Rotation rate of a three-wing rotor illuminated by upward-directed focused beam in optical tweezers

The optical torque and the trapping position (focal point) in optical tweezers are analyzed for upward-directed focused laser illumination using a ray optics model, considering that laser light is incident at not only the lower surface but also the side surface of a 3-wing rotor. The viscous drag force due to the pressure and the shearing stress on all surfaces of the rotor is evaluated using computational fluid dynamics. The rotation rate is simulated in water by balancing the optical torque with the drag force, resulting in 500 rpm for an SU-8 rotor with 20 μm diameter at a laser power of 200 mW. The trapping position is estimated to be 7.6 μm in the rotor with an upward-directed laser at 200 mW via an objective lens having a numerical aperture of 1.4. Both the rotation rate and the trapping position agree well with the values obtained in the experiment.     

High-efficiency,high-repetition-rate,temperature-tuning optical parametric oscillator based on periodically poled MgO-doped lithium niobate

We report a compact and viable source of high-efficiency, high-repetition-rate, temperature-tuning, mid-IR optical parametric oscillator (OPO) based on periodically poled MgO-doped lithium niobate (PPMgOLN) pumped by a homemade high power AOM Q-switched Nd:YVO₄ laser centered at 1.064 μm. With an optimal plane-concave resonator configuration, average output power of 5.7 W at 2.73 μm was obtained when the pump power was 25 W at the repetition rate of 80 kHz. The conversion efficiency from the 1.064 μm laser to the 2.73 μm laser was 22.8%. Temperature tuning of the OPO yielded a signal wavelength range from 1.67 to 1.75 μm and an idler wavelength in the range of 2.72 to 2.92 μm.     

A compact,widely tunable intracavity PPLN optical parameter oscillator driven by an Nd:YAG/Cr:YAG composite crystal laser

Based on periodically poled lithium niobate (PPLN), a mini intracavity optical parameter oscillator (IOPO) driven by an diode-end-pumped composite Nd³⁺:YAG/Cr⁴⁺:YAG laser was demonstrated. The PPLN wafer has 20 domain reversal periods from 27.8 to 31.6 μm with a step of 0.2 μm between the neighbor periods. The output signal laser of OPO can be widely tunable in the range of 1402–1676 nm by changing the period at a certain temperature of 50°C. Under the diode pump power of 14 W, the maximum average output power of 600 mW at 1534 nm with pulse width of 2.0 ns and repetition rate of 16 kHz was obtained, corresponding to a peak power of 18.7 kW and a single pulse energy of 37.5 μJ, respectively.     

Online monitoring of ethane traces in exhaled breath with a difference frequency generation spectrometer

We report a transportable mid-infrared laser cavity leak-out spectrometer for online detection of trace gases. The laser spectrometer is based on continuous-wave difference-frequency generation in the wavelength region around 3 μm. Sensitive spectroscopic trace gas monitoring was achieved using a high-finesse ring-down cavity. For difference-frequency generation, we use a periodically poled lithium niobate (PPLN) crystal, pumped by a Nd:YAG laser (signal wave) and a diode laser (pump wave) with a tapered amplifier. A maximum power of 280 μW near λ=3.3 μm is achieved using a pump power of 180 mW at 807 nm, a signal power of 890 mW at 1064.46 nm, and a 50-mm-long PPLN crystal. The resulting system proved to be a unique tool with high sensitivity and specificity for rapid and precise breath testing. We demonstrate spectroscopic online monitoring of ethane traces in exhaled human breath with a precision of 270 parts per trillion (1σ) and a time resolution of 1 s. PACS 42.62.Be; 42.60.-v; 07.57.Ty     

Instantaneous frequency measurement using two parallel I/Q modulators based on optical power monitoring

A scheme for instantaneous frequency measurement(IFM)using two parallel I/Q modulators based on optical power monitoring is proposed.The amplitude comparison function(ACF)can be constructed to establish the relationship between the frequency of radio frequency(RF)signal and the power ratio of two optical signals output by two I/Q modulators.The frequency of RF signal can be derived by measuring the optical power of the optical signals output by two I/Q modulators.The measurement range and measurement error can be adjusted by controlling the delay amount of the electrical delay line.The feasibility of the scheme is verified,and the corresponding measurement range and measurement error of the system under different delay amounts of the electrical delay line are given.Compared with previous IFM schemes,the structure of this scheme is simple.Polarization devices,a photodetector and an electrical power meter are not used,which reduces the impact of the environmental disturbance on the system and the cost of the system.In simulation,the measurement range can reach 0 GHz-24.5 GHz by adjusting the delay amount of the electrical delay lineτ=20 ps.The measurement error of the scheme is better at low frequency,and the measurement error of low frequency 0 GHz-9.6 GHz can reach-0.1 GHz to+0.05 GHz.     

