Generation of tunable, narrow-band mid-infrared radiation through a 532-nm-pumped KTP optical parametric amplifier

We report generation of broadly tunable (2.5-4 μm), narrow-band (0.04-0.35 cm-1) pulsed infrared radiation through a nanosecond optical parametric amplifier based on potassium titanyl phosphate (KTP) pumped by the second harmonic of a 10-Hz Nd:YAG laser. Input radiation at signal wavelengths of 615-662 nm was derived from a pulsed tunable dye laser system. Advantages of this device are simplicity, the broad range of infrared wavelengths to which a single dye in the dye laser provides access, and conversion efficiencies >10% at modest levels (<150 μJ) of input radiation.     

Comparison study of CsLiB6O10 and beta-BaB2O4 as nonlinear media for optical parametric oscillators

We compare the relative merits of the new nonlinear materials CsLiB6O10 and beta-BaB2O4 for use as gain media in a singly or doubly resonant pulsed optical parametric oscillator pumped by a Q-switched Nd:YAG laser with various parameters. Angle tuning or a wide range can be theoretically stimulated under type I and type II(1) critical phase matching for CsLiB6O10 crystal. The tunable range is 237-2775 nm; the range was extended to the ultraviolet wavelength by fifth-harmonic generation in CsLiB6O10. A comparison of the tunable ranges, resonant thresholds, and conversion efficiencies of CsLiB6O10 and beta-BaB2O4 is obtained by computer simulation. We verify that CsLiB6O10 is an excellent ultraviolet crystal.     

Infrared-ultraviolet sum-frequency generation spectrometer with a wide tunability of the ultraviolet probe

We have constructed a multiplex infrared-ultraviolet (IR-UV) sum-frequency generation (SFG) spectrometer that has a wide tunable range (235-390 nm) of the UV probe wavelength. The tunable UV probe was obtained by doubling the signal output of an optical parametric amplifier pumped by a 400 nm picosecond pulse. A prism monochromator was used as a tunable sharp-cut bandpass filter to reduce stray light due to the scattering of the UV probe so that any wavelength within the tunable range can be chosen as that of the UV probe. The SFG spectra of p-mercaptobenzoic acid on a gold substrate was measured with 289 and 334 nm UV probes. The SFG vibrational band intensities due to the carbonyl stretch mode and a phenyl ring stretch mode measured with the 289 nm probe were approximately three times larger than those measured with the 334 nm probe. The enhancement was ascribed to an electronic resonant effect.     

Nd:YAG-pumped periodically poled LiNbO3 optical parametric generator seeded with the narrowband output of a 532-nm pumped optical parametric generator

We present a simple scheme to generate a continuously tunable pulsed narrow-bandwidth infrared wave. An Nd:YAG-pumped periodically poled lithium niobate optical parametric generator (OPG) is seeded with the output of another OPG pumped by the second harmonic (0.532 microm) of the Nd:YAG laser. A tunable idler wave from the 0.532-microm pumped OPG, operated away from the degenerate point, provides a narrow linewidth seed source for the 1.064-microm pumped broadband OPG. Seeding forces the second OPG to operate in a narrowband operation comparable with that of the seed source. Linewidth of the YAG-pumped OPG is 5-25 nm, in the tuning range of 1.61-1.83 microm (signal), narrowed to 1.48-1.05 nm. Methods of further reduction of linewidth also have been discussed.     

Tunable green laser source based on frequency mixing of pump and laser radiation from a Nd:YVO4 crystal operating at 1342 nm with an intracavity KTP crystal

We report on cw tunable green laser light generation from a Nd:YVO4 laser operating at 1342 nm. Visible radiation was produced by a frequency mixing of pump and laser radiation inside an intracavity KTP crystal. When Nd:YVO4 was diode pumped, green laser was tunable from 503 to 505 nm. The green tuning range increases up to 22 nm when a Ti:sapphire laser is used as the pump source. In nonoptimal conditions, and for a pump power of 650 mW, green power was above 3 mW and close to 0.1 mW for Ti:sapphire and diode pumping, respectively.     

Generation and optical parametric amplification of picosecond supercontinuum

We have demonstrated the output characteristics of optical parametric amplification (OPA) seeded by a supercontinuum (SC) generated in deionized water excited by 1064 nm. The SC spectrum (from 426 to 943 nm) overlaps well with the tuning range of a 355 nm pumped OPA for both the signal and idler. The tunable range covers from 430 to 2035 nm, with a maximum overall energy conversion efficiency of 32% in the OPA stage. A FWHM bandwidth of 54 nm near the degeneracy point from 658 to 760 nm can be generated by using a collinear OPA. Chirping of the SC pulses is also investigated with the OPA technique. The time delay between the 430 nm component and the 567 nm component of the generated SC due to chirp is measured to be -10.72 ps, increasing almost linearly with the wavelength.     

