Tunable Cw Ti Research Articles

Tunable violet radiation in a quasi-phase-matched periodically poled stoichiometric lithium tantalate waveguide by direct femtosecond laser writing

We report on violet-light generation using the femtosecond-laser written waveguides in periodically poled MgO:LiTaO3 crystal under conditions of third-order quasi-phase matching. Ten parallel depressed cladding waveguides are successfully fabricated with different grating periods in the same sample with fan-out χ(2) grating structures. These waveguides exhibit high optical quality with minimum insertion loss as low as 0.71 dB. Temperature and wavelength tuned second harmonic generation for different waveguides are demonstrated by using a tunable CW Ti sappire laser. Tunable violet second harmonic light has been generated with a single period over the range of 396 nm to 401 nm by varying the crystal temperature from 60 °C to 200 °C. At the quasi-phase matching temperature, 0.37 mW of violet light power at 397.2 nm is generated for a fundamental power of 336.7 mW, corresponding to a normalized conversion efficiency of 0.39%/(W·cm2). Our work contributes to designing tunable and efficient on-chip violet light sources based on femtosecond-laser written waveguides.

Low threshold lasing of bubble-containing glass microspheres by non-whispering gallery mode excitation over a wide wavelength range

Bubble-containing Nd3+-doped tellurite glass microspheres were fabricated by localized laser heating technique to investigate their optical properties for use as microresonators. Fluorescence and excitation spectra measurements were performed by pumping with a tunable CW-Ti:Sapphire laser. The excitation spectra manifested several sharp peaks due to the conventional whispering gallery mode (WGM) when the pumping laser was irradiated to the edge part of the microsphere. However, when the excitation light was irradiated on the bubble position inside the microsphere, “non-WGM excitation” was induced, giving rise to numerous peaks at a broad wavelength range in the excitation spectra. Thus, efficient excitation was achieved over a wide wavelength range. Lasing threshold excited at the bubble position was much lower than that for the excitation at the edges of the microsphere. The lowest value of the laser threshold was 34 μW for a 4 μm sphere containing a 0.5 μm bubble. Efficiency of the excitation at the bubble position with broadband light was calculated to be 5 times higher than that for the edge of the microsphere. The bubble-containing microsphere enables efficient utilization of broadband light excitation from light-emitting diodes and solar light.

Enhancement of stimulated Raman scattering in terrace-microspheres

Terrace-microspheres of high-index glass (BaO-SiO2-TiO2 glass, nD=1.93) containing 0.3 ppm of Nd3+ were used to investigate the interaction between Raman scattering due to a glass matrix and fluorescence due to Nd3+. The terrace-microspheres were pumped with a tunable CW Ti:sapphire laser (790 nm–830 nm wavelength) for changing pumping wavelengths. With pumping in the 800–830 nm wavelength region, there was a spectral overlap between Raman scattering and Nd3+ fluorescence. Under such conditions, Nd3+ fluorescence works as a seeding and an amplifier of stimulated Raman scattering (SRS), resulting in SRS enhancement. With pumping of 20 mW power at around 830 nm wavelength, the terrace-microspheres showed the strongest SRS gain, 5–6 times of that of 790 nm wavelength pumping. SRS thresholds of the terrace-microspheres were improved from 3 mW(790 nm wavelength pumping) to 0.3 mW (830 nm pumping) due to the enhancement effect. The potential application for a multiwavelength Raman laser with a low threshold was demonstrated in the near-IR region (λ=840–940 nm).

Widely tunable, single-mode optical frequency synthesizer with a 100 kHz uncertainty

A tunable cw Ti:sapphire laser is locked to a self-referenced femtosecond frequency comb generated by an erbium-doped fiber laser thereby creating a single-frequency optical frequency synthesizer. This synthesizer has a tuning range of 760-820 nm with an absolute frequency uncertainty less than 100 kHz. We demonstrate the precision of this cw optical frequency synthesizer by measuring the optical frequency of several transitions on the D2 lines of 85Rb and 87Rb using a saturated absorption spectrometer.

