We report on an all-solid-state rapidly tunable pulsed coherent 6-10 μm light source achieved in an optical parametric oscillator (OPO) pumped with an electronically tuned Cr:ZnSe laser and its application to lidar remote sensing for environmental detection. We designed a lidar system using the 6-10 μm light source and a telescope with a primary mirror of 50 cm and a high-efficient HgCdTe detector. The lidar system would be a valuable system in the measurement of chemical agents in the 100-300 m.
We are developing a laser guide star (LGS) system for the
188-elements Adaptive Optics system (AO188) of the
Subaru telescope. In this paper we describe the results of the performance tests of the LGS system. The beam
that excites sodium atoms at 90 km altitude of the LGS is generated by the following sequence. The source
of the beam is a quasi-CW mode locked sum-frequency generating 589 nm laser. This laser beam propagates
through a diagnostics system for measuring the wavelength and the beam quality. Then it couples into a solidcore
photonic crystal fiber cable for transmitting the beam to a telescope for launching the beam (LLT: Laser
Launching Telescope). The output beam from this fiber cable is collimated by the optics mounted on the
LLT. This collimated beam is expanded by the LLT and launched into the sky. We executed several engineering
observations of the LGS system from 2009 for confirming the performance of all the components in this sequence.
We also report the quality of the LGS.
Integrated computational model for operation of co-doped Tm,Ho solid-state lasers is developed coupling (i) 8-level rate equations with (ii) TEM00 laser beam distribution, and (iii) complex heat dissipation model. Simulations done for Q-switched ≈0.1 J giant pulse generation by Tm,Ho:YLF laser show that ≈43 % of the 780 nm light diode side-pumped energy is directly transformed into the heat inside the crystal, whereas ≈45 % is the spontaneously emitted radiation from <sup>3</sup>F<sub>4</sub>, <sup>5</sup>I<sub>7</sub> , <sup>3</sup>H<sub>4</sub> and <sup>3</sup>H<sub>5</sub> levels. In water-cooled operation this radiation is absorbed inside the thermal boundary layer where the heat transfer is dominated by heat conduction. In high-power operation the resulting temperature increase is shown to lead to (i) significant decrease in giant pulse energy and (ii) thermal lensing.
This paper reports the experimental results on the phase-matching properties of AgGaGeS<sub>4</sub> for second-harmonic
generation (SHG) at 0.8 &mgr;m that was achieved by using the KTP optical parametric oscillator and difference-frequency
generation (DFG) at 2 and 5-12 &mgr;m that were achieved by using the dual-wavelength emitting Ti:Sapphire laser and the
Nd:YAG laser. Two AgGaGeS<sub>4</sub> samples showed locally different phase-matching conditions which were probably
caused by the various crystal compositions. The new Sellmeier equations were constructed using the literature value of
the refractive indices and compared with the experimental data. A satisfactory agreement between the model calculation
and the experiments is obtained.
We report an all-solid-state coherent 589 nm light source in single-pass sum-frequency generation (SFG) with actively
mode-locked Nd:YAG lasers for the realization of sodium lidar and laser guide star adaptive optics. The Nd:YAG
lasers are constructed as a LD-side-pumped configuration and are operated at 1064 and 1319 nm for 589 nm light
generation in SFG. Output powers of 16.5 and 5.3 W at 1064 and 1319 nm are obtained with two pumping chambers.
Each chamber consisted of three 80-W-LD arrays. Single transverse mode TEM<sub>00</sub>; M<sup>2</sup> ~1.1 is achieved with adjustment
of cavity length considering thermal lens effect with increase of input LD power. The cavity length is set to
approximately 1 m. Accordingly the mode-locked lasers are operated at a repetition rate of approximately 150 MHz.
Synchronization of two pulse trains at 1064 and 1319 nm is accomplished by control of phase difference between two
radio frequencies input in acousto-optic mode-lockers. Then temporal delay is controlled with a resolution of 37
ps/degree. Pump beams are mixed in periodically poled stoichiometric lithium tantalate (PPSLT) without an
antireflection coating. The effective aperture and length of the crystal are 0.5 × 2 mm<sup>2</sup> and 15 mm. When input intensity
is set at 5.6 MW/cm , an average output power of 4.6 W is obtained at 589.159 nm. Precise tuning to the sodium D<sub>2</sub>
line is accomplished by thermal control of etalons set in the Nd:YAG lasers. The output power at 589.159 nm is stably maintained within ±1.2% for 8 hours.
The purpose of this paper is to report on the current status of developing the new laser guide star (LGS) facility for the Subaru LGS adaptive optics (AO) system. Since two major R&D items, the 4W-class sum-frequency generating laser<sup>1</sup> and the large-area-core photonic crystal fiber<sup>2</sup>, have been successfully cleared, we are almost ready to install the LGS facility to the Subaru Telescope. Also we report the result for LGS generation in Japan.