Operation of a Ti:sapphire laser pumped by a 499-nm green laser

We report, for the first time, to our knowledge, the operation of a tunable Ti:sapphire laser pumped by a third-order Raman XeCl-H(2) laser system at 499 nm with a 60-ns pulse duration. The slope efficiency is 59% for this laser, producing pulses of 20-ns duration. The highest conversion-energy efficiency obtained is 41%, with an output energy of 1.2 mJ. The tuning range for a single set of cavity mirrors is 680-834 nm and is limited mainly by the mirror reflectivity. This study shows that a combined laser system based on a XeCl excimer laser can offer wavelength diversity.     

一种适于高可靠环境的可信网络构建方法

为了保证网络接入终端的可信性和网络安全,结合可信网络连接技术以及高可用(HA)集群思想,提出了一种适于高可靠环境的可信网络构建方法。该方法在终端接入网络时,会根据平台身份是否合法,软件版本是否符合标准,是否接入了非法外设,以及网络端口的状态等安全属性进行可信准入判定,同时服务器端和客户端采用双冗余热备方式,提高系统的可靠性。实验测试表明,该方法能够成功实现服务的可信切换和终端的可信接入控制。     

Donor-based single electron pumps with tunable donor binding energy

We report on single electron pumping via a tunable number of individual donors. We use a device that essentially consists of a silicon nanowire with local arsenic implantation between a set of fine gates. A temperature-dependent characterization of the pumped current allows us to extract the ionization energy of a single arsenic donor. We observe the ionization energy to be tunable by the gate electric field over a large range of energies.     

Tunable, oblique incidence resonant grating filter for telecommunications

We have designed a tunable, oblique-incidence resonant grating filter that covers the C band as an add-drop device for incident TE-polarized light. We tune the filter by tilting a microelectromechanical systems platform onto which the filter is attached. The fabrication tolerances as well as the role of finite incident-beam size and limited device size were addressed. The maximum achievable efficiency of a finite-area device as well as a scaling law that relates the resonance peak width and the minimum device size is derived. In good agreement with simulations, measurements indicate a negligible change in shape of the resonance peak from 1526 nm at a 45 degrees angle of incidence to 1573 nm at a 53 degrees angle with a full width at half-maximum of 0.4 nm. In this range the shift of the peak wavelength is linear with respect to changes in the angle of incidence.     

All solid-state Cr:LiSAF laser

Many kinds of experiments about all solid-state Cr:LiSAF lasers have been reported. A tunable all solid-state cw laser having tunability over more than 100 nm was developed by using the spectrum selection self-injection locking (SSSIL) method in 1992. The authors realize tunable picosecond radiation from an all solid-state laser with 146-200 ps pulses in an 88 nm range. Also, 70 fs pulse generation was achieved using a Kerr-lens mode-locking pumped with an Ar⁺ laser     

Noncollinear optical parametric amplification in potassium titanyl phosphate pumped at 800 nm

The generation of broadband tunable optical pulses is demonstrated in the range of 1050-1300 nm with noncollinear optical parametric amplification of white-light seed pulses in potassium titanyl phosphate (KTiOPO(4)). Pulse bandwidths of 50 nm (12 THz) are demonstrated with pulse energies up to 20 microJ when pumped with 500 microJ, 150 fs pulses centered at 802 nm. The required signal-pump angles range from 1.9 to 5.0 degrees. The pulse duration was 60 fs after compression.     

Broad Tunable Two-photon-resonant Parametric Oscillators for Vacuum Ultraviolet

Abstract

We derive the condition for broad tunability of optical parametric oscillators (OPOs) based on two-photon-resonant four-wave mixing in media with a centre of inversion. Our theory takes into account both depletion of the pump due to two-photon absorption (TPA) and the effect of population saturation. We show that to achieve a broad tunable range in a four-wave two-photon resonant OPO, it is necessary to provide significant TPA of the pump over the length of the nonlinear medium without any intermediate resonances. We make estimates for OPOs based on electronic transitions in rare gases, organic solutions, and glasses with wide transparent bands, and show that such media may be very promising for constructing broadly tunable coherent sources. In particular, we demonstrate the feasibility of constructing an OPO using neon pumped by an argon excimer laser with a tuning range from 70 nm to 1000 nm spanning the vacuum ultraviolet, visible and infrared regions.     

Three- and four-photon absorption of a multiphoton absorbing fluorescent probe

High-order multiphoton excitation processes are becoming a reality for fluorescence imaging and phototherapy treatment because they afford minimization of scattered light losses and a reduction of unwanted linear absorption in the living organism transparency window, making them less susceptible to photodamage, while improving the irradiation penetration depth and spatial resolution. We report the four-photon-excited fluorescence emission of (7-benzothiazol-2-yl-9,-didecylfluoren-2-yl)diphenylamine in hexane and its four-photon absorption cross section sigma4' = 8.1 x 10(-109) cm8 s3 photon(-3) for the transition S0 --> S1 when excited at 1600 nm with a tunable optical parametric generator (OPG) pumped by picosecond laser pulses. When pumped at 1200 nm, three-photon absorption was observed, corresponding to the same transition.     