Z-형태의 대칭형 레이저 공진기 구조를 갖는 연속 발진 및 Kerr-렌즈 모드-록킹되는 티타늄 사파이어 레이저의 설계와 동작 특성

티타늄 사파이어 레이저에 대한 활용도를 높기 위하여 4개의 거울로 구성된 Z-형태의 대칭형 레이저 공진기를 구성하여 넓은 파장가변성을 갖는 고효율 연속 발진 티타늄 사파이어 레이저를 제작하였다. 또한 Kerr-렌즈 모드-록킹(KLM)을 일으키기 위한 KLM 강도 및 공진기 모드 크기가 Kerr 매질을 포함하는 Z-형태의 대칭형 공진기에 대하여 공진기 내의 위치, 내부 공진기 레이저 출력 및 안정 파라메터 등에 의존함을 확인하였고, 이를 근거로 하여 펌핑 효율이 높고 KLM 강도가 강한 KLM 티타늄 사파이어 레이저를 제작하여 출력 특성, 펄스폭 및 스펙트럼 반치폭 등을 측정하였다. 그 결과 연속 발진 티타늄 사파이어 레이저의 출력에 대한 기울기 효율은 31.3%이고, 5W의 Ar-이온 펌핑 레이저 출력에 대해 최대 1420㎽의 평균 출력을 얻을 수 있었으며, 파장가변 영역은 730㎚~908㎚까지 모두 700㎽ 이상의 평균 출력을 보였다. 자체-조리개 효과에 의한 KLM 동작 또한 쉽게 얻을 수 있었으며, KLM된 티타늄 사파이어 레이저로부터 출력에 대한 기울기 효율은 16%이고, 5W 펌핑 출력에 대해 최대 500㎽의 평균 출력을 얻었다. 또한 중심 파장 807㎚에서 스펙트럼 반치폭이 33㎚이며, 펄스 반복률이 82㎒인 27fs의 안정된 짧은 펄스를 얻을 수 있었다. We have constructed a high efficiency and broad tunable cw Ti:sapphire laser with a four-mirror symmetric Z-type laser cavity to increase the laser usability. From theoretical analyses and experimental data for a symmetric Z-type laser cavity containing a Kerr medium, the cavity mode size and the Kerr-lens mode-locking (KLM) strength for KLM lasers can be confirmed as function of the position in the cavity, the intracavity laser power, and the stability parameter. As a result, the slope efficiency and the maximum average output power of cw Ti:sapphire laser at 5 W pumping power of Ar-ion laser were 31.3% and 1420 ㎽ respectively. The tunablility was ranged from 730 ㎚ to 908 ㎚ with average output power above 700 ㎽. We obtained the KLM operation easily by self-aperturing effect in the Kerr medium and the slope efficiency and the maximum average output power of KLM Ti:sapphire laser was 16% and 550 ㎽ respectively. The spectral bandwidth was 33 ㎚ at the center wavelength of 807 ㎚ and the pulse width was 27 fs with a repetition rate of 82 ㎒.

Efficient pumping scheme for neodymium-doped materials by direct excitation of the upper lasing level

An efficient pumping scheme that involves direct excitation of the upper lasing level of the Nd(3+) ion is demonstrated experimentally. The results obtained for direct upper laser level pumping of Nd:YAG R2 (869 nm) and Nd:YVO(4) (880 nm) were compared with traditional approximately 808-nm pump band excitation. A tunable cw Ti:sapphire laser was used as the pump source. In Nd:YAG, the oscillator slope efficiency increased by 10% and the threshold decreased by 11%. In Nd:YVO(4), the slope efficiency increased by 5% and the threshold decreased by 11%. These results agree with theory. The increase in optical efficiency indicates that laser material thermal loading can be substantially reduced.

Experimental Study of the NaK 31Π State

We report the results of an optical–optical double resonance experiment to determine the NaK 31Π state potential energy curve. In the first step, a narrow band cw dye laser (PUMP) is tuned to line center of a particular 2(A)1Σ+(v′,J′) ← 1(X)1Σ+(v",J") transition, and its frequency is then fixed. A second narrowband tunable cw Ti:Sapphirelaser (PROBE) is then scanned, while 31Π → 1(X)1Σ+violet fluorescence is monitored. The Doppler-free signals accurately map the 31Π(v,J) ro-vibrational energy levels. These energy levels are then fit to a Dunham expansion to provide a set of molecular constants. The Dunham constants, in turn, are used to construct an RKR potential curve. Resolved 31Π(v,J) → 1(X)1Σ+(v",J") fluorescence scans are also recorded with both PUMP and PROBE laser frequencies fixed. Comparison between observed and calculated Franck–Condon factors is used to determine the absolute vibrational numbering of the 31Π state levels and to determine the variation of the 31Π → 1(X)1Σ+transitiondipole moment with internuclear separation. The recent theoretical calculation of the NaK 31Π state potential reported by Magnier and Millié (1996,Phys. Rev. A54, 204) is in excellent agreement with the present experimental RKR curve.

Cell damage in near-infrared multimode optical traps as a result of multiphoton absorption

We report on cell damage of single cells confined in continuous-wave (cw), near-infrared (NIR) multimode optical traps as a result of multiphoton absorption phenomena. Trapping beams at NIR wavelengths less than 800 nm are capable of damaging cells through a two-photon absorption process. Cell damage is more pronounced in multimode cw traps compared with single-frequency true cw NIR traps because of transient power enhancement by longitudinal mode beating. Partial mode locking in tunable cw Ti:sapphire lasers used as trapping beam sources can produce unstable subnanosecond pulses at certain wavelengths that amplify multiphoton absorption effects significantly. We recommend the use of single-frequency long-wavelength NIR trapping beams for optical micromanipulation of vital cells.

Vibrationally resolved resonant two-photon ionization spectroscopy of the 1 3Σ +g(b)→1 3Σ +u(X) transition of Na 2

Na 2 molecules in the weakly bound lowest triplet state 1 3Σ u + are formed in a cold supersonic argon beam seeded with sodium. They are excited by a tunable cw Ti:sapphire laser into levels of the 1 3Σ g + state which are ionized by an argon ion laser. From a vibrational analysis of the resonant two-photon ionization (RTPI) spectrum the constants T e=17972±4 cm −1, ω e=100.5±0.9 cm −1 and ω eχ e=0.57±0.03 cm −1 are obtained for the Na (1 3Σ g +) state.