a repetition rate of 100 kHz, including temperature dependence.
A laser-induced damage study is performed on blank, uncoated Rb:KTiOPO4 (RKTP) samples at 1.03 mu m with two different pulse durations of similar to 0.3 and similar to 1.0 ps and a repetition rate of 100 kHz. The effect of the sample temperature is also considered.
We report on passive mode-locking of a Ti:sapphire laser employing novel saturable absorbers based on low-dimensional carbon nanostructures such as single-walled carbon nanotubes and monolayer graphene. The mode-locked operation with both saturable absorbers were characterized and compared to pure Kerr-lens mode-locking.
We report on passive mode-locking of a Ti:sapphire laser employing a single-walled carbon nanotube saturable absorber (SWCNT-SA) specially designed and fabricated for wavelengths near 800 nm. Mode-locked pulses as short as 62 fs were generated at a repetition rate of 99.4 MHz. We achieved output powers from the SWCNT-SA mode-locked laser as high as 600 mW with a slope efficiency of 26%. The characteristics of SWCNT-SA-assisted mode-locking were compared with those of Kerr-lens mode-locking without SWCNT-SA.
We demonstrate wavelength locking of a diode laser at 760 nm with feedback from an elastic transmission grating in the Littrow configuration. The laser was in a single longitudinal mode with a side-mode suppression of 20 dB. By stretching the grating the laser could be tuned over a few nm. The grating was fabricated in a silicone elastomer ( polydimethylsiloxane) by a moulding technique, and coated by a thin layer of Ti and Au to achieve an increased diffraction efficiency needed for efficient locking.
Erbium (Er)- and Ytterbium (Yb)-codoped monoclinic KLu(WO4) 2 single crystals were grown by top seeded solution growth-slow cooling method for several different doping concentrations. Growth parameters have been optimized to obtain macrodefect-free single crystals. Er energy levels involved in the 4I13/2 → 4I 15/2 were determined by 6 K polarized optical absorption. The maximum emission cross section for this electronic transition has been evaluated, being 2.85 × 10-20 cm2 for E||Nm at 1535 nm. Laser oscillation in the 1.5 μm range was obtained by pumping the Yb ion at 980 nm and sensitizing Er. The maximum output power achieved was 152 mW, with 1.2% slope efficiency.
The fluorescence dynamics in Er3+ and Yb3+ doped KGd(WO4)(2) and KY(WO4)(2) has been investigated. Lifetimes have been measured for the Yb(F-2(5/2)), Er(I-4(13/2)), and Er(S-4(3/2)) levels around 1, 1.5, and 0.55 mu m, respectively. The Yb(F-2(5/2)) lifetimes show a decreasing trend toward the limiting Er(I-4(11/2)) lifetime with increasing Er-to-Yb concentration ratio, whereas the Er(I-4(13/2)) lifetimes are mostly unaffected by the doping concentrations. A rate equation analysis has been performed to explain the observed behavior and gain is calculated for a continuous-wave laser at 1.53 mu m to find the optimum doping concentrations for high gain.
High quality Er:Yb:KLu(WO4)2have been grown using TSSG method and spectroscopically investigated . The laser performance is compared with that in Er:Yb:KY(WO4)2. Role of upconversion processes and optimum doping concentrations have been estimated.
Here we show the results we obtained in the fabrication of planar wave guide lasers based on monoclinic double tungstates doped with Er3+ and Tm3+. We have successfully introduced these ions into the lattice matched KY0.59Gd0.19Lu0.22(WO4)(2) epitaxial layers grown on KY(WO4)(2) substrates without loss of optical quality and keeping a high refractive index contrast between the epitaxial layer and the substrate. We characterized the waveguiding properties of these epitaxial layers at lambda = 632.8 nm by dark modes spectroscopy, and we showed that these waveguides can support several TE and TM modes. Spectroscopic characterization of the active lanthanide ions in these crystals is also presented.
An overall quantum conversion efficiency of 7.8% is achieved by intracavity mixing the signal and idler of a 1.064-μm pumped Rb:PPKTP OPO in BaGa4Se7, generating >0.7 mJ pulse energy at ~7 μm and 100 Hz.
We report on a AgGaSe2 optical parametric oscillator (OPO), intracavity pumped by the 1.85-μm signal pulses of a 1.064-μm pumped Rb:PPKTP OPO. It operates at 100 Hz with idler tunability from ~8 to 18 μm.
We report on an AgGaSe2 optical parametric oscillator (OPO), intracavity pumped by the 1.85-μm signal pulses from a 1.064-μm pumped Rb:PPKTP OPO. It operates at 100 Hz with idler tunability from 5.8 to 8.3 μm.
We employ the new chalcogenide crystal BaGa2GeSe6 for the first time for frequency down-conversion into the mid-IR, in an optical parametric oscillator (OPO), intracavity pumped by the signal wave of a 1.064-μm pumped Rb:PPKTP OPO. .
