Efficient femtosecond optical parametric generation in group-velocity-matched MgO:PPLN at 10†MHz.

We report on efficient single-pass optical parametric generation (OPG) of broadband femtosecond pulses in the mid-infrared at 10 MHz by exploiting group-velocity-matched interaction in a 42-mm-long MgO:PPLN crystal. Using a microchip-started femtosecond amplified Mamyshev oscillator at 1064 nm as the pump, the OPG source can provide tunable femtosecond pulses across 1516-1566 nm in the signal and 3318-3568 nm in the idler, with slope efficiencies of ∼93% and ∼41%, respectively. For 650 mW of average input pump power, signal powers of up to 283 mW at 1524 nm are generated, with more than 200 mW over the entire tuning range. Idler average powers of up to 104 mW at 3450 nm, with more than 80 mW across the full range, are also obtained. For input pump pulses of ∼182 fs, the generated signal pulses have a duration of ∼460 fs at 1516 nm. The idler pulses have a typical bandwidth of ≥100 nm over the entire tuning range, and as wide as 181 nm at 3457 nm. The OPG source exhibits excellent passive power stability, better than 0.5% rms in the signal and 0.6% rms in the idler, over 1 h, both in Gaussian TEM00 spatial profile with M2 < 1.5.

Tunable vortex beam generation using an optical parametric oscillator with an antiresonant-ring interferometer.

We report a high-average-power picosecond optical vortex source tunable in the near-infrared, using an antiresonant-ring (ARR) interferometer internal to an optical parametric oscillator (OPO) in combination with an external cylindrical lens for astigmatic mode conversion. The ARR OPO is tunable in the signal across 1457-1647 nm with a vortex intensity profile and up to 1 W of average power at 1602 nm. The corresponding idler is tunable over 3006-3945 nm in a Gaussian intensity profile with as much as 1.6 W at 3168 nm. The vortex signal and the Gaussian idler exhibit passive power stability better than 1.7% rms and 1.3% rms, respectively, over >1h. The signal pulses have a Gaussian duration of <19ps with a time-bandwidth product of ΔτΔν<3.6 across the tuning range.

Green-pumped continuous-wave parametric oscillator based on fanout-grating MgO:PPLN.

We report the first green-pumped continuous-wave (cw) optical parametric oscillator (OPO) based on MgO:PPLN in a fanout grating design. Pumped by a single-frequency cw laser at 532 nm, the OPO provides tunable radiation across 813-1032 nm in the signal and 1098-1539 nm in the idler by simple mechanical translation at a fixed temperature of 55°C. By deploying a 25-mm-long crystal to minimize thermal effects and using output coupling for the signal wave, we generate a total output power of up to 714 mW at 30% extraction efficiency in excellent Gaussian beam quality with M2<1.1 and high output stability. Simultaneous measurements of signal and idler power result in passive stability of 2.8% and 1.8% rms, respectively, over 1 h. Strong thermal effects contribute to the high stability and excellent beam quality, while linear and green-induced infrared absorption limit the power scaling capabilities of the OPO. The output signal is single-mode with an instantaneous linewidth of ∼3MHz and frequency stability of ∼84MHz over 72 s.

Multi-structured-beam optical parametric oscillator.

Structured beams, conventionally generated through the spatial mode conversion of the Gaussian laser beams, have attracted great interest in recent years. Optical parametric oscillators (OPOs) have demonstrated the potential for the generation of tunable structured beams directly from an input pump source. However, to date, a particular OPO design has been shown to produce such beams only in a specific configuration and different spatial structured beams require different system architectures. Here, we report the generation of multiple-structured beams from a single OPO device. Using a vortex-beam-pumped ultrafast OPO in singly-resonant oscillator design and through the control of the mode structure of the resonant beam using a simple intracavity aperture, we generate vortex, Airy, vortex Airy, and Gaussian signal beams over a tunable wavelength range across 1457-1680 nm, simultaneous with vortex beam in the non-resonant idler across 2902-3945 nm, from different ports of the device. The signal and idler vortices have output power in excess of 1 W and maximum vortex order of li=2, while the Airy beam and vortex Airy beam have output power of more than 200 mW. The generic experimental design can be used to provide multi-structured spatial beams with broad tunability across different spectral regions by proper selection of pump laser and nonlinear material and in all times-scales from continuous-wave to ultrafast femtosecond domain.

Yb-fiber-pumped, high-beam-quality, idler-resonant mid-infrared picosecond optical parametric oscillator.

