Various Laser Applications

General considerations

Pulsed laser are used in various types of applications:

Material processing: using laser pulses to induce long-term chemical and structural transformations to a target material, as a result of laser-matter interaction (curing, laser marking, etc.), or to remove material from the target, called ablation Ablation(cutting or drilling), resulting in a change of its shape.

Thin layer deposition: using very powerful ultrashort laser pulses to evaporate the surface of a target material, and to deposit it on the surface of another material close by.

Diagnosis: obtaining information about the chemical composition and structure, as well as the temperature and other physical characteristics of a material by analyzing the spectrum of absorption, emission, or scattering from the target material during or/and after matter-laser pulse interaction, or by analyzing ejected material from the target. These diagnosis techniques can be time-integrated or time-resolved (with up to atosecond time resolution).

Imaging: obtaining information about the spatial distribution of features having specific optical properties, composing an heterogeneous material. Linear and/or nonlinear absorption, fluorescence, scattering, interference and diffraction, reflexion, shadow, are processes that can be used to extract spatial information. These imaging techniques ca be time-integrated or time-resolved.

Distance and movement detection: obtaining information bout the distance between a laser-based device and a distant object (range finding), with the possibility to integrate this over the surface of the object to obtain a three dimensional image of it; and obtaining information about the relative speed of the object, or of certain parts of the object, with the possibility to resolve translation and rotation (see LIDAR or laser radar).

Data transmission: this use supposes encoding information in the form of light signals, and transmitting it to long distances. Important processes are linear and nonlinear propagation of light pulses within waveguides, light amplification, and others.

In this article I argue that laser pulses can reproduce very well the effects of ionizing radiation on dielectric materials, including aqueous solutions. Actually one of the most important lessons of this website is that by using laser pulses one can reproduce with great fidelity the effects of any type of ionizing radiation on dielectric materials. Even the dose distribution of heavy charged particles (high LET radiation), presenting the very characteristic peak of Bragg, can be closely reproduced in the F-OB mode. This implies that pulsed lasers can replace ionizing radiation in a number of applications. The advantages in doing so are enormous, to name just a few: reduced time and costs, increased safety and security, diminished complexity of protocols (by eliminating handling dangerous materials, and the need of expensive equipment like synchrotrons or particle accelerators), increased control on effects, miniaturization and automation of experiments, etc. Laser pulses can be used for example as a model to study the effects of ionizing radiation on biological systems.

Material processing

OB mode

OB's destructive power is used for surface processing (ablation) - Figures 1 and 2, and bulk processing (modifying the local physical properties of the material and creating patterns - optical guides, greetings, micro-channels). The OB effect can be very localized, which translates into a very high precision (sub-micron) processing.

The OB's capacity to vaporize the surface of any kind of material has been also found useful in thin layer deposition.

The disruptive OB shock wave was used to demonstrate cell lysis.

B/OB mode

The B/OB mode is less disruptive than the OB mode, and also more selective in terms of which atomic or molecules are ionized, dissociated, or excited. Its spatial confinement is superior to the OB mode, and it can be used in high precision nanoprocessing [1]: surface processing (ablation), and bulk processing (modifying the local physical properties of the material and creating patterns - optical guides, greetings, micro-channels). Undesirable thermal effects can be controlled and even eliminated, reducing collateral damage.

SP mode

The SP mode is used for curing, and in chemistry under radiation.

Applications in medicine

OB mode

B/OB mode

The B/OB mode can be used like the OB mode, offering higher precision, and less collateral damage.

Applications in biology

OB mode

B/OB mode

The B/OB mode is less disruptive than the OB mode, and also more selective in terms of which atomic or molecules are ionized, dissociated, or excited. Its spatial confinement is superior to the OB mode, and it can be used in high precision nanoprocessing [1]. As opposed to the OB mode, the B/OB becomes more appropriate, as the plasma density and the thermal effects can be controlled, and the shock wave can be eliminated, reducing collateral damage. The B/OB mode can than be safely used for microsurgery (burning holes in the cellular membrane, targeted destruction of intracellular structures [2, 3, 4]) -Figure 5, and DNA processing (cutting chromosomes [1]) - Figure 6. This opens the door to very interesting applications, where sub lethal damage can be induced to cells, with the possibility to study the biological role of various intracellular structures.

F mode

To my knowledge there are no studies available for this particular ionization mode. This is an interesting topic for future studies. An interesting project would be to study the indirect effects of filamentary ionization on cells. It had been observed that a high LET (Linear Energy Transfer) ionizing particle that actually misses a cell (passes close to a cell and induces a linear ionization trail in its vicinity) induces apoptosis. This is known as the bystander effect. It is believed that cells possess the ability to detect photolytic species generated by ionizing particles, and are programed to auto-destruction to minimize the risk of becoming mutants, or cancerous. The understanding of the bystander effect, the mechanism by which the cell detects the effects of radiation, as well as the mechanism that triggers apoptosis can lead to new cancer therapies, and new tissue processing techniques. By comparing the filamentary ionization patterns of the F mode, with the ionization tracks of high LET radiation, we can predict that the bystander effect can be induced and studied by using laser pulse.

