Mamoru Endo

Kerr-lens mode-locked Yb:KYW laser at 4.6-GHz repetition rate

We developed a laser-diode pumped, 3.32-GHz repetition-rate, Yb:KYW Kerr-lens mode-locked laser with a bowtie cavity. The spectrum width is 10 nm around 1050 nm with the output power of 13.5 mW.

Direct 15-GHz mode-spacing optical frequency comb with a Kerr-lens mode-locked Yb:Y 2 O 3 ceramic laser

A 15-GHz mode spacing optical frequency comb based on a Kerr-lens mode-locked Yb:Y2O3 ceramic laser has been developed. Individual modes were clearly resolved by a commercial spectrometer. To demonstrate the long-term operation of the optical frequency comb, a single longitudinal mode was phase-locked to a frequency-stabilized continuous wave laser and the repetition rate to a radio frequency standard. To the best of our knowledge, 15 GHz is the largest reported mode spacing (repetition rate) for both a Kerr-lens mode-locked laser and a direct femtosecond laser based-optical frequency comb.

Development of compact and ultra-high-resolution spectrograph with multi-GHz optical frequency comb

In recent years, a calibration method for an astronomical spectrograph using an optical frequency comb (OFC) with a repetition rate of more than ten GHz has been developed successfully [1-5]. But controlling filtering cavities that are used for thinning out longitudinal modes precludes long term stability. The super-mode noise coming from the fundamental repetition rate is an additional problem. We developed a laser-diode pumped Yb:Y2O3 ceramic oscillator, which enabled the generation of 4-GHz (maximum repetition rate of 6.7 GHz) pulse trains directly with a spectrum width of 7 nm (full-width half-maximum, FWHM), and controlled its optical frequency within a MHz level of accuracy using a beat note between the 4-GHz laser and a 246-MHz Yb-fiber OFC. The optical frequency of the Yb-fiber OFC was phase locked to a Rb clock frequency standard. Furthermore we also built a table-top multi-pass spectrograph with a maximum frequency resolution of 600 MHz and a bandwidth of 1 nm using a large-size high-efficiency transmission grating. The resolution could be changed by selecting the number of passes through the grating. This spectrograph could resolve each longitudinal mode of our 4-GHz OFC clearly, and more than 10% throughput was obtained when the resolution was set to 600 MHz. We believe that small and middle scale astronomical observatories could easily implement such an OFC-calibrated spectrograph.

Unconditional conversion between a single-photon state and a coherent-state superposition via squeezing operation

We experimentally demonstrate a conversion of a single-photon state into a superposition of two weak coherent states and its inverse, via squeezing operation based on offline-prepared squeezed states, measurement and feedforward.

Multi-GHz mode-locked lasers and comb-resolved spectroscopy

A femtosecond optical frequency comb with a maximum repetition frequency of 15 GHz was developed and successfully applied to comb-resolved spectroscopy, as well as the manipulation of acoustic phonons in a silica fiber.

Kerr-lens mode-locked Yb:KYW laser at 3.3-GHz repetition rate

We developed a laser-diode pumped, 3.32-GHz repetition-rate, Yb:KYW Kerr-lens mode-locked laser with a bowtie cavity. The spectrum width is 10 nm around 1050 nm with the output power of 13.5 mW.