We report an Yb-fiber-pumped picosecond optical parametric oscillator (OPO) delivering high average power in excellent beam quality throughout the mid-infrared (mid-IR). Using MgO:PPLN as the nonlinear crystal and configured as a singly-resonant oscillator in the mid-IR idler wave, the OPO provides up to 3.5 W average power in high spatial quality with M2<1.8 across a continuous tuning range of 4028-2198 nm, with M2<1.5 at 4000 nm. It can also deliver as much as 4.3 W of signal power in an output beam with M2<1.4 across 1446-2062 nm. The extracted idler exhibits a passive power stability better than 0.46% rms over 1 hour across the entire mid-IR tuning range. We have also investigated OPO cavity length detuning behavior about the zero-group-velocity-mismatch crossing point and its effects on output power.

Tunable vector-vortex beam optical parametric oscillator.

Vector-vortex beams, having both phase and polarization singularities, are of great interest for a variety of applications. Generally, such beams are produced through systematic control of phase and polarization of the laser beam, typically external to the source. However, efforts have been made to generate vector-vortex beams directly from the laser source. Given the operation of the laser at discrete wavelengths, vector-vortices are generated with limited or no wavelength tunability. Here, we report an experimental scheme for the direct generation of vector-vortex beams. Exploiting the orbital angular momentum conservation and the broad wavelength versatility of an optical parametric oscillator, we systematically control the polarization of the resonant beam using a pair of intracavity quarter-wave plates to generate coherent vector-vortex beam tunable across 964-990 nm, with output states represented on the higher-order Poincaré sphere. The generic experimental scheme paves the way for new sources of structured beams in any wavelength range across the optical spectrum and in all time-scales from continuous-wave to ultrafast regime.

Singly-resonant pulsed optical parametric oscillator based on orientation-patterned gallium phosphide.

We report a pulsed singly-resonant optical parametric oscillator (OPO) based on the new nonlinear crystal, orientation-patterned gallium phosphide (OP-GaP). Pumped by a Q-switched Nd:YAG laser at 1064 nm, and using a 40-mm-long OP-GaP crystal with a single grating period of Λ=16 µm, the OPO generates signal and idler output across 1.6-1.7 µm and 2.8-3.1 µm, respectively, under temperature tuning. For an average pump power of 4.8 W at 50 kHz pulse repetition rate, mid-infrared idler powers of up to ∼20 mW have been obtained at 2966 nm with high output stability. For pump pulses of ∼13 ns duration, the OPO generates ∼6 ns output signal pulses. From temperature-dependent wavelength tuning measurements at two different pump powers of 4.2 W and 1.2 W, a discrepancy of 11-17°C in the internal crystal temperature is estimated, implying that the OP-GaP sample suffers from increasing thermal effects at higher pump powers due to absorption.

Critically phase-matched Ti:sapphire-laser-pumped deep-infrared femtosecond optical parametric oscillator based on CdSiP2.

We report a high-repetition-rate femtosecond optical parametric oscillator (OPO) for the deep-infrared (deep-IR) based on type-I critical phase-matching in CdSiP2 (CSP), pumped directly by a Ti:sapphire laser. Using angle-tuning in the CSP crystal, the OPO can be continuously tuned across 7306-8329 nm (1201-1369 cm-1) in the deep-IR. It delivers up to 18 mW of idler average power at 7306 nm and >7 mW beyond 8000 nm at 80.5 MHz repetition rate, with the spectra exhibiting bandwidths of >150 nm across the tuning range. Moreover, the signal is tunable across 1128-1150 nm in the near-infrared, providing up to 35 mW of average power in ∼266 fs pulses at 1150 nm. Both beams exhibit single-peak Gaussian distribution in TEM00 spatial profile. With an equivalent spectral brightness of ∼5.6×1020photons s-1 mm-2 sr-10.1% BW-1, this OPO represents a viable alternative to synchrotron and supercontinuum sources for deep-IR applications in spectroscopy, metrology, and medical diagnostics.

Picosecond difference-frequency-generation in orientation-patterned gallium phosphide.

We report the generation of tunable high-repetition-rate picosecond radiation in the mid-infrared using the new quasi-phase-matched nonlinear material of orientation-patterned gallium phosphide (OP-GaP). The source is realized by single-pass difference-frequency-generation (DFG) between the output signal of a picosecond optical parametric oscillator (OPO) tunable across 1609-1637 nm with input pump pulses at 1064 nm in OP-GaP, resulting in tunable radiation across 3040-3132 nm. Using a 40-mm-long crystal, we have generated up to 57 mW of DFG average power at ~80 MHz repetition rate for a pump power of 5 W and signal power of 0.9 W, with >30 mW over >50% of the tuning range. The DFG source exhibits a passive power stability better than 3.2% rms over 1 hour in good spatial beam quality. To the best of our knowledge, this is the first picosecond frequency conversion source based on OP-GaP.