Another interesting application is the in-vitro study of DNA damage mechanisms, and DNA repair mechanisms, by replacing high LET radiation with laser pulses in the F mode. The filamentary dose distribution, and the uniform ionization density along filaments makes it easy to model the chemistry that follows the passage of the ionizing laser pulse. The same theoretical arsenal developed in radiation science to model radiolysis effects can be directly reapplied in this new context. See the next section for more on this topic.

Applications in radiobiology

These applications are based on the ability of laser pulses to ionize, dissociate, and excite atoms and molecules composing materials, and on our ability to manipulate the dose distribution, and to control the yields of primary and long-term photolytic species generated, and ultimately to control the long-term effects on targets of biological interest. Laser pulses can mimic the effects of any type of ionizing radiation (see my article) on aqueous solutions, and solid dielectric materials. This means that pulsed laser sources can replace radiation sources in some type of applications. Moreover, they can be used to model radiation effects, and to study the effects of radiation on biological systems.

One important application is the study of DNA, protein, membrane damage, and DNA and membrane repair mechanisms: laser pulses are used to induce direct or indirect (free radicals mediated) damages to targets of biological interest, in a controllable fashion. A two or three laser beam scheme can be used to study in time the creation of damages, and the dynamics of repair processes. One laser beam is used as a pump, to induce the damage, and the others, synchronized with the first, are used to monitor the changes with fs to microsecond time resolution.

An interesting effect of laser pulses that follows the ionization processes is the controlled creation of free radicals. This can be used to model and study oxidative stress: laser pulses are used to induce free radicals in a controllable fashion. A two or three laser beam scheme can be used to study in time the effects of these photolytic species on targets of biological interest. One laser beam is used as a pump, to induce the free radical population, and the others, synchronized with the first, are used to monitor the changes with fs to microsecond time resolution.

The characteristic filamentary ionization type of the F mode is very interesting for radiobiology. The geometry is very simple and suitable for modeling, and it offers a comfortable degree of control on the type, and the yield of primary photolytic species. Models already developed in radiation science can be employed to account for long term effects. The F-OB mode can be also used as a model of high LET radiation, with its characteristic Bragg's peak.

An extensive comparison between UV laser radiation and ionizing radiation in terms of water radiolysis/photolysis, and direct and indirect DNA damage was published by D.N. Nicogosyan [16]. Single photon and two-photon processes were considered. Similar studies are needed in the visible and IR, for all ionization modes.

Applications in radiochemistry

These applications are based on the ability of laser pulses to ionize, dissociate and excite atoms and molecules composing materials, and on our ability to manipulate the dose distribution, and to control the long-term effects. The dose distribution, and the relative yield of photolytic species created are controlled by inducing a superposition of ionization modes. The characteristic filamentary ionization type of the F mode is very interesting for radiochemistry. The geometry is very simple and suitable for modeling, and it offers a comfortable degree of control on the type, and the yield of primary photolytic species. Models already developed in radiation science can be employed to account for long term effects.

Optical diagnostic techniques

OB mode

Being very localized, the techniques based on OB have a high spatial resolution, and can be used to study the composition, and structure of very fine grain material aggregates.

Using OB emission as a source of light

These applications are based on considering the OB emission as a broad band non-coherent light source, that can be used for diagnostic techniques involving linear light–matter interactions like one-photon absorption, and non-coherent light scattering [10].

At very high power levels (peta- and exa-Watt), and in the fs time regime, sub-fs coherent X-ray bursts are emitted from the OB region. They can be collected and used for spectroscopic, and imaging purposes. For example A.A. Andreev et al. [35] proposed ways to optimize laser based X-ray sources that can be used for applications in biology.

Analyzing the spectrum of OB emission

These applications are based on considering the OB emissions as a source of information about the chemical composition and structure of the material. The information is encoded in the spectral features of the emission; the time integrated or the time resolved spectral features are analyzed to extract it. This is the base of techniques like: time-resolved laser-induced breakdown spectroscopy (LIBS), and in situ or remote-sensing.

Analyzing matter ejected from a OB zone

This is done by collecting and analyzing (using time-of-flight spectroscopy) the ejected photoelectrons, ions, and other molecular fragments, in the case of surface studies in vacuum. From time integrated spectral features one can deduce the composition and the structure of the material. From time resolved spectral studies one can obtain information on relaxation processes, and on the lifetime of excited states.

Harvesting the acoustic emissions

The acoustic emission from the OB region has also been used in imaging, extracting information about the density distribution within a small body. A similar technique is used by geophysicists, where a dynamite is placed into the ground, and detonated. The sound waves are captured a certain distance away, and analyzed. The difference between their initial and final form contains information on the variations in material density encountered.

