Generation of Arbitrary Frequency Chirps with a Fiber-Based Phase Modulator and Self-Injection-Locked Diode Laser

We present a novel technique for producing pulses of laser light whose frequency is arbitrarily chirped. The output from a diode laser is sent through a fiber-optical delay line containing a fiber-based electro-optical phase modulator. Upon emerging from the fiber, the phase-modulated pulse is used to injection-lock the laser and the process is repeated. Large phase modulations are realized by multiple passes through the loop while the high optical power is maintained by self-injection-locking after each pass. Arbitrary chirps are produced by driving the modulator with an arbitrary waveform generator

From carrier dynamics inside fused silica to control of multiphoton-avalanche ionization for laser machining

Using pump-probe measurements, we characterize carrier decay time inside fused silica and measure deeply bound self-trapped excitons. With pump-probe delay, we also control free carrier injection and the subsequent avalanche process for laser machining applications

Measuring attosecond ionization dynamics inside dielectrics

We resolve attosecond dynamics of multiphoton ionization in solids. We subdivide the laser cycle using differential absorption between the major and the minor axes of elliptically polarized beam. \ua92007 Optical Society of America.Peer reviewed: YesNRC publication: Ye

Cold avalanche ionisation

Peer reviewed: YesNRC publication: Ye

Field dependent avalanche ionization rates in dielectrics

From the pulse length dependence of the absorption of intense ultrashort laser pulses focused inside fused silica, we reveal the role field-assisted collisional ionization plays in the multiphoton ionization process. This constitutes a cold avalanche ionization mechanism that persists at pulse lengths considered too short for a traditional avalanche.Peer reviewed: YesNRC publication: Ye

Demonstration of attosecond ionization dynamics inside transparent solids

Attosecond science has arisen from intense light pulses interacting with low density gases. We show that the initiating process\u2014sub-cycle ionization\u2014also survives in large band gap condensed media. Using fused SiO2 as an example, we measure the differential nonlinear absorption between the major and minor axis of elliptically polarized light. Through simulations that include ionization and light propagation, we confirm that changes in the ellipticity between the incident beam and the transmitted beam encode sub-cycle absorption dynamics. As the pulse duration is increased, we observe that sub-cycle ionization is masked by collisional processes. We propose a general class of methods for measuring attosecond dynamics in condensed media.Peer reviewed: YesNRC publication: Ye

Time and frequency activities at NRC

The National Research Council of Canada (NRC) is currently involved in a number of research projects aimed at improving time and frequency realization based on the accurate and precise stabilization of microwave and optical sources on atomic and molecular transitions. Projects described in this summary will focus on the development of a primary standard for the realization of the SI second based on a cesium atomic fountain and a next generation standard based on an optical transition in a single trapped and laser cooled ion of strontium.The cesium fountain is undergoing evaluations of its systematic shifts for an eventual contribution to TAI and for a re-measurement of the absolute frequency of the strontium ion clock transition at the 10?15 level. The main contribution to the uncertainty budget of the fountain is thought to be caused by the inhomogeneity in the magnitude of the magnetic field in the drift region. The latest measurements of this field are presented. A new strontium ion trap of the endcap design was completed last year. This new system has compensation electrodes and access ports in three orthogonal directions to control the ion position and minimize micromotion. We report preliminary results indicating improved performance of this trap over our previous rf Paul trap. As part of an effort to reduce the systematics shifts to a minimum, the heights of the atomic standards above the geoid were measured with an accuracy of 5 cm, corresponding to a fractional frequency uncertainty of 5 7 10?18 for the gravitational redshift. \ua9 2011 SPIE.Peer reviewed: YesNRC publication: Ye

Orientation-dependent multiphoton ionization in wide band gap crystals

Using different crystalline dielectrics and intense femtosecond laser pulses, we show that nonlinear absorption depends on sample orientation. This arises primarily because of the direction dependence of the effective mass of the electron. The multiphoton nature of the interaction creates a local probe that can be used anywhere in the material. We show that the structure of crystal quartz is not changed by repeated illumination of the focal region with 45 fs pulses. \ua9 2008 The American Physical Society.Peer reviewed: YesNRC publication: Ye

Orientation-dependent multiphoton ionization in wide band gap crystals

Using different crystalline dielectrics and intense femtosecond laser pulses, we show that nonlinear absorption depends on sample orientation. This arises primarily because of the direction dependence of the effective mass of the electron. The multiphoton nature of the interaction creates a local probe that can be used anywhere in the material. We show that the structure of crystal quartz is not changed by repeated illumination of the focal region with 45 fs pulses. \ua9 2008 The American Physical Society.Peer reviewed: YesNRC publication: Ye