We developed a high power and high beam quality 589 nm coherent light source by sum-frequency generation in order to utilize it as a laser guide star at the Subaru telescope. The sum-frequency generation is a nonlinear frequency conversion in which two mode-locked Nd:YAG lasers oscillating at 1064 and 1319 nm mix in a nonlinear crystal to generate a wave at the sum frequency. We achieved the qualities required for the laser guide star. The power of laser is reached to 4.5 W mixing 15.65 W at 1064 nm and 4.99 W at 1319 nm when the wavelength is adjusted to 589.159 nm. The wavelength is controllable in accuracy of 0.1 pm from 589.060 and 589.170 nm. The stability of the power holds within 1.3% during seven hours operation. The transverse mode of the beam is the TEM<sub>00</sub> and M<sup>2</sup> of the beam is smaller than 1.2. We achieved these qualities by the following technical sources; (1) simple construction of the oscillator for high beam quality, (2) synchronization of mode-locked pulses at 1064 and 1319 nm by the control of phase difference between two radio frequencies fed to acousto-optic mode lockers, (3) precise tunability of wavelength and spectral band width, and (4) proper selection of nonlinear optical crystal. We report in this paper how we built up each technical source and how we combined those.
We are developing Laser Guide Star Adaptive Optics (LGSAO) system for Subaru Telescope at Hawaii, Mauna Kea. We achieved an all-solid-state 589.159 nm laser in sum-frequency generation. Output power at 589.159 nm reached 4W in quasi-continuous-wave operation. To relay the laser beam from laser location to laser launching telescope, we used an optical fiber because the optical fiber relay is more flexible and easier than mirror train. However, nonlinear scattering effect, especially stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS), will happen when the inputted laser power increases, i.e., intensity at the fiber core exceed each threshold. In order to raise the threshold levels of each nonlinear scattering, we adopt photonic crystal fiber (PCF). Because the PCF can be made larger core than usual step index fiber (SIF), one can reduce the intensity in the core. We inputted the high power laser into the PCF whose mode field diameter (MFD) is 14 μm and the SIF whose MFD is 5 μm, and measured the transmission characteristics of them. In the case of the SIF, the SRS was happen when we inputted 2 W. On the other hand, the SRS and the SBS were not induced in the PCF even for an input power of 4 W. We also investigated polarization of the laser beam transmitting through the PCF. Because of the fact that the backscattering efficiency of exciting the sodium layer with a narrowband laser is dependent on the polarization state of the incident beam, we tried to control the polarization of the laser beam transmitted the PCF. We constructed the system which can control the polarization of input laser and measure the output polarization. The PCF showed to be able to assume as a double refraction optical device, and we found that the output polarization is controllable by injecting beam with appropriate polarization through the PCF. However, the Laser Guide Star made by the beam passed through the PCF had same brightness as the state of the polarization.
We present the development status of the laser system for Subaru Laser Guide Star Adaptive Optics System. We are manufacturing the quasi-continuous-wave sum frequency laser as a prototype. The optical efficiency of sum frequency generation normalized by the mode-locked fundamental YAG (1064 nm) laser output power is achieved to be 14 % using the non-linear crystal, periodically poled potassium titanyl phosphate (PPKTP). Output power at sodium D2 line was about 260 mW. The optical relay fiber and the laser launching telescope are also described in this paper. For the optical relay fiber, we are testing an index guided photonic crystal fiber (PCF), whose core material is filled by fused silica, and whose clad has close-packed air holes in two dimension. The coupling efficiency was evaluated as about 80 % using 1mW He-Ne laser. We introduce the design of laser launching telescope (LLT), which is a copy of VLT laser launching telescope, and the interface to the Subaru Telescope.
A variety of progress concerned with an electronically tuned Ti:sapphire laser with an acousto-optic tunable filter for the purpose of spectroscopic applications are described. The major advances are that fast and random access tuning can be achieved in a tuning range of 690-1056 nm by computer control without any mechanical changes of cavity. The access speed reached to 250 microsecond(s) . The Ti:sapphire laser also provided tunable dual-wavelength operation in a single laser cavity with introducing two different radio frequencies at same time. The operation was promising as a pumping source of difference-frequency generation. Difference-frequency generation of non-mechanical tuning was realized from 6.0 to 7.1 micrometers , from 6.8 to 8.6 micrometers , and from 8.5 to 11.3 micrometers for the phase-matching angle at 58, 53, and 46 deg, respectively, using the dual-wavelength laser. Furthermore, the electronic tuning by acousto-optic tunable filter achieved broad tunable picosecond pulse generation with only computer control.