An overall quantum conversion efficiency of 7.8% is achieved by intracavity mixing the signal and idler of a 1.064 mu m pumped Rb: PPKTP optical parametric oscillator in BaGa4Se7. In this way, a pulse energy of similar to 0.71 mJ is generated at similar to 7 mu m for a repetition rate of 100 Hz. Tuning of the mid-IR radiation is demonstrated by heating of the Rb: PPKTP crystal.
A 1.064 mu m pumped Rb:PPKTP optical parametric oscillator (OPO) generates mid-IR radiation by intracavity mixing the resonant signal and idler waves in AgGaSe2. The similar to 6 ns pulses at similar to 7 mu m have an energy of 670 mu J at 100 Hz, equivalent to an average power of 67 mW. The overall quantum conversion efficiency from 1.064 mu m amounts to 8%, and the power conversion efficiency is 1.2%.
A AgGaSe2 nonlinear crystal placed in a coupled cavity is intracavity pumped by the similar to 1.85-mu m signal pulses of a 1.064-mu m pumped Rb: PPKTP doubly-resonant optical parametric oscillator (OPO) operating at a repetition rate of 100 Hz. Using two samples cut for type-I and II phase-matching, the overall idler tunability of the singly-resonant AgGeSe2 OPO covers an unprecedented spectral range from 5.8 to similar to 18 mu m in the mid-IR.
We report on a AgGaSe2 optical parametric oscillator (OPO), intracavity pumped by the 1.85-μm signal pulses of a 1.064-μm pumped Rb:PPKTP OPO. It operates at 100 Hz with idler tunability from ∼8 to 18 μm.
Intracavity difference-frequency generation (DFG) between signal and idler pulses is investigated in orientation-patterned GaAs inside the cavity of a similar to 1 mu m pumped nanosecond optical parametric oscillator (OPO). Using two different samples and temperature tuning in the non-critical configuration, tunability between 7 and 9.2 mu m is demonstrated. The superior thermo-mechanical properties of OPGaAs enabled also for the first time operation of this cascaded scheme at kilohertz (1-3 kHz) repetition rates reaching average powers similar to 10 mW in the mid-IR.
We present a narrowband, non-resonant optical parametric oscillator based on 5-mm thick Rb-doped periodically-poled KTiOPO4 (PPKTP) operating in the high-energy/low repetition-rate regime. An uncoated volume Bragg grating (VBG) is employed as one of the cavity mirrors reflecting only the signal whereas the other cavity mirror is reflecting only the idler. Pumping by a Nd:YAG laser at 1.0642 mu m in a double-pass, the signal plus idler output energy reached almost 5 mJ at a repetition rate of 100 Hz corresponding to a conversion efficiency of similar to 26%. Both signal and idler are narrowband with full width at half maximum (FWHM) of 0.5 nm at 1942 nm and 0.76 nm at 2355 nm, respectively.
A Nd:YVO4 laser operating at 1064 nm generating a stable mode-locked train of 10 ps-long dark pulses with a 211 MHz repetition rate is presented. The mode-locking relies on a periodic loss modulation produced by intra-cavity sum-frequency mixing with a synchronous bright-pulse train from a mode-locked femtosecond Yb:KYW laser at 1040 nm. A modulation depth of 9050 was achieved for the dark pulses, confirmed by cross-correlation measurements. The ultrafast loss modulation injects power into the Nd:YVO4 laser cavity modes beyond the laser gain bandwidth. At proper laser cavity length, the detuning interaction of these modes with the lasing modes leads to the generation of periodic ultra-fast transients at frequencies above 1.5 THz.
We demonstrate broadband parametric amplification in GaSe crystal in noncollinear geometry. Seed pulses spanning 1.5-2.6μm are produced by cascaded χ(2) nonlinearity in a periodically poled Rb:KTP crystal. Amplified pulse bandwidths supporting 10-15fs transformlimited pulse durations at ~2μm central wavelength are achieved.
Frequency doubling has been achieved in femtosecond-laser-inscribed single-mode waveguides written in two periodically-poled potassium titanyl phosphate crystals. A conversion efficiency of 0.22 %W-1 was obtained for first-order quasi-phase matching at 980 nm and an efficiency of 0.02 %W-1 for third-order quasi-phase matching at 800 nm.