Ultrafast Airy beam optical parametric oscillator.

We report on the first realization of an ultrafast Airy beam optical parametric oscillator (OPO). By introducing intracavity cubic phase modulation to the resonant Gaussian signal in a synchronously-pumped singly-resonant OPO cavity and its subsequent Fourier transformation, we have generated 2-dimensional Airy beam in the output signal across a 250 nm tuning range in the near-infrared. The generated Airy beam can be tuned continuously from 1477 to 1727 nm, providing an average power of as much as 306 mW at 1632 nm in pulses of ~23 ps duration with a spectral bandwidth of 1.7 nm.

High-power, high-repetition-rate performance characteristics of ß-BaB2O4 for single-pass picosecond ultraviolet generation at 266 nm.

We report a systematic study on the performance characteristics of a high-power, high-repetition-rate, picosecond ultraviolet (UV) source at 266 nm based on ß-BaB2O4 (BBO). The source, based on single-pass fourth harmonic generation (FHG) of a compact Yb-fiber laser in a two-crystal spatial walk-off compensation scheme, generates up to 2.9 W of average power at 266 nm at a pulse repetition rate of ~80 MHz with a single-pass FHG efficiency of 35% from the green to UV. Detrimental issues such as thermal effects have been studied and confirmed by performing relevant measurements. Angular and temperature acceptance bandwidths in BBO for FHG to 266 nm are experimentally determined, indicating that the effective interaction length is limited by spatial walk-off and thermal gradients under high-power operation. The origin of dynamic color center formation due to two-photon absorption in BBO is investigated by measurements of intensity-dependent transmission at 266 nm. Using a suitable theoretical model, two-photon absorption coefficients as well as the color center densities have been estimated at different temperatures. The measurements show that the two-photon absorption coefficient in BBO at 266 nm is ~3.5 times lower at 200°C compared to that at room temperature. The long-term power stability as well as beam pointing stability is analyzed at different output power levels and focusing conditions. Using cylindrical optics, we have circularized the generated elliptic UV beam to a circularity of >90%. To our knowledge, this is the first time such high average powers and temperature-dependent two-photon absorption measurements at 266 nm are reported at repetition rates as high as ~80 MHz.

Yb-fiber-laser-pumped, high-repetition-rate picosecond optical parametric oscillator tunable in the ultraviolet.

We report a compact tunable 240-MHz picosecond source for the ultraviolet based on intra-cavity frequency doubling of a signal-resonant MgO:sPPLT optical parametric oscillator (OPO), synchronously pumped at 532 nm in the green by the second harmonic of a mode-locked Yb-fiber laser at 80-MHz repetition rate. By deploying a 30-mm-long multi-grating MgO:sPPLT crystal for the OPO and a 5-mm-long BiB(3)O(6) crystal for internal doubling, we have generated tunable UV radiation across 317-340.5 nm, with up to 30 mW at 334.5 nm. The OPO also provides tunable visible signal in the red, across 634-681 nm, and mid-infrared idler radiation over 2429-3298 nm, with as maximum signal power of 800 mW at 642 nm. The signal pulses have a temporal duration of 12 ps at 665 nm and exhibit high spatial beam quality with Gaussian profile. The signal power is recorded to be naturally stable with a fluctuation of 1.4% rms over 14 hours, while UV power degradation has been observed and studied.

Fiber-laser-pumped, dual-wavelength, picosecond optical parametric oscillator.

We report a simple, compact, picosecond, dual-wavelength optical parametric oscillator (DW-OPO) at 160 MHz, based on two MgO:PPLN crystals sharing the same cavity and synchronously pumped by an Yb-fiber laser at 1064 nm. The two signal and idler wavelength pairs are independently tunable in the near- and mid-infrared across 1550-1615 nm and 3118-3393 nm, respectively, and can be arbitrarily tuned, even to degeneracy and beyond, without coherent coupling, irrespective of operating wavelength. The DW-OPO provides two signal and idler pulse trains and delivers as much as 1.5 W of average signal power at a degenerate wavelength of 1550 nm from each arm, at a total (signal plus idler) power extraction efficiency of as much as 44%. The two output signal pulse trains have durations of ∼18 ps and ∼15.2 ps, with Gaussian spatial quality, and exhibit passive power stability, better than 3.6% rms over >5 h. We also demonstrate the possibility of tailoring the pulse trains from the DW-OPO by controlling the delay between the pump pulses at the input to the two MgO:PPLN crystals.