High-efficiency mid-infrared laser from synchronous optical parametric oscillation and amplification based on a single MgO:PPLN crystal

This paper presents a specially designed optical parametric oscillator (OPO) which achieved high-efficiency mid-infrared laser of 2.83 μm. The cascaded nonlinear interactions of OPO and optical parametric amplifier (OPA) were simultaneously realized in a single MgO:PPLN crystal. The signal oscillation of 1.70 μm was used to pump a secondary parametric process that resulted in amplification of the idler laser of 2.83 μm. When the MgO:PPLN crystal with a grating period of 31.2 μm was pumped by a 1.064 μm laser and operated at 148°C, the quasi-phase-matching of both OPO and OPA could be simultaneously achieved. Average output power of 7.68 W at 2.83 μm was obtained for 25 W of pump at 7 kHz. The power conversion efficiency of 2.83 μm laser was 30.7%, which was evidently higher than common OPOs.     

Heterogeneous integration of InGaAsP microdisk laser on a silicon platform using optofluidic assembly

Heterogeneous integration of InGaAsP microdisk lasers on a silicon platform is demonstrated experimentally using an optofluidic assembly technique. The 200-nm-thick, 5- and 10-μm-diameter microdisk lasers are fabricated on InP and then released from the substrates. They are reassembled on a silicon platform using lateral-field optoelectronic tweezers (LOET). The assembled laser with 5-μm diameter exhibits a threshold pump power of 340 μW at room temperature under pulse condition. The heterogeneously-integrated InGaAsP-on-Si microdisk laser could provide the much needed optical source for CMOS-based silicon photonics. The small footprint and low power consumption make them attractive for optical interconnect applications. The optofluidic assembly technique enables efficient use of the III–V epitaxial materials in silicon photonic integrated circuits.     

Yb-doped strictly all-fiber laser actively Q-switched by intermodal acousto-optic modulation

We show an actively Q-switched ytterbium-doped strictly all-fiber laser. Cavity loss modulation is achieved in a tapered optical fiber by core-to-cladding mode-coupling induced by travelling flexural acoustic waves. When the acoustical signal is switched-off, the optical power losses within the cavity are reduced, and then a laser pulse is emitted. Trains of Q-switched pulses were successfully obtained at repetition rates in the range 1–10 kHz, with pump powers between 59 and 88 mW, at the optical wavelength of 1064.1 nm. Best results were for laser pulses of 118 mW peak power, 1.8 μs of time width, with a pump power of 79 mW, at 7 kHz repetition rate.     

An application of Pb(Zr,Ti)O3 Ceramic to opto-electronic devices

A lead-zirconate-titanate ceramic is used in an electrically controllable diffraction (ECD) grating for reflection of parallel polarized light. The ECD grating used consists of a PZT ceramic with ten pairs of interdigital electrodes having 400 μm period on its surface. The characteristics of the grating and its application to an optical modulator are demonstrated experimentllly with a He−Ne 0.63 μm laser, obtaining a modulation of 60% with the applied peak voltage of 60 V at 24 kHz signal for the incident angle of 60°.     

Diode-pumped passively Q-Switched intracavity OPO with a folded cavity configuration

We present in this report an efficient KTP-based intracavity optical parametric oscillator driven by a diode-pumped Nd:GdVO₄/Cr:YAG passively Q-switched laser. For the first time, a novel folded cavity configuration was employed to set the KTP and Cr:YAG crystals separately at different fundamental beam waists. Based on the ABCD-matrix theory and by taking the thermal lens effect into account, the laser cavity was well optimized to enhance the OPO performance. A diode pump threshold as low as 1.2 W and a maximum signal (1.57 μm) average output power up to 560 mW have been achieved. Efficient energy transfer in the IOPO leads to short pulse duration (1.8–2.6 ns) and high peak power (6.8 kW) output at 1.57 μm. Additionally, the correlation dynamics between the pump laser and the OPO was analyzed in detail.     