Solid hydrogen Raman shifter for the mid-infrared range (4.4-8 microm)

We developed a pulsed, continuously tunable laboratory laser source for the mid-infrared spectral range of 4.4-8 microm, which is characterized by the spectral linewidth of 0.4 cm(-1). The device is based on the stimulated backward Raman scattering in solid para-hydrogen at T = 4 K. It is pumped by a focused beam obtained from a commercial near-infrared optical parametric oscillator with output energy of approximately 20 mJ (7-ns pulse). Output energies range from 1.7 mJ at 4.4 microm to 120 microJ at 8 microm, which correspond to quantum efficiencies of 0.53 and 0.08, respectively. Spectra of NO, H2O, and CH4 molecules in the mid-infrared were recorded. The operation of the Raman cell pumped with 532-nm radiation was also studied.     

Kilohertz femtosecond UV-pumped visible beta-barium borate and lithium triborate optical parametric generator and amplifier

We demonstrate optical parametric generation and amplification of femtosecond pulses in the entire visible range using type-I phase-matched beta-barium borate and lithium triborate crystals pumped by the frequency-doubled output of a Ti:sapphire regenerative amplifier at 395 nm. The output is tunable from 470 to 770 nm with a pulse width of ~170 fs at a repetition rate of 1 kHz and a maximum output energy of ~1.1 muJ/pulse. The visible optical parametric amplifier output was then frequency doubled and sum frequency mixed with the fundamental output of Ti:sapphire at 790 nm to produce UV pulses with a conversion efficiency of greater than 25%. The second harmonic generated UV pulses are tunable from 240 to 380 nm with a maximum pulse energy of ~260 nJ/pulse.     

Tunable high-power narrow-spectrum external-cavity diode laser at 675 nm as a pump source for UV generation

High-power narrow-spectrum diode laser systems based on tapered gain media in an external cavity are demonstrated at 675 nm. Two 2 mm long amplifiers are used, one with a 500 μm long ridge-waveguide section (device A), the other with a 750 μm long ridge-waveguide section (device B). Laser system A based on device A is tunable from 663 to 684 nm with output power higher than 0.55 W in the tuning range; as high as 1.25 W output power is obtained at 675.34 nm. The emission spectral bandwidth is less than 0.05 nm throughout the tuning range, and the beam quality factor M(2) is 2.07 at an output power of 1.0 W. Laser system B based on device B is tunable from 666 to 685 nm. As high as 1.05 W output power is obtained around 675.67 nm. The emission spectral bandwidth is less than 0.07 nm throughout the tuning range, and the beam quality factor M(2) is 1.13 at an output power of 0.93 W. Laser system B is used as a pump source for the generation of 337.6 nm UV light by single-pass frequency doubling in a bismuth triborate (BIBO) crystal. An output power of 109 μW UV light, corresponding to a conversion efficiency of 0.026% W(-1), is attained.     

Absorption spectra of dye solutions measured using a white light thermal lens spectrophotometer

We describe a two-beam thermal lens spectrophotometer that uses a xenon lamp as the excitation source and a low power diode pumped Nd-YAG laser as the probe light. The white light from the xenon source is filtered using a variable interference filter producing a partial monochromatic light within the spectral range 400-700 nm and with a spectral resolution of 10 nm. We measure the thermal lens spectrum of a nonfluorescent dye (Malachite Green) and show that this spectrum reproduces its absorbance spectra measured by the usual transmission method. A comparison of the thermal lens and the absorbance spectra of a fluorescent dye (Rhodamine B) reveals substantial differences. These differences can yield important applications of the device for the characterization of fluorescent materials.     

Highly efficient, widely tunable, 10-Hz parametric amplifier pumped by frequency-doubled femtosecond Ti:sapphire laser pulses

We report a 10-Hz, highly efficient, widely tunable (from the visible to the IR), broadband femtosecond optical parametric generator and optical parametric amplifier (OPA) in BBO, LBO, and CBO crystals pumped by the frequency-doubled output of a regeneratively amplified Ti:sapphire laser at 400 nm. The output of the system is continuously tunable from 440 nm to 2.5 mum with a maximum overall efficiency of ~25% at 670 nm and an optical conversion efficiency of more than 36% in the OPA stage. The effects of the seed beam energy, the type of the crystal and the crystal length, and the pumping energy of the output of the OPA, such as the optical efficiency, the bandwidth, the pulse duration, and the group velocity mismatch between the signal and the idler and between the seeder and the pump, are investigated. The results provide useful information for optimization of the design of the system.     

All-solid-state tunable DCM dye laser pumped by a diode-pumped Nd:YAG laser

Lasing is observed near 620 nm in a DCM dye doped TiO(2)-content organically modified silicate (ORMOSIL) pumped by frequency-doubled radiation from a diode-pumped Q-switched Nd:YAG laser. The laser wavelength is tunable over 60 nm. A conversion efficiency of 18% is obtained at its central wavelength of 621 nm. The laser output energy has only a 10% reduction after 27,000 pulses at a pump repetition rate of 30 Hz and a pump intensity of 1 J/cm(2). An all-solid-state, compact, long-lifetime, and tunable dye laser has been demonstrated.