B/OB mode

B/OB can also be used to acquire information about the composition and the structure of materials at the molecular level. The information can be extracted by collecting and analyzing the ejected photoelectrons in the case of surface studies in vacuum. The selectivity of MPI processes and the lower plasma density translates into a higher sensitivity then the OB mode. The plasma generated being cooler then in the case of OB, there is no emission that can be used for remote sensing.

F mode

Using the supercontinuum as a coherent broad band light source

In the late 1960's, Alphano and Shapiro [6] discovered the continuum generation phenomena. Later, the strong connection between self-focusing and the continuum generation was firmly established [7-9]. The use of the supercontinuum as a coherent broad-band ultrashort (fs to ns) light source in time-resolved spectroscopy and imaging become very popular.

References

[1] Nanodissection of human chromosomes with near-infrared femtosecond laser pulses; K. König, I. Riemann, W. Fritzsche; Optics Letters, Vol. 26, No. 11, June 1, 2001

[2] Mechanisms of femtosecond laser nanosurgery; of cells and tissues; A. Vogel, J. Noack, G. Huttman, G. Paltauf; Appl. Phys. B 81, 1015–1047 (2005)

[3] Femtosecond laser disruption of subcellular organelles in a living cell; Wataru Watanabe, Naomi Arakawa, Sachihiro Matsunaga, Tsunehito Higashi, Kiichi Fukui, Keisuke Isobe, Kazuyoshi Itoh; Optics Express, Vol. 12, No. 18, 4203; 6 September 2004

[4] Intracellular disruption of mitochondria in a living HeLa cell with a 76-MHz femtosecond laser oscillator; Tomoko Shimada, Wataru Watanabe, Sachihiro Matsunaga, Tsunehito Higashi, Hiroshi Ishii, Kiichi Fukui, Keisuke Isobe, Kazuyoshi Itoh; Optics Express, Vol. 13, No. 24, 9869, 28 November 2005

[5] Mechanisms of femtosecond laser nanosurgery of cells and tissues, A. Vogel, J. Noack, G. Huttman, G. Paltauf; Appl. Phys. B 81, 1015–1047 (2005)

[6] Observation of self-phase modulation and small-scale filaments in crystals and glasses; R. R. Alfano and S. L. Shapiro; Physical Review Letters, Volume 24, Number 11, 16 March 1970

[7] Superbroadening in H₂O and D₂O by self-focused picosecond pulses from a YAIG:Nd laser; W. Lee Smith, P. Liu, and N. Bloembergen; Physical Review A, Volume 15, Number 6, 2396 June 1977

[8] Ultrafast wihte-light continuum generation end self focusing in transparent condensed media; A. Brodeur and S.L. Chin; 1999 Optical Society of America Vol. 16, no. 4/April 1999/J. Opt. Soc. Am. B 637

[9] Band Gap Dependence of the ultrafast white-light continuum; A. Brodeur and S.L. Chin; Phys rev lett, Vol 80, No 20, 4406, 18 may 1998

[10] Time-resolved spectral and spatial description of laser-induced breakdown in air as a pulsed, bright, and broadband ultraviolet–visible light source; Antonio Borghese and Simona S. Merola; Applied Optics, Vol. 37, No. 18, 20 June 1998

[11] Investigation of laser-induced cell lysis using time-resolved imaging; Kaustubh R. Rau, Arnold Guerra III, Alfred Vogel, Vasan Venugopalan; Applied Physics Letters, Vol. 84, No. 15, 12 April 2004

[12] Intratissue surgery with 80 MHz nanojoule femtosecond laser pulses in the near infrared Karsten König, Oliver Krauss and Iris Riemann; Optics Express 171, Vol. 10, No. 3, 11 February 2002

[13] Propagation of ablation channels with multiple femtosecond laser pulses in dielectrics: numerical simulations and experiments; J. R. Vazquez de Aldana, C. Mendez, L. Roso, P. Moreno; J. Phys. D: Appl. Phys. 38 (2005) 2764–2768

[14] A study of the deterministic character of optical damage by femtosecond laser pulses and applications to nanomachining; A.P. Joglekar, H. Liu, G.J. Spooner, E. Meyhofer, G. Mourou, A.J. Hunt, Appl. Phys. B 77, 25–30 (2003)

[15] Prospects of “water-window” X-ray emission from subpicosecond laser plasmas; A.A. Andreev, U. Teubner, I.V. Kurnin, E. Förster; Appl. Phys. B 70, 505–515 (2000)

[16] Two-quantum UV photochemistry of nucleic acids: comparison with conventional low-intensity UV photochemistry and radiation chemistry; D.N. Nicogosyan Int. J. Radiat. Biol., 1990, Vol. 57, No. 2, 233-299