A Prospective Real World Experience of Moxonidine Use in Indian Hypertensive Patients-Prescription beyond Current Guidelines.

OBJECTIVE: The primary objective of this study was to assess the use of moxonidine, a centrally acting anti-hypertensive agent in real world practice. MATERIAL AND METHODS: Patients who attended out-patients clinic with diagnosis of hypertension were enrolled in the study. Demographics with co-morbid illnesses of all patients were recorded. Patient's prescriptions were recorded and anti-hypertensive medications were also analysed. RESULTS: A total of 990 patients were eligible during the study period. Moxonidine was used in 4.54% of patients. Two groups could be identified in moxonidine users - one Group with resistant hypertension (30 patients, 3.03% of total, 66.66% of moxonidine users) on multiple drugs to control BP and another Group with intolerance to conventional, first line drugs (15 patients 1.51% of total, 33.33% of moxonidine users). Moxonidine was not used in newly diagnosed hypertension cases. Resistant hypertension and renal failure predicted the use of moxonidine. Majority of drug used was as per current guidelines. CONCLUSIONS: Our study results reflected real world practice of current anti-hypertensive therapy. Patients generally receive medications in accordance with current recommendations and guidelines. Small but significant proportion of patients may require use of drugs like moxonidine to control high BP. Guidelines need to incorporate these real world practices.

Stable, continuous-wave, ytterbium-fiber-based single-pass ultraviolet source using BiB3O6.

We report stable continuous-wave (CW) ultraviolet (UV) generation at 354.7 nm using single-pass sum-frequency-generation (SFG) of a CW Yb-fiber laser at 1064 nm in the nonlinear crystal, BiB3O6. The 532 nm radiation is obtained by single-pass second-harmonic generation of the Yb-fiber laser in a 30-mm-long MgO:sPPLT crystal. Using a 10-mm-long BiB3O6 crystal for SFG, with a measured angular acceptance bandwidth of 0.57 mrad, we generate as much as 68 mW of CW single-frequency UV radiation with a passive power stability better than 3.2% rms over 2 h and frequency stability better than 436 MHz over 2.5 h. The UV output beam has a TEM00 spatial profile with M(x)(2)<1.6 and M(y)(2)<1.8.

Directly phase-modulation-mode-locked doubly-resonant optical parametric oscillator.

We present results on direct mode-locking of a doubly-resonant optical parametric oscillator (DRO) using an electro-optic phase modulator with low resonant frequency of 80 MHz as the single mode-locking element. Pumped by a cw laser at 532 nm and based on MgO:sPPLT as the nonlinear material, the DRO generates 533 ps pulses at 80 MHz and 471 ps pulses at 160 MHz. Stable train of mode-locked pulses is obtained at a modulation depth of 1.83 radians when the modulation frequency is precisely tuned and the cavity length is carefully adjusted. The effects of frequency detuning, modulation depth, input laser pump power, crystal temperature and position of modulator inside the cavity, on pulse duration and repetition rate have been studied. Operating at degeneracy, under mode-locked condition, the signal-idler spectrum exhibits a bandwidth of ~31 nm, and the spectrum has been investigated for different phase-matching temperatures. Mode-locked operation has been confirmed by second-harmonic-generation of the DRO output in a ß-BaB2O4 crystal, where a 4 times enhancement in green power is observed compared to cw operation.

Tunable, continuous-wave, ultraviolet source based on intracavity sum-frequency-generation in an optical parametric oscillator using BiB3O6.

We report a continuous-wave (cw) source of tunable radiation across 333-345 nm in the ultraviolet (UV) using bismuth triborate, BiB3O6 (BIBO) as the nonlinear gain material. The source is based on internal sum-frequency-generation (SFG) in a cw singly-resonant optical parametric oscillator (OPO) pumped at 532 nm. The compact tunable source employs a 30-mm-long MgO:sPPLT crystal as the OPO gain medium and a 5-mm-long BIBO crystal for intracavity SFG of the signal and pump, providing up to 21.6 mW of UV power at 339.7 nm, with >15 mW over 64% of the SFG tuning range. The cw OPO is also tunable across 1158-1312 nm in the idler, delivering as much as 1.7 W at 1247 nm, with >1W over 65% of the tuning range. The UV output at maximum power exhibits passive power stability better than 3.4% rms and frequency stability of 193 GHz over more than one minute.