Since the early 1990's, a substantial effort has been devoted to the development of quasi-phased-matched (QPM) nonlinear devices, not only in ferroelectric oxides like LiNbO3, LiTaO3 and KTiOPO4 (KTP), but also in semiconductors as GaAs, and GaP. The technology to implement QPM structures in ferroelectric oxides has by now matured enough to satisfy the most basic frequency-conversion schemes without substantial modification of the poling procedures. Here, we present a qualitative leap in periodic poling techniques that allows us to demonstrate devices and frequency conversion schemes that were deemed unfeasible just a few years ago. Thanks to our short-pulse poling and coercive-field engineering techniques, we are able to demonstrate large aperture (5 mm) periodically poled Rb-doped KTP devices with a highly-uniform conversion efficiency over the whole aperture. These devices allow parametric conversion with energies larger than 60 mJ. Moreover, by employing our coercive-field engineering technique we fabricate highlyefficient sub-μm periodically poled devices, with periodicities as short as 500 nm, uniform over 1 mm-Thick crystals, which allow us to realize mirrorless optical parametric oscillators with counter-propagating signal and idler waves. These novel devices present unique spectral and tuning properties, superior to those of conventional OPOs. Furthermore, our techniques are compatible with KTA, a KTP isomorph with extended transparency in the mid-IR range. We demonstrate that our highly-efficient PPKTA is superior both for mid-IR and for green light generation-as a result of improved transmission properties in the visible range. Our KTP-isomorph poling techniques leading to highly-efficient QPM devices will be presented. Their optical performance and attractive damage thresholds will be discussed.
A study of polarization-switching characteristics under an applied electrical field at room temperature is presented for flux-grown KTiOPO4 and RbTiOPO4. By optimizing the experimental conditions, we determined the coercive field and the domain-switching time quantitatively by direct observation of the switching current. For both isomorphs, the inverse of the polarization-switching time, 1/t(s), follows an exponential dependence on the applied field E in low-field regime, and a linear dependence on E in the high-field regime. Domain morphology of KTiOPO4 based on selective etching reveals laminar structures elongated in the b crystallographic direction. An estimation of the domain-wall velocity shows that the domain speed in the polar direction is, at least, two orders of magnitude larger than in the a-b plane. The velocity along the b direction is similar to 30 times larger than along the a axis.
A nonlinear photonic crystal with a rectangular domain lattice of 6.09x6 mu m(2) has been fabricated and characterized in flux-grown KTiOPO4. It was used to demonstrate continuous-wave and multiple beam tunable blue second harmonic generation.
We report on fabrication and characterization of a nonlinear photonic crystal with a rectangular lattice in a KTiOPO4 crystal. The structure was used to demonstrate CW tunable second harmonic generation in the blue regime.
We report on the first experimental demonstration of mirrorless optical parametric oscillation. The counter-propagating idler and signal oscillate without an external cavity in a sub-µm periodically poled KTiOPO4 crystal, reaching an efficiency of 16.5%.
Parametric interaction of counterpropagating photons has the unique property of automatically establishing distributed feedback and thus realizing novel sources of coherent and tunable radiation, such as mirrorless optical parametric oscillators. This device does not require alignment or any optical components other than the second-order nonlinear medium itself(1). Here we present the first experimental demonstration of such an oscillator, which was made feasible by quasi phase-matching in a nonlinear photonic structure with submicrometre periodicity. This type of oscillator has been extensively discussed as a theoretical possibility(1-5). It generates signal and idler waves in the near- and mid-infrared, respectively, and exhibits unique and useful spectral properties. The oscillator signal is essentially a wavelength-shifted replica of the pump spectrum, and the bandwidth of the idler is two orders of magnitude narrower than that of the pump. It also has very low output wavelength sensitivity to temperature variations.
A submicron domain grating has been created in a bulk ferroelectric. Electron-beam lithography and electric-field poling were used to fabricate the 800 nm period grating in a 0.5-mm-thick flux-grown KTiOPO4 sample. The domain structure was characterized with an atomic force microscope and was used to demonstrate electrically amplitude adjustable Bragg reflections.
1mm thick KTiOPO4 was poled with 720nm domain period by employing UVlithography, chemical patterning and electric field poling. The structure was used to demonstrate 6 and 7 order quasi-phase matched backward second harmonic generation.
1mm thick KTiOPO4 was poled with 720nm domain period by employing UV-lithography, chemical patterning and electric field poling. The structure was used to demonstrate 6 and 7 order quasi-phase matched backward second harmonic generation.
A 1 turn thick flux-grown KTiOPO4 sample was poled with a 720 nm domain period by employing deep-UV laser lithography, chemical patterning, and electric field poling. An atomic force microscope was used to characterize the periodic domain structure. The sample was used to demonstrate sixth and seventh order quasi-phase-matched backward second-harmonic generation.
We report on the progress in fabrication of sub-micrometer ferroelectric domain gratings in KTiOPO4. Periods as short as 565 nm have been created in the bulk of the crystal by electric-filed poling.
The inverse piezoelectric effect is used to produce high-resolution images of ferroelectric domains in periodically poled KTiOPO4 crystals on their nonpolar y-face using atomic force microscopy. We demonstrate that the technique is convenient for studying the nucleation and growth of domains in a periodically poled KTiOPO4 sample.
Some novel techniques to do periodic poling of KTP are described. Emphasis on ways to avoid domain broadening and merging of domains is presented with reference to the original properties of flux grown KTP. For sub-Am structures E-beam lithography and deep UV-laser lithography were used to pattern the samples, and chemical process to promote selective poling to obtain high quality domain gratings in up to 1 mm thick samples.