Subsequent Second-harmonic Generation Research Articles

725 nm watt-level injection-locked continuous-wave Ti:sapphire laser for a mercury optical lattice clock.

We develop a watt-level 725 nm continuous-wave tunable narrow linewidth injection-locked Ti:sapphire laser. The seed laser is frequency-locked on a Fabry-Perot cavity to narrow the linewidth and stabilize the frequency. Because the wavelength of the seed laser is located at the edge of the gain profile of the Ti:sapphire crystal, it is difficult to injection-lock the Ti:sapphire laser at 725 nm. A cavity mirror, which has a long-pass-filter coating with a sharp edge, is used in the Ti:sapphire cavity to suppress mode competition from the long wavelength side. This method effectively reduces the power requirement of the seed laser at 725 nm, and the Ti:sapphire laser can be injection-locked at higher output power. As a result, a 1 W output power with a 27% slope efficiency is achieved in the injection-locked laser, and a 210 mW UV laser is obtained in a subsequent second-harmonic generation stage. To the best of our knowledge, this is the shortest wavelength for the watt-level injection-locked continuous-wave Ti:sapphire laser. This laser will be used in a mercury optical lattice clock in the future.

Quality enhancement of a 355 nm sum-frequency light generated using a quality-deteriorated fundamental beam

This work provides a comprehensive study around the effect of a quality-deteriorated fundamental beam on the quality of a 355 nm wavelength beam experimentally generated using sum-frequency mixing of a second-harmonic generation (SHG) beam and its un-depleted fundamental inside a walk-off (WO) affected BBO nonlinear crystal. A slit-variable aperture is used inside the resonator of a utilized Nd:YAG resonator to generate a wide range of Hermite–Gaussian modes for the fundamental and subsequent SHG and sum-frequency generation (SFG) beams. The M2-factor of interacting beams is simulated based on the reconstruction of the recorded intensities using a recently reported technique known as few-frame decomposition method. It is found that in the worst case, due to the WO occurring in the X-direction, the M2-factor of the SFG beam is converged to 2.5 after 2 mm of crystal length and remained constant in the remaining length when the fundamental M2-factor is set for 4.5. Based on the simulation results, it is shown that the beam quality of SFG beam along the WO direction is independent of the fundamental M2-factor. It is further realized that by changing the focusing factor up to 2.84, again M2-factor of the UV-SFG beam is not exceeded from 2.5.

Tunable continuous ultraviolet light source based on diode laser

We report on extra cavity frequency doubling lasers for 266 nm with a compact, tunable extended cavity diode laser (ECDL) at 1 064 nm. The ECDL injected into a tapered amplifier yields a power of 290 mW. In a first frequency-doubling stage, about 47-mW green light at 532 nm is generated. Subsequent second-harmonic generation (SHG) employing a BBO crystal leads to about 30 μW of ultraviolet (UV) light at 266 nm. The tunable characteristic of this UV light source is discussed. The tuning span of quasi-phase matching of doubling cavity for 532 nm with PPKTP crystal is achieved with –3.5 nm by changing the temperature of PPKTP and is achieved with –1.186 nm by adjusting angle of PPKTP.

Narrow-Bandwidth Diode-Laser-Based Ultraviolet Light Source

A compact, tunable and narrow-bandwidth laser source for ultraviolet radiation is presented. A grating stabilized diode laser at 1064 nm is frequency-stabilized to below 10 kHz by using a ultra low expansion (ULE) cavity. Injecting light of the diode laser into a tapered amplifier yields a power of 290 mW. In a first frequency-doubling stage, about 47 mW of green light at 532 nm is generated by using a periodically poled KTP crystal. Subsequent second-harmonic generation employing a BBO crystal leads to about 30 μW of ultraviolet light at 266 nm.

Pulse-shape improvement during amplification and second-harmonic generation of picosecond pulses at 531 nm

We study second-harmonic generation of picosecond pulses in bulk periodically poled lithium niobate using an all-semiconductor master oscillator-power amplifier with gain-switched seed as our fundamental source. Both during amplification and during the subsequent second-harmonic generation, the signal pulse shape improves, and the resulting pulses at 531 nm are nearly independent of the seed pump conditions. Over a wide range of repetition rates and seed settings, we obtain green pulses with a duration of less than 31 ps FWHM and a peak power of more than 5.1 W. We further investigate the influence of the fundamental's spectral dynamics on pulsed second-harmonic generation efficiency and obtain excellent agreement between our measurements and previously published theoretical treatments.