All-solid-state cw mode-locked picosecond KTiOAsO4 (KTA) optical parametric oscillator

4 (KTA) optical parametric oscillator (OPO) synchronously pumped by a cw diode-pumped mode-locked Nd:YVO₄ oscillator–amplifier system. The laser system (pumped by 84 W of cw 808-nm diode radiation) generates 7-ps-long pulses at 1.064 μm with a repetition rate of 83.4 MHz and an average power of 29 W. The OPO, synchronously pumped by the 1.064-μm laser pulses, consists of a 15-mm-long KTA crystal (cut for type II noncritical phase-matching) in a folded signal resonant linear resonator. The average powers of the 1.54-μm signal radiation and the 3.47-μm idler radiation are 14.6 W and 6.4 W, respectively. The total OPO output of 21 W corresponds to an internal efficiency of 75%. The experimental investigations include measurements of the OPO output power (and its dependence on the pump power, the transmission of the output coupler, and the resonator length) and of the pulse properties (such as pulse duration and spectral width). The measured results are in good agreement with the predictions of a numerical analysis based on a split-step Fourier method. Received: 4 May 1998     

High-power mid-infrared tunable optical parametric oscillator based on 3-mm-thick PPMgCLN

The experimental results of a high-power tunable mid-IR laser are presented. The optical parametric oscillator (OPO) with a 3-mm-thick PPMgCLN crystal was pumped by a 1.064 μm pulse laser. When the pump power of the 1.064 μm laser was 151 W at 10 kHz, and the operating temperature of the PPMgCLN with 5% MgO doping was 100°C, average output power of 23.7 W at 3.91 μm was obtained with a slope efficiency of 18.2% for the idler resonant OPO. The variation of the 3.91 μm output power was about ±4% in 10 min continuous operation. The beam quality factor M ² was less than 2.6. The average output power of 27.4 W at 3.91 μm was also obtained with 151 W pump power and the slope efficiency of 20.9% for the signal resonant OPO by changing the coating parameters of the OPO cavity mirrors. The mid-IR wavelength tunability of 3.7–4.0 μm can be achieved by adjusting the temperature of a 29 μm period PPMgCLN crystal from 200 to 30°C.     

126-W all-fiberized single-mode laser from an 11-μm small-core fiber

We demonstrate a 126-W all-fiberized single-mode laser from an 11-μm small-core fiber. The active fiber is a strictly single-mode fiber that produces pure single-mode. The optical to optical efficiency of the fiber laser is 68.2% with ASE suppressed by a factor of ∼35 dB and no power-roll. The output power is only limited by the available pump source, scaling the pump power may achieve much higher output power using the 11 μm small-core fiber.     

Ytterbium doped all-fiber-path all-normal dispersion mode-locked laser based on semiconductor saturable mirror

In this paper, we describe a compact all-fiber-path picosecond pulse based on Ytterbium doped fiber oscillator. A home-made novel SESAM mounted on fiber is reported, by which stable mode locking is obtained. The SESAM possesses the low saturation flux 20 μJ/cm² (versus prior low saturation flux 32 μJ/cm²), which effectively reduces the pump power threshold of mode locking. The fiber laser generates 15 ps pulse trains without a dispersive delay line or anomalous dispersion in the cavity. Mode locking pulse with 30 MHz basic repetition-rate was produced, with 10–30 mW scale average output power at 1064 nm. Through 60 h of uninterrupted laser operating, mode locking is steady as ever.     

A 9.5-W 82-MHz-repetition-rate picosecond optical parametric generator with cw diode laser injection seeding

We report on an injection-seeded 9.5-W 82-MHz-repetition-rate picosecond optical parametric generator (OPG) based on a 55 mm long crystal of periodically poled lithium niobate (PPLN) with a quasi-phase-matching (QPM) grating period of 29.75 μm. The OPG is excited by a continuously diode pumped mode-locked picosecond Nd:YVO₄ oscillator-amplifier system. The laser system generates 7 ps pulses with a repetition rate of 82.3 MHz and an average power of 24 W. Without injection-seeding the total average output power of the OPG is 8.9 W, which corresponds to an internal conversion efficiency of 50%. The wavelengths of the signal and idler waves were tuned in the range 1.57–1.64 μm and 3.03–3.3 μm, respectively, by changing the crystal temperature from 150 °C to 250 °C. Injection seeding of the OPG at 1.58 μm with 4 mW of single frequency continuous-wave radiation of a distributed-feedback (DFB) diode laser increases the OPG output to 9.5 W (53% conversion efficiency). The injection seeding increases the pulse duration and reduces the spectral bandwidth. When pumped by 10 W of 1.06 μm laser radiation, the duration of the signal pulses increased from 3.6 ps to 5.5 ps while the spectral bandwidth is reduced from 4.5 nm to 0.85 nm. Seeding thus improved the time-bandwidth product from 1.98 to a value of 0.56, much closer to the Fourier limit. Received: 29 April 2002 / Published online: 8 August 2002     