The Antihypertensive Efficacy of Chlorthalidone and Telmisartan in Indian Hypertensive Patients who were Uncontrolled with Hydrochlorothiazide and Telmisartan Combination-A Prospective and an Open Label Study.

OBJECTIVE: The primary objective of this study was to evaluate the antihypertensive efficacy of the chlorthalidone and telmisartan combination in Indian hypertensive patients who remained uncontrolled after taking the hydrochlorothiazide and telmisartan combination. METHODS: A total of 100 eligible patients were enrolled in this prospective, open label study. The patients were given telmisartan (40 mg) and chlorthalidone (12.5 mg), who had not achieved the target blood pressure (140/90 mmHg) despite taking the combination of telmisartan (40 mg) and hydrochlorothiazide (12.5 mg). The assessment was done at the end of 4 weeks and 8 weeks. RESULTS: The mean SBP and DBP after taking telmisartan (40 mg) and hydrochlorothiazide (12.5 mg) were 154.88±9.57 (range 144 to 160) mmHg and 99.37±2.78 (range 92 to 106). At the end of 4 weeks of being on telmisartan (40 mg) and chlorthalidone (12.5 mg), the mean SBP and DBP were 145.56±5.12 (range 134 to 158) mmHg and 95.14±4.27 (range 84 to 100) mmHg. Significant falls in the SBP (5.32±2.64) and DBP (4.18±2.48) were noted at the end of the 4 week therapy. They were sustained at the end of 8 weeks also. The SBP target (<140 mmHg) was achieved in 24 % patients. The DBP target (<90 mmHg) was achieved in 19% patients. The combined SBP and DBP target (<140/90 mmHg) was achieved in 15% patients. No significant clinical adverse events were reported. Similar falls in the SBP and DBP were noted in the subgroups (smokers, females, diabetics, etc). CONCLUSIONS: The hypertensive patients who do not achieve the target blood pressures on telmisartan and hydrochlorothiazide can be switched on to the telmisartan and chlorthalidone combination. This combination is effective and well tolerated.

Antiresonant ring output-coupled continuous-wave optical parametric oscillator.

We demonstrate the successful deployment of an antiresonant ring (ARR) interferometer for the attainment of optimum output coupling in a continuous-wave (cw) optical parametric oscillator (OPO). The cw OPO, configured as a singly-resonant oscillator (SRO), is based on a 50-mm-long MgO:PPLN crystal and pumped by cw Ytterbium-fiber laser at 1064 nm, with the ARR interferometer integrated into one arm of the standing-wave cavity. By fine adjustment of the ARR transmission, a continuously variable signal output coupling from 0.8% to 7.3% has been achieved, providing optimum output coupling for signal and optimum power extraction for the idler, at different input pumping levels. The experimental results are compared with theoretical calculations for conventional output-coupled cw SRO, and the study shows that by reducing the insertion loss of the ARR elements, the performance of the ARR-coupled cw SRO can be further enhanced. We also show that the use of the ARR does not lead to any degradation in the cw SRO output beam quality. The proof-of-principle demonstration confirms the effectiveness of the technique for continuous, in situ, and fine control of output coupling in cw OPOs to achieve maximum output power at any arbitrary pumping level above threshold.

Tunable, high-energy, mid-infrared, picosecond optical parametric generator based on CdSiP2.

We report a tunable, high-energy, single-pass optical parametric generator (OPG) based on the nonlinear material, cadmium silicon phosphide, CdSiP(2). The OPG is pumped by a cavity-dumped, passively mode-locked, diode-pumped Nd:YAG oscillator, providing 25 µJ pulses in 20 ps at 5 Hz. The pump energy is further boosted by a flashlamp-pumped Nd:YAG amplifier to 2.5 mJ. The OPG is temperature tunable over 1263-1286 nm (23 nm) in the signal and 6153-6731 nm (578 nm) in the idler. Using the single-pass OPG configuration, we have generated signal pulse energy as high as 636 µJ at 1283 nm, together with idler pulse energy of 33 µJ at 6234 nm, for 2.1 mJ of input pump pulse energy. The generated signal pulses have durations of 24 ps with a FWHM spectral bandwidth of 10.4 nm at central wavelength of 1276 nm. The corresponding idler spectrum has a FWHM bandwidth of 140 nm centered at 6404 nm.