Compact coherent anti-Stokes Raman scattering microscope based on a picosecond two-color Er:fiber laser system

We present a compact coherent anti-Stokes Raman scattering microscope based on a widely tunable picosecond Er:fiber laser. Intense and bandwidth-limited 1 ps pump pulses at a center wavelength of 775 nm are generated via frequency mixing within the broadband fundamental at 1.55 microm. Narrowband Stokes pulses are obtained by frequency shifting of solitons in a highly nonlinear bulk fiber and subsequent second-harmonic generation. The tuning range from 850 nm to 1100 nm gives access to vibrational resonances between 1150 cm(-1) and 3800 cm(-1). A first imaging application in the spectral region of CH stretch vibrations is demonstrated.

Synthesis and nonlinear optical properties of TeO 2–Bi 2O 3–GeO 2 glasses

Novel TeO2–Bi2O3–GeO2 glasses possessing nonlinear optical properties were successfully synthesized by the melt-quenching method. Differential thermal analysis, X-ray diffraction, Raman scattering and UV–visible spectroscopy were complementarily applied to study the glass transition and crystallization temperature, structural, thermal and optical properties. The value of the refractive index of the glasses is approximately 2.13. The thermoelectrical poling and subsequent second-harmonic generation results are also reported.

Femtosecond two-photon photoemission at 150 kHz utilizing two noncollinear optical parametric amplifiers for measuring ultrafast electron dynamics

An improved setup for femtosecond two-photon photoemission spectroscopy (TR-2PPE) is presented. Two noncollinear optical parametric amplifiers (NOPA) were operated simultaneously at a repetition rate of 150 kHz. The frequencies of the NOPA outputs were tuned such that subsequent second harmonic generation (SHG) provided the two different ultraviolet wavelengths required for the pump and probe pulse. The width of the crosscorrelation function (CC) for pump and probe pulse was sub-30 fs (FWHM).

Development of Fluorescence-based LIDAR Technology for Biological Sensing

ABSTRACT:Results of our on-going development of biological warfare agents (BWA) detection systems based on spectral detection of ultraviolet (UV) laser induced fluorescence (LIF) are presented. A compact optical parametric oscillator (OPO) with intracavity sum-frequency mixing (SFM) to generate 293 nm UV laser irradiation was developed. The OPO/SFM device was pumped by a diode-pumped Nd:YAG laser (1064 nm), including subsequent second-harmonic generation (SHG) in an external periodically poled KTiOPO4 (PPKTP) crystal. The laser generated 1.8 ns pulses at 100 Hz with an average power of 44 mW at 532 nm. The whole system could be used to deliver approximately 30 μJ laser irradiation per pulse (100 Hz) at 293 nm. The spectral detection part of the system consists of a grating and a photomultiplier tube (PMT) array with 32 channels, which can measure fluorescence spectra in the wavelength band from 250 nm to 800 nm. The detector system was designed along with a trigger laser to enable measurement of fluorescence spectra from an individual aerosol particle of simulants for BWA upon excitation with a single nanosecond laser pulse. We demonstrate the successful detection and spectral characterization of simulants for BWA, i.e., Bacillus atrophaeus (BG), Bacillus thuringiensis (BT), and Ovalbumin (OA).

Narrow-bandwidth diode-laser-based blue and ultraviolet light source

A compact, tunable and narrow-bandwidth laser source for blue and ultraviolet radiation is presented. A grating-stabilized diode laser at 922 nm is frequency-stabilized to below 100 Hz relative to a reference resonator. Injection of the diode-laser light into a tapered amplifier yields a power of 0.5 W. In a first frequency-doubling stage, more than 200 mW of blue light at 461 nm is generated by use of a periodically poled KTP crystal. Subsequent second-harmonic generation employing a BBO crystal leads to about 1 mW of ultraviolet light at 231 nm.