Amplification assisted optical parametric oscillator in the mid-infrared region

We demonstrate a high efficiency mid-infrared laser source based on optical parametric oscillator (OPO) assisted by an intracavity optical parametric amplification (OPA). The OPA-assisted-OPO scheme was realized in one piece of commensurable dual-periodic superlattice in which the signal light generated from the OPO process serves as the pump light for the OPA process. A maximum output power of 508 mW at 3.92 μm was achieved under a pump power of 2.85 W at 1.064 μm. The pump-to-idler conversion efficiency is 17.8% and the slope efficiency is 23.8%, and the enhancements of them are 58.9% and 67.6%, respectively, comparing with the standard OPO scheme.     

8.30 μm singly resonant ZnGeP2 optical parametric oscillators pumped by a Tm,Ho:GdVO4 laser

A single resonator 8.30 μm ZnGeP₂ (ZGP) optical parametric oscillators (OPO) was reported in the paper. The OPO was pumped by a 10.2-W Tm,Ho:GdVO₄ laser at 8 kHz in a Q-switch mode, a 170-mW idler was obtained at 8.30 μm, and the output power of the idler and signal wave was 1.0 W, corresponding to an optical-optical conversion efficiency of 10.3% and a slope efficiency of 20.9%. Tm,Ho:GdVO₄ laser was pumped by a 30-W fiber-coupled laser diode (LD) at the center wavelength of 801 nm. The output wavelength of Tm,Ho:GdVO₄ laser was at 2.05 μm, and the energy per pulse of 1.28 mJ in 18 ns was achieved at 8 kHz with the peak power of 71.1 kW.     

Small-scale high-repetition-rate passively Q-switched intracavity OPO at 1.57 μm

A compact small-scale intracavity optical parametric oscillator (IOPO) at 1.57 μm, driven by a diode pumped Nd:YVO₄/Cr:YAG passively Q-switched laser, is experimentally presented. By optimizing the mode matching, low threshold (0.66 W) and high repetition rate (21 kHz) operation of the IOPO has been investigated. At the incident diode pump power of 1.56 W, the miniature (56 mm long) IOPO produces a signal average output power up to 86 mW. Efficient parametric conversion leads to short duration (1.8 ns) pulses and high peak power output (2.3 kW) at 1.57 μm. Moreover, near diffraction limited and Gaussian type signal beam profile is also observed.     

Efficient, single frequency, high repetition rate, PPLN OPO pumped by a prelase Q-switched diode-pumped Nd:YAG laser

Single axial mode operation (<200 MHz optical bandwidth) of a high repetition rate periodically poled lithium niobate optical parametric oscillator (OPO) has been obtained at signal wavelengths between 1.46 μm and 1.64 μm. OPO signal slope efficiencies of 35% have been measured for repetition rates of 5–20 kHz. Single mode operation required spectral narrowing of both the pump laser and the OPO. A simple technique of prelase Q-switching was implemented to reduce the optical bandwidth of the cw diode-pumped Nd:YAG pump laser to <1 GHz. A single intracavity étalon was then sufficient to ensure single frequency oscillation of the OPO signal. The OPO output was stable with a smooth spatial profile and an M ² value of 1.3. Received: 29 September 1999 / Published online: 27 January 2000     

Similarity of plasma conditions of some Ne-like X-ray lasers and their partner Ni-like X-ray lasers

New pump and signal laser sources for difference frequency generation (DFG) at 4 m are described. A laser diode with a 980 nm fiber Bragg grating and a 785 nm Fabry-Perot (FP) laser diode were coupled into an optical fiber and mixed in a periodically poled Mg-doped lithium niobate (PPMgLN ) crystal, resulting in efficient mid-IR DFG. The DFG power was measured to be 0.23 W for a pump power of 5 mW and a signal power of 50 mW with a slope efficiency of 0.92 mW/W². A Doppler-broadened absorption spectrum of N₂O at 2485.2 cm^-1 (3.927 m) was observed in a 0.1 m-long gas cell at a pressure of 133 Pa. The spectral linewidth of the DFG source was estimated to be 161 MHz (FWHM) for an averaging time of 700 ms. Real-time monitoring of N₂O in a multipass cell with an optical path length of 36 m at a concentration level of 1 ppm was demonstrated. PACS 42.62.Fi; 42.72.Ai; 07.57.Hm