Jianping Cao

External cavity diode laser with kilohertz linewidth by a monolithic folded Fabry–Perot cavity optical feedback

We present a extended-cavity diode laser (ECDL) with kilohertz linewidth by optical feedback from a monolithic folded Fabry-Perot cavity (MFC). In our experiments, an MFC replaces the retroreflecting mirror in the traditional ECDL configuration. Beat-note measurements between this MFC-ECDL and a narrow-linewidth reference laser are performed and demonstrate that the linewidth of this MFC-ECDL is about 6.8 kHz. Phase locking of this MFC-ECDL to the reference laser is achieved with a unity gain as small as 10.2 kHz.

100-Hz Linewidth Diode Laser With External Optical Feedback

We present a narrow-linewidth diode laser with optical feedback from a high-finesse two-mirror nonconfocal cavity. The lasers full-width-at-half-maximum linewidth is reduced to 100 Hz, and its instantaneous linewidth to 30 Hz in the Lorentzian fitting. To the best of our knowledge, it is the narrowest linewidth ever achieved with the optical feedback method. The laser phase noise has been significantly reduced by more than 50 dB in the frequency range from 10 Hz to 10 kHz. Our experiment demonstrates the efficient laser linewidth reduction and phase noise suppression by the optical feedback technique.

High-finesse cavity external optical feedback DFB laser with hertz relative linewidth

We report hertz level relative linewidth distributed feedback diode lasers with external optical feedback from a high finesse F-P cavity, and demonstrate the efficient phase noise suppression and laser linewidth reduction of the optical feedback technique. The laser phase noise is dramatically suppressed throughout the measurement frequency range. Especially at the Fourier frequency of 17 kHz, approximately the linewidth of the F-P reference cavity, the laser phase noise is significantly suppressed by more than 92 dB. Above this Fourier frequency, the noise maintains a white phase noise plateau as low as -124.4 dBc/Hz. The lasers FWHM linewidth is reduced from 7 MHz to 4.4 Hz, and its instantaneous linewidth is 220 mHz in the Lorentzian fitting.

Quasi synchronous tuning for grating feedback lasers

A general analytical form of the round trip phase shift in grating feedback diode lasers is proposed. Using the new form, it is obvious that the round trip phase shift can be independent of rotation angle in first order approximation when only one restriction condition is met. We call this the quasi synchronous tuning (QST) condition. In the QST region, a considerably large mode hopping free tuning range can be obtained. An adjustment structure with only one freedom is needed to accurately find and locate the quasi synchronous pivot, which is not strictly confined on the grating surface and its extension. It means that the external cavity diode lasers design can be easier and the laser can be more stable and reliable.

Hyperfine structure of molecular-iodine absorption spectroscopy at 561nm

An 1123-nm single-frequency laser with 1-W output power has been made by home, and 10-mW output power double frequency at 561nm is obtained. The modulation transform spectroscopy is used to scan the hyperfine structure lines of molecular iodine absorption spectroscopy transitions at 561nm. Four transition spectroscopy bands of ¹²⁷I<inf>2</inf> are observed, and transitions of P(58)22−1 and R(62)22−1 are discussed to be references of 561-nm ¹²⁷I<inf>2</inf> optical frequency standard.

More than 200 mW blue light source from an integrative ring cavity

An integrative external-enhancement ring cavity has been designed to acquire 461 nm blue light source with high output power. Using a 30-mm-long quasi-phase-matched periodically-poled KTP doubling crystal, we have obtained total more than 210 mW blue light from 287 mW coupling incident power with the net conversion efficiency over 70%.

Modulation Transfer Spectroscopy of

Hyperfine structures of ¹²⁷<i>I</i>₂ absorption transitions near 561 nm are observed via modulation transfer spectroscopy by a homemade Nd:YAG monolithic nonplanar ring laser with its second harmonic generation (SHG) using a single-pass PPMgO:LN crystal. The observed <i>I</i>₂ transitions are assigned according to theoretical calculation results of the <i>I</i>₂ B-X transition. Two Nd:YAG lasers are locked to the 15th component of the ¹²⁷<i>I</i>₂ P(58)22-1 transition, and the measured frequency stability of these lasers is 1 × 10^-13 for a 1-s averaging time. Frequency shifts with changing iodine cell vapor pressure and pump power are measured by observing the heterodyne beat between two <i>I</i>₂-stabilized lasers.

{}^{127}I_{2}

Atmospheric pressure sensitivity of the ultrastable monolithic nonplanar ring laser has been observed in optic frequency standard experiments. Atmospheric pressure perturbations affect the frequency stability of monolithic nonplanar ring lasers about 3.7 GHz/kPa. In this paper, this susceptibility is measured and quantitatively analyzed. This phenomenon needs to be cancelled in portable device of the 532-nm I2-stabilized optical frequency standards.