Noboru Uehara

Accurate measurement of ultralow loss in a high-finesse Fabry-Perot interferometer using the frequency response functions

We describe the accurate measurement of ultralow loss in a high-finesse Fabry-Perot interferometer using a diode-pumped Nd:YAG laser locked to the longitudinal mode with an active frequency-stabilization technique. By measuring the resonance full width and the free spectral range with the frequency response functions, and by measuring the transmission efficiency on resonance, the finesse and the loss at 1064 nm are accurately measured to be 78100 ± 1200 (reflectance of 99.99598 ± 0.00006%) and 1 5.9 ±2.0 × 10−6 (15.9 ± 2.0 ppm), respectively.

Ultralow-loss mirror of the parts-in-10 6 level at 1064 nm

We describe an ultralow-loss and high-reflectance mirror at 1064 nm. A Fabry-Perot cavity is fabricated with two mirrors to measure the finesse and the transmission efficiency on resonance. The finesse was cross checked by two different methods: measurements of the cavity decay time and of the frequency-response function. As a result, a loss of 6 +/- 6 x 10(-6) (6 +/- 6 parts in 10(6), scatter and absorption) and a finesse of 2236 +/- 54 were measured during the cavity decay time. This result coincides with that of the response function within accuracies cited above. To our knowledge, the loss is the lowest obtained at 1064 nm.

193-mHz beat linewidth of frequency-stabilized laser-diode-pumped Nd:YAG ring lasers

We describe frequency-stabilized laser-diode-pumped Nd:YAG ring lasers locked to a high-transmission and high-finesse reference Fabry-Perot cavity. The cavity has a resonant linewidth of 38.0 kHz, a finesse of 19,400, and a transmission efficiency of 79.4% for the TEM(00) mode. We measure the frequency stability by locking two lasers one free spectral range apart and observe the heterodyne beat signal. As a result, the spectral densities of frequency noise are reduced to 10 mHz/ radicalHz, and a beat linewidth of 193 mHz is obtained. The linewidth is 0.73 times the Schawlow-Townes limit.

Continuous-wave TEM00-mode 26.5-W-output virtual-point-source diode-array-pumped Nd:YAG laser.

We describe a novel side-pumping configuration of the virtual-point-source diode-array-pumped Nd:YAG laser with 32 cw 10-W laser diodes. A new concept of the virtual point source and an image-relay system are proposed for the generation of a Gaussian-like pumping profile with an optically thin gain medium. A cw linearly polarized TEM00-mode, 26.5-W output was obtained at a diode pump power of 171 W. The M2 values at the x and y axes were measured to be Mx2=1.03 and My2=1.20, respectively.

Spectroscopic Measurements of a High-Concentration Yb 3+:LiYF 4 Crystal

We describe the spectroscopic measurements of Yb3+:LiYF4 crystal at room temperature. The absorption and the emission spectra are measured with a 40.5 at% Yb3+ doped crystal. A maximum absorption coefficient of 42 cm-1 for the π polarization is measured at 960 nm with a spectral fullwidth of 12 nm. The upper-state (2F5/2) lifetime is measured to be 2.0 ms. The emission cross section at an oscillation wavelength of 1018 nm for the π and the σ polarizations are measured to be 5.3 ×10-21 cm2 and 4.7×10-21 cm2, respectively. The ground-state absorption coefficient at 1018 nm for the π and the σ polarizations are measured to be 4.0 cm-1 and 1.6 cm-1, respectively.

Ultrahigh-frequency stabilization of a diode-pumped Nd:YAG laser with a high-power-acceptance photodetector

We describe the ultrahigh-frequency stabilization of a diode-pumped Nd:YAG laser by use of a high-poweracceptance photodetector. The photodetector, which is constructed with an optical power divider and eight combined photodiodes, is developed to reduce shot-noise-limited FM noise. The laser frequency is locked to a Fabry-Perot cavity with a finesse of 25,600 by the Drever-Hall technique. By using the optical power of 47 mW at the photodetector, we reduce the relative FM noise at the error signal to the shot-noise limit of 4.2x10(-5) Hz/ radicalHz below the Fourier frequency of 500 Hz.

Frequency Stabilization of Two Diode-Pumped Nd:YAG Lasers Locked to Two Fabry-Perot Cavities

We describe frequency stabilization of two laser-diode-pumped Nd:YAG lasers independently locked to two high-finesse Fabry-Perot cavities. The frequency noise (FM noise) is reduced to the shot noise limit of 0.37 mHz/√Hz at the error signal. A heterodyne beat note between two locked lasers is used to measure the frequency stability, and the beat linewidth of 16 Hz and the root Allan variance of 19 Hz at time interval of 3 ms are measured. We also measured an effect of angular ground vibration to FM noise. The sensitivity of 3.38 mHz/√Hz / nrad below 10 nradrms is obtained in our system.

Laser-diode-pumped solid state lasers for gravitational wave antenna

The development of frequency stabilized lasers related to the gravitational wave detection is reported. The beat linewidth of laser diode pumped YAG lasers stabilized to the same cavity was measured to be 193 mHz. The source of frequency fluctuation was analyzed carefully. For the higher sensitivity for gravitational wave detection new designs, 100 micrometers thick YVO4 active mirror and virtual source clad pumping YAG lasers are discussed from the view of scaling physics.

920 kHz, low-repetition rate, mode-locked Er-doped fiber ring laser at 1534 nm

We describe a 920 kHz, low-repetition rate, mode-locked Er-doped fiber ring laser. Transform-limited pulse duration of 813 fs, assuming a Gaussian pulse shape is obtained with output pulse energy of 4.3 nJ at 1534 nm. This is the lowest repetition rate in the fundamental mode ever reported to our knowledge.

Short-tenn spectrl stabilit of super-continuum source using noise-like pulses generated from an EDF laser

We experimentally investigate shot-term spectral stability of supercontinuum sources. We show that a supercontinuum source using noise-like pulses generated from an EDF fiber laser achieves excellent stability within plusmn0.05dB in the almost